| 1. |
- Bower, K. N., et al.
(author)
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ACE-2 HILLCLOUD. An overview of the ACE-2 ground-based cloud experiment
- 2000
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 52:2, s. 750-778
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Journal article (peer-reviewed)abstract
- The ACE-2 HILLCLOUD experiment was carried out on the island of Tenerife in June-July 1997 to investigate the interaction of the boundary layer aerosol with a hill cap cloud forming over a ridge to the north-east of the island. The cloud was used as a natural flow through reactor to investigate the dependence of the cloud microphysics and chemistry on the characteristics of the aerosols and trace gases entering cloud, and to simultaneously study the influence of the physical and chemical processes occurring within the cloud on the size distribution, chemical and hygroscopic properties of the aerosol exiting cloud. 5 major ground base sites were used, measuring trace gases and aerosols upwind and downwind of the cloud, and cloud microphysics and chemistry and interstitial aerosol and gases within the cloud on the hill. 8 intensive measurement periods or runs were undertaken during cloud events, (nocturnally for seven of the eight runs) and were carried out in a wide range of airmass conditions from clean maritime to polluted continental. Polluted air was characterised by higher than average concentrations of ozone (> 50 ppbv), fine and accumulation mode aerosols (> 3000 and > 1500 cm -3 , respectively) and higher aerosol mass loadings. Cloud droplet number concentrations N, increased from 50 cm -3 in background maritime air to > 2500 cm -3 in aged polluted continental air, a concentration much higher than had previously been detected. Surprisingly, N was seen to vary almost linearly with aerosol number across this range. The droplet aerosol analyser (DAA) measured higher droplet numbers than the corrected forward scattering spectrometer probe (FSSP) in the most polluted air, but at other times there was good agreement (FSSP = 0.95 DAA with an r 2 = 0.89 for N < 1200 cm -3 ). Background ammonia gas concentrations were around 0.3 ppbv even in air originating over the ocean, another unexpected but important result for the region. NO 2 was present in background concentrations of typically 15 pptv to 100 pptv and NO 3 . (the nitrate radical) was observed at night throughout. Calculations suggest NO 3 . losses were mainly by reaction with DMS to produce nitric acid. Low concentrations of SO 2 (~30 pptv), HNO 3 and HCl were always present. HNO 3 concentrations were higher in polluted episodes and calculations implied that these exceeded those which could be accounted for by NO 2 oxidation. It is presumed that nitric and hydrochloric acids were present as a result of outgassing from aerosol, the HNO 3 from nitrate rich aerosol transported into the region from upwind of Tenerife, and HCl from sea salt aerosol newly formed at the sea surface. The oxidants hydrogen peroxide and ozone were abundant (i.e., were well in excess over SO 2 throughout the experiment). Occasions of significant aerosol growth following cloud processing were observed, particularly in cleaner cases. Observations and modelling suggested this was due mainly to the take up of nitric acid, hydrochloric acid and ammonia by the smallest activated aerosol particles. On a few occasions a small contribution was made by the in-cloud oxidation of S(IV). The implications of these results from HILLCLOUD for the climatologically more important stratocumulus Marine Boundary Layer (MBL) clouds are considered.
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| 2. |
- Flynn, Michael J., et al.
(author)
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Modelling cloud processing of aerosol during the ACE-2 HILLCLOUD experiment
- 2000
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 52:2, s. 779-800
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Journal article (peer-reviewed)abstract
- A numerical model has been used to simulate the conditions observed during the ACE-2 Hillcloud experiment and to study the processes which may be taking place. The model incorporates gas phase chemistry of sulphur and nitrogen compounds upstream of the cloud, and the interaction of aerosol, precursor trace gases and oxidants within the cloud. Gas phase and aerosol inputs to the model have been provided from measurements made in the field. Dynamics of the air flow over the hill consisted of simple prescribed dynamics based on wind speed measurements, and also for some cases modelled dynamics. In this modelling study, it was found that during clean case studies particles down to 40-55 nm diameter were activated to form cloud droplets, the total number of droplets formed ranging from 200 to 400 drops/cm3. Significant modification of the aerosol spectra due to cloud processing was observed. In polluted cases particles down to 65-80 nm diameter were activated to form cloud droplets, the total number of droplets ranging from 800 to 2800 drops/cm3. Modification of the aerosol spectra due to cloud processing was slight. In all cases, changes in the aerosol spectra were due to both the uptake of HNO3, HCl, NH3 and SO2 from the gas phase, (the SO2 being oxidised to sulphate) and the repartitioning of species such as HNO3, HCl, and NH3 from larger particles onto smaller ones. Modelling results have been compared with observations made. Modelled droplet numbers are typically within 20% of the best measured values. The mode of the droplet distribution typically around 10-20 μm for clean cases and 4-8 μm for polluted cases was found to be in good agreement with the measured values of 10-25 μm for clean cases, but not in such good agreement for polluted cases. Measurements of upwind and interstitial aerosol distributions showed that the smallest particles activated were 30 and 50 nm for clean and polluted cases respectively, slightly smaller than the model values quoted above. Measured upwind and downwind aerosol spectra showed similar modification to that predicted by the model in eight out of the eleven model runs carried out. Chemistry measurements also give general evidence for both the uptake of species from the gas phase, and repartitioning of species from large particles onto smaller ones, though comparisons for individual cases are more difficult. From this modelling study, it can be concluded that in general, in the remote environment the exchange of hydrochloric acid, nitric acid and ammonia between aerosol particles and take up from the gas phase in the vicinity of cloud may be a very important mechanism in regulating the evolution of the aerosol spectrum. Further, the much more linear relationship between cloud droplet and accumulation mode aerosol number, which was observed in the measurements made during the ACE-2 HILLCLOUD project is supported by these modelling results. The implications of this for the indirect effect will be explored in future work.
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| 3. |
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| 4. |
- Bäckstrand, Kristina, et al.
(author)
-
Non-methane volatile organic compound flux from a subarctic mire in Northern Sweden
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:2, s. 226-237
-
Journal article (peer-reviewed)abstract
- Biogenic NMVOCs are mainly formed by plants and microorganisms. They have strong impact on the local atmospheric chemistry when emitted to the atmosphere. The objective of this study was to determine if there are significant emissions of non-methane volatile organic compounds (NMVOCs) from a subarctic mire in northern Sweden. Subarctic peatlands in discontinuous permafrost regions are undergoing substantial environmental changes due to their high sensitivity to climate warming and there is need for including NMVOCs in the overall carbon budget. Automatic and manual chamber measurements were used to estimate NMVOC fluxes from three dominating subhabitats on the mire during three growing seasons. Emission rates varied and were related to plant species distribution and seasonal net ecosystem exchange of carbon dioxide. The highest fluxes were observed from wetter sites dominated by Eriophorum and Sphagnum spp. Total NMVOC emissions from the mire (similar to 17 ha) is estimated to consist of similar to 150 kgC during a growing season with 150 d. NMVOC fluxes can account for similar to 5% of total net carbon exchange (-3177 kgC) at the mire during the same period. NMVOC emissions are therefore a significant component in a local carbon budget for peatlands.
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| 5. |
- Börjesson, Gunnar, et al.
(author)
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A national landfill methane budget for Sweden based on field measurements, and an evaluation of IPCC models
- 2009
-
In: Tellus, Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 1600-0889 .- 0280-6509. ; 61:2, s. 424-435
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Journal article (peer-reviewed)abstract
- Seven Swedish landfills were investigated from 2001 to 2003. On each landfill, a measure of the total methane production was calculated from data on: (1) methane emissions (leakage); (2) methane oxidation and (3) from gas recovery. Methane emissions were determined via a tracer gas (N2O) release-based remote sensing method. N2O and CH4 were measured with an Fourier Transform infrared detector at a distance of more than 1 km downwind from the landfills. Methane oxidation in the landfill covers was measured with the stable carbon isotope method. The efficiency in gas recovery systems proved to be highly variable, but on an average, 51% of the produced landfill gas was captured. A first-order decay model, based on four fractions (waste from households and parks, sludges and industrial waste), showed that the use of a degradable organic carbon fraction (DOCf) value of 0.54, in accordance with the default value for DOCf of 0.50 in the latest IPCC model, gave an emission estimate similar to the official national reports.
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| 6. |
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| 7. |
- Freud, E., et al.
(author)
-
Anthropogenic aerosol effects on convective cloud microphysical properties in southern Sweden
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:2, s. 286-297
-
Journal article (peer-reviewed)abstract
- In this study, we look for anthropogenic aerosol effects in southern Scandinavia's clouds under the influence of moderate levels of pollution and relatively weak dynamic forcing. This was done by comparing surface aerosol measurements with convective cloud microphysical profiles produced from satellite image analyses. The results show that the clouds associated with the anthropogenic-affected air with high PM0.5, had to acquire a vertical development of similar to 3.5 km before forming precipitation-sized particles, compared to less than 1 km for the clouds associated with low PM0.5 air-masses. Additionally, a comparison of profiles with precipitation was done with regard to different potentially important parameters. For precipitating clouds the variability of the cloud thickness needed to produce the precipitation (Delta h(14)) is directly related to PM0.5 concentrations, even without considering atmospheric stability, the specific aerosol size distribution or the aerosols' chemical composition. Each additional 1 mu g m(-3) of PM0.5 was found to increase Delta h(14) by similar to 200-250 m. Our conclusion is that it is indeed possible to detect the effects of anthropogenic aerosol on the convective clouds in southern Scandinavia despite modest aerosol masses. It also emphasizes the importance of including aerosol processes in climate-radiation models and in numerical weather prediction models.
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| 8. |
- Hermann, M, et al.
(author)
-
Submicrometer aerosol particle distributions in the upper troposphere over the mid-latitude North Atlantic - Results from the third route of 'CARIBIC'
- 2008
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:1, s. 106-117
-
Journal article (peer-reviewed)abstract
- Particle number and mass concentrations of submicrometer aerosol particles were determined for the upper troposphere over the mid-latitude North Atlantic within the Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container project (CARIBIC, http://www.caribic-atmospheric.com). Between May 2001 and April 2002, 22 flights from Germany to the Caribbean were conducted using an automated measurement container on a B767 passenger aircraft. Spatial and seasonal probability distributions for ultrafine and Aitken mode particles as well as mass concentrations of particulate sulphur in 8-12 km altitude are presented. High particle number concentrations (mostly 2500-15 000 particles cm(-3) STP) are particularly found in summer over the western North Atlantic Ocean close to the North American continent. The distributions together with an analysis of particle source processes show that deep vertical transport is the dominant process leading to most of the events with high particle number concentrations (greater than or similar to 8000 particles cm(-3) STP) for ultrafine particles as well as for Aitken mode particles. This study emphasizes the importance of deep vertical transport and cloud processing for the concentration of aerosol particles in the upper troposphere.
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| 9. |
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| 10. |
- Lindroth, Anders
(author)
-
Foreword
- 2007
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59:5, s. 787-787
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Journal article (other academic/artistic)
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| 11. |
- Svenningsson, Birgitta, et al.
(author)
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Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland-forest mosaic
- 2008
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60, s. 353-364
-
Journal article (pop. science, debate, etc.)abstract
- An analysis of particle formation (PF) events over a subarctic mire in northern Sweden was performed, based on number size distributions of atmospheric aerosol particles (10-500 nm in diameter) and ions (0.4-40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005- September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis concentrates on calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm/h) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions repeated particle formation events were observed within one day, with differences in onset time of a few hour. These high growth rates were only observed when the condensation sink was higher than 0.001 s-1.
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| 12. |
- Swietlicki, Erik, et al.
(author)
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Hygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments : a review
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 432-469
-
Research review (peer-reviewed)abstract
- The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the size-resolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.
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| 13. |
- Thum, T., et al.
(author)
-
Spring initiation and autumn cessation of boreal coniferous forest CO2 exchange assessed by meteorological and biological variables
- 2009
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 61:5, s. 701-717
-
Journal article (peer-reviewed)abstract
- We studied the commencement and finishing of the growing season using different air temperature indices, the surface albedo, the chlorophyll fluorescence (Fv/Fm) and the carbon dioxide (CO2) tropospheric concentration, together with eddy covariance measurements of CO2 flux. We used CO2 flux data from four boreal coniferous forest sites covering a wide latitudinal range, and CO2 concentration measurements from Sammaltunturi in Pallas. The CO2 gas exchange was taken as the primary determinant for the growing season to which other methods were compared. Indices based on the cumulative temperature sum and the variation in daily mean temperature were successfully used for approximating the start and cessation of the growing season. The beginning of snow melt was a successful predictor of the onset of the growing season. The chlorophyll fluorescence parameter Fv/Fm and the CO2 concentration were good indicators of both the commencement and cessation of the growing season. By a derivative estimation method for the CO2 concentration, we were also able to capture the larger-scale spring recovery. The trends of the CO2 concentration and temperature indices at Pallas/Sammaltunturi were studied over an 11-yr time period, and a significant tendency towards an earlier spring was observed. This tendency was not observed at the other sites.
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| 14. |
- Delmas, RJ, et al.
(author)
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Bomb-test Cl-36 measurements in Vostok snow (Antarctica) and the use of Cl-36 as a dating tool for deep ice cores
- 2004
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 56:5, s. 492-498
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Journal article (peer-reviewed)abstract
- A large pulse of atmospheric Cl-36 generated by a limited number of nuclear tests peaked in the late 1950s to early 1960s. The corresponding enhanced Cl-36 deposition is seen in various glaciological archives in the Northern Hemisphere. The profile of the bomb spike recorded in firn layers at Vostok Station, central East Antarctica. has been measured by employing accelerator mass spectrometry (AMS). The records obtained front two well-dated data sets collected in snow pits in 1997 and 1998 show a broad Cl-36 peak, beginning as early as the 1940s and reaching its maximum in the 1960s. The signal is followed by a long-lasting tail up to the surface. This pattern is totally unexpected. We show that the results, unlike the Greenland data, can be explained by a mobility of HCl in the Antarctic firn. This experiment demonstrates the instability of gaseous Cl- deposits. a phenomenon which has important implications for the use of natural cosmogenic Cl-36 radionuclides as a reliable dating tool for deep ice cores from low-accumulation areas. However, during glacial times, under favourable atmospheric chemistry conditions this dating method may still be applicable. Snow metamorphism and ventilation are assumed to be the two main physical processes responsible for the observed patterns.
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| 15. |
- Grelle, A., et al.
(author)
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Large carbon-sink potential by Kyoto forests in Sweden - A case study on willow plantations
- 2007
-
In: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59:5, s. 910-918
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Journal article (peer-reviewed)abstract
- Fluxes of CO were measured in a 75-ha short-rotation willow plantation at Enkoping, central Sweden. The plantation was irrigated with wastewater for fertilization and water-filtering purposes. The harvested biomass was used locally for combined heat and power production. The plantation was a sink of ca. 8 tonnes C ha(-1) during 2003, of which ca. 50% was estimated to be attributed to fertilization. Biomass increment by shoot growth was 5 tonnes C ha-1 during the same year. Belowground carbon allocation was estimated to 3 tonnes C ha(-1) yr(-1) by a model that relates carbon allocation to shoot growth. Thus, the ecosystem carbon balance was closed by these estimations. The carbon uptake by the willow plantation was 5.5 times as high compared to a normally managed spruce forest, but only half as high as from an experimental, well-roanaged willow plantation in the same region. This illustrates the vast potential of short-rotation willow plantations for CO2 uptake from the atmosphere.
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| 16. |
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| 17. |
- Kristensson, Adam, et al.
(author)
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Characterization of New Particle Formation Events at a Background Site in Southern Sweden: Relation to Air Mass History
- 2008
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 330-344
-
Journal article (peer-reviewed)abstract
- Particle formation events were analysed from aerosol number size distribution data collected at a background station in southern Sweden between February 2001 and May 2004. Events occurred on about 36% of all days and were favoured by high global radiation values. The clearest events (class I, 20% of all days) were observed when the formation rate of activated hypothetical clusters around 1 nm diameter, J(1) was higher than 10((180*CondS-0.60)), where CondS is the condensation sink (in s(-1)). The median condensable vapour concentration, observed formation rate at 3 nm, and growth rate during class I events were 3.0 x 10(7) cm(-3), 1.1 cm(-3) s(-1) and 2.1 nm h(-1), respectively. On 7% of all days, it was possible to observe growth of the newly formed particles exceeding 30 nm geometric mean diameter during event days in the evening, which is important for the regional particle population, and thereby the climate. A trajectory analysis revealed that cleaner air masses were relatively more important for the contribution of Aitken mode particles than polluted ones. Class I events were registered on 36% of all days when trajectories had passed over the open sea, indicating that ship traffic can contribute to particle formation and growth.
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| 18. |
- Kulmala, Liisa, et al.
(author)
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H2O and CO2 fluxes at the floor of a boreal pine forest
- 2008
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:2, s. 167-178
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Journal article (peer-reviewed)abstract
- We measured H2O and CO2 fluxes at a boreal forest floor using eddy covariance (EC) and chamber methods. Maximum evapotranspiration measured with EC ranged from 1.5 to 2.0 mmol m(-2) s(-1) while chamber estimates depended substantially on the location and the vegetation inside the chamber. The daytime net CO2 exchange measured with EC (0-2 mu mol m(-2) s(-1)) was of the same order as measured with the chambers. The nocturnal net CO2 exchange measured with the chambers ranged from 4 to 7 mu mol m(-2) s(-1) and with EC from similar to 4 to similar to 5 mu mol m(-2) s(-1) when turbulent mixing below the canopy was sufficient and the measurements were reliable. We studied gross photosynthesis by measuring the light response curves of the most common forest floor species and found the saturated rates of photosynthesis (P-max) to range from 0.008 (mosses) to 0.184 mu mol g(-1) s(-1) (blueberry). The estimated gross photosynthesis at the study site based on average leaf masses and the light response curves of individual plant species was 2-3 mu mol m(-2) s(-1). At the same time, we measured a whole community with another chamber and found maximum gross photosynthesis rates from 4 to 7 mu mol m(-2) s(-1).
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| 19. |
- Kulmala, Markku, et al.
(author)
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Overview of the biosphere-aerosol-cloud-climate interactions (BACCI) studies
- 2008
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 300-317
-
Research review (peer-reviewed)abstract
- Here we present research methods and results obtained by the Nordic Centre of Excellence Biosphere-Aerosol-Cloud-Climate Interactions (BACCI) between 1 January 2003 and 31 December 2007. The centre formed an integrated attempt to understand multiple, but interlinked, biosphere-atmosphere interactions applying inter and multidisciplinary approaches in a coherent manner. The main objective was to study the life cycle of aerosol particles and their importance on climate change. The foundation in BACCI was a thorough understanding of physical, meteorological, chemical and ecophysiological processes, providing a unique possibility to study biosphere-aerosol-cloud-climate interactions. Continuous measurements of atmospheric concentrations and fluxes of aerosol particles and precursors and, CO2/aerosol trace gas interactions in different field stations (e.g. SMEAR) were supported by models of particle thermodynamics, transport and dynamics, atmospheric chemistry, boundary layer meteorology and forest growth. The main progress was related to atmospheric new particle formation, existence of clusters, composition of nucleation mode aerosol particles, chemical precursors of fresh aerosol particles, the contribution of biogenic aerosol particles on the global aerosol load, transport, transformation and deposition of aerosol particles, thermodynamics related to aerosol particles and cloud droplets, and the microphysics and chemistry of cloud droplet formation.
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| 20. |
- Lagergren, Fredrik, et al.
(author)
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Biophysical controls on CO2 fluxes of three Northern forets based on long-term eddy covariance data.
- 2008
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 60:2, s. 143-152
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Journal article (peer-reviewed)abstract
- Abstract in UndeterminedSix to nine years of net ecosystem carbon exchange (NEE) data from forests in Hyytiala in Finland, Soro in Denmark and Norunda in Sweden were used to evaluate the interannual variation in the carbon balance. For half-monthly periods, average NEE was calculated for the night-time data. For the daytime data parameters were extracted for the relationship to photosynthetic active radiation (PAR). The standard deviation of the parameters was highest for Norunda where it typically was around 25% of the mean, while it was ca. 15% for Hyytiala and Soro. Temperature was the main controller of respiration and photosynthetic capacity in autumn, winter and spring but explained very little of the interannual variation in summer. A strong correlation between respiration and photosynthesis was also revealed. The start, end and length of the growing season were estimated by four different criteria. The start date could explain some of the variation in yearly total NEE and gross primary productivity (GPP) in Hyytiala and Soro, but the average maximum photosynthetic capacity in summer explained more of the variation in annual GPP for all sites than start, end or length of the growing season.
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| 21. |
- Launiainen, S, et al.
(author)
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Vertical variability and effect of stability on turbulence characteristics down to the forest floor of a pine forest.
- 2007
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In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59, s. 919-936
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Journal article (peer-reviewed)abstract
- Among the fundamental problems in canopy turbulence, particularly near the forest floor, remain the local diabatic effects and linkages between turbulent length scales and the canopy morphology. To progress on these problems, mean and higher order turbulence statistics are collected in a uniform pine forest across a wide range of atmospheric stability conditions using five 3-D anemometers in the subcanopy. The main novelties from this experiment are: (1) the agreement between second-order closure model results and measurements suggest that diabatic states in the layer above the canopy explain much of the modulations of the key velocity statistics inside the canopy except in the immediate vicinity of the trunk space and for very stable conditions. (2) The dimensionless turbulent kinetic energy in the trunk space is large due to a large longitudinal velocity variance but it is inactive and contributes little to momentum fluxes. (3) Near the floor layer, a logarithmic mean velocity profile is formed and vertical eddies are strongly suppressed modifying all power spectra. (4) A spectral peak in the vertical velocity near the ground commensurate with the trunk diameter emerged at a moderate element Reynolds number consistent with Strouhal instabilities describing wake production.
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| 22. |
- Lund, Magnus, et al.
(author)
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Annual CO2 balance of a temperate bog
- 2007
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In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59, s. 804-811
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Journal article (peer-reviewed)
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| 23. |
- Tunved, Peter, et al.
(author)
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The natural aerosol over Northern Europe and its relation to anthropogenic emissions - implications of important climate feedbacks
- 2008
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60 B:4, s. 473-484
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Journal article (peer-reviewed)abstract
- We use a recently developed parametrization to estimate the regional particle field in the summer time troposphere over Scandinavia that would result if the forest were the only source of particles. The calculated field is compared with available observational data. It is concluded that the needle leaf forest above 58 degrees N alone is capable of producing aerosol mass concentrations corresponding to 12-50% of today's values in the boundary layer over Scandinavia. We also demonstrate that the forest itself could produce up to 200 CCN per cubic centimetre on average over Scandinavia and further show that an increase in temperature by 5.8 degrees C compared to today's average temperature could increase this CCN population by 40%. The study shows that we are able to approximate the natural aerosol field resulting from biogenic emissions over the boreal forest in the northern hemispheric region. This information provide an important contribution in the evaluation of the climate effect caused by anthropogenic emissions of particles over the forest and also opens the possibility to better address the climate feedbacks believed to be associated with the boreal region.
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| 24. |
- Lundén, Jenny, et al.
(author)
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The vertical distribution of atmospheric DMS in the high Arctic summer
- 2010
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In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 62:3, s. 160-171
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Journal article (peer-reviewed)abstract
- The vertical structure of gas-phase dimethyl sulfide, DMS(g), in the high Arctic atmosphere is investigated during a summer season. The model results show that the near-surface DMS(g) concentration over open ocean is very variable both in time and space, depending on the local atmospheric conditions. Profiles over ocean have typically highest concentration near the surface and decrease exponentially with height. Over the pack-ice, the concentrations are typically lower and the vertical structure changes as the air is advected northward. Modeled DMS(g) maxima above the local boundary layer were present in about 3\% of the profiles found over the pack-ice. These maxima were found in association to frontal zones. Our results also show that DMS(g) can be mixed downward by turbulence into the local boundary layer and act as a local near--surface DMS(g) source over the pack-ice and may hence influence the growth of cloud condensation nuclei and cloud formation in the boundary layer. Profile observations are presented in support to the model results. They show that significant DMS(g) concentrations exist in the Arctic atmosphere at altitudes not to be expected when only considering vertical mixing in the boundary layer.
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| 25. |
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| 26. |
- Jonsell, Ulf, et al.
(author)
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Correlation between concentrations of acids and oxygen isotope ratios in polar surface snow caused by local redeposition
- 2007
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In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59:2, s. 326-335
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Journal article (peer-reviewed)abstract
- Investigation of centimeter-scale snow surface chemistry has been carried out at two polar sites with different site characteristics–in Dronning Maud Land, Antarctica and on the Greenland ice sheet, respectively. Large variations in both impurity content and stable oxygen isotope ratios (δ18O) were found on the submeter scale. δ18O and the concentration of nitrate correlated at both sites (r = 0.81 and 0.82, respectively). At the Antarctic site, δ18O is also correlated to concentrations of methanesulphonate (r = 0.84) and sulphate (r = 0.83) while no such correlation exists at the Greenland site. Instead, a strong anticorrelation (r = –0.85) between sulphate and methanesulphonate is found among the samples from the Greenland site. The ions correlating with δ18O at the two sites were probably deposited as acids. Our tentative explanation is that local redeposition of water vapour enriching the snow surface with the lighter isotopes is associated with simultaneous enhanced scavenging of the acids. The responsible process thereby significantly alters the chemical signals of the snow surface.
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| 27. |
- Devasthale, Abhay, et al.
(author)
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The vertical distribution of thin features over the Arctic analysed from CALIPSO observations : Part 1: Optically thin clouds
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:1, s. 77-85
-
Journal article (peer-reviewed)abstract
- Clouds play a crucial role in the Arctic climate system. Therefore, it is essential to accurately and reliably quantify and understand cloud properties over the Arctic. It is also important to monitor and attribute changes in Arctic clouds. Here, we exploit the capability of the CALIPSO-CALIOP instrument and provide comprehensive statistics of tropospheric thin clouds, otherwise extremely difficult to monitor from passive satellite sensors. We use 4 yr of data (June 2006-May 2010) over the circumpolar Arctic, here defined as 67-82 degrees N, and characterize probability density functions of cloud base and top heights, geometrical thickness and zonal distribution of such cloud layers, separately for water and ice phases, and discuss seasonal variability of these properties. When computed for the entire study area, probability density functions of cloud base and top heights and geometrical thickness peak at 200-400, 1000-2000 and 400-800 m, respectively, for thin water clouds, while for ice clouds they peak at 6-8, 7-9 and 400-1000 m, respectively. In general, liquid clouds were often identified below 2 km during all seasons, whereas ice clouds were sensed throughout the majority of the upper troposphere and also, but to a smaller extent, below 2 km for all seasons.
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| 28. |
- Hegg, Dean A., et al.
(author)
-
Measurements of black carbon aerosol washout ratio on Svalbard
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:5, s. 891-900
-
Journal article (peer-reviewed)abstract
- Simultaneous measurements of aerosol black carbon (BC) in both fresh snow and in air on Svalbard are presented. From these, washout ratios for BC are calculated and compared to sparse previous measurements of this metric in the arctic. The current ratios are significantly higher than previously found measured values. We argue that the degree of snow riming within the accretion zone can explain most of this difference. Using an analytical model of the scavenging process, BC scavenging efficiencies are estimated to lie in the range 0.25-0.5, comparable to measured values.
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| 29. |
- Jonsson, Anders, 1966-, et al.
(author)
-
Variations in pCO2 during summer in the surface water of an unproductive lake in northern Sweden
- 2007
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59:5, s. 797-803
-
Journal article (peer-reviewed)abstract
- Unproductive lakes are generally supersaturated with carbon dioxide (CO2) and emit CO2 to the atmosphere continuously during ice-free periods. However, temporal variation of the partial pressure of CO2 (pCO2) and thus of CO2 evasion to atmosphere is poorly documented. We therefore carried out temporally high-resolution (every 6 h) measurements of the pCO2 using an automated logger system in the surface water of a subarctic, unproductive, lake in the birch forest belt. The study period was June–September 2004. We found that the pCO2 showed large seasonal variation, but low daily variation. The seasonal variation was likely mainly caused by variations in input and mineralization of allochthonous organic matter. Stratification depth probably also influenced pCO2 of the surface water by controlling the volume in which mineralization of dissolved organic carbon (DOC) occurred. In lakes, with large variations in pCO2, as in our study lake a high (weekly) sampling intensity is recommended for obtaining accurate estimates of the evasion of CO2.
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| 30. |
- Karl, Matthias, et al.
(author)
-
A new flexible multicomponent model for the study of aerosol dynamics in the marine boundary layer
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:5, s. 1001-1025
-
Journal article (peer-reviewed)abstract
- A new sectional aerosol dynamics model, MAFOR, was developed with the focus to study nucleation in the marine boundary layer. Novel aspects of the model are (1) flexibility in the treatment of gas phase chemistry, (2) treatment of liquid phase chemistry, which can be extended according to needs and (3) simultaneous calculation of number and mass concentration distributions of a multicomponent aerosol as functions of time. Comparison with well-documented aerosol models (MONO32 and AEROFOR), a comprehensive data set on gas phase compounds, aerosol size distribution and chemical composition obtained during the AOE-96 (Arctic Ocean Expedition, 1996) was used to evaluate the model. Dimethyl sulphide decay during advection of an air parcel over the Arctic pack ice was well captured by the applied models and predicted concentrations of gaseous sulphuric acid and methane sulphonic acid range up to 1.0 x 10(6) cm(-3) and 1.8 x 10(6) cm(-3), respectively. Different nucleation schemes were implemented in MAFOR which allow the simulation of new particle formation. Modelled nucleation rates from sulphuric acid nucleation via cluster activation were up to 0.21 cm(-3) s(-1) while those from ion-mediated nucleation were below 10(-2) cm(-3) s(-1). Classical homogeneous binary and ternary nucleation theories failed to predict nucleation over the central Arctic Ocean in summer.
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| 31. |
- Sogacheva, L., et al.
(author)
-
New aerosol particle formation in different synoptic situations at Hyytiala, Southern Finland
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:4, s. 485-494
-
Journal article (peer-reviewed)abstract
- We examine the meteorological conditions favourable for new particle formation as a contribution to clarifying the responsible processes. Synoptic weather maps and satellite images over Southern Finland for 2003-2005 were examined, focusing mainly on air mass types, atmospheric frontal passages. and cloudiness. Arctic air masses are most favourable for new aerosol particle formation in the boreal forest. New particle formation tends to occur on days after passage of a cold front and on days without frontal passages. Cloudiness, often associated with frontal passages, decreases the amount of: solar radiation. reducing the growth of new particles. When cloud cover exceeds 3-4 octas, particle formation proceeds at a slower rate or does not occur at all. During 2003-2005, the conditions that favour particle formation Lit Hyytiala (Arctic air mass, post-cold-frontal passage or no frontal passage and cloudiness less than 3-4 octas) occur oil 198 d. On 105 (57%) of those days, new particle formation occurred, indicating that these meteorological conditions alone can favour, but are not sufficient for, new particle formation and growth. In contrast, 53 d (28%) were classified as undefined days; 30 d (15%) were non-event days, where no evidence of increasing particle concentration and growth has been noticed.
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| 32. |
- Tesche, Matthias, et al.
(author)
-
Optical and microphysical properties of smoke over Cape Verde inferred from multiwavelength lidar measurements
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:4, s. 677-694
-
Journal article (peer-reviewed)abstract
- Lidar measurements of mixed dust/smoke plumes over the tropical Atlantic ocean were carried out during the winter campaign of SAMUM-2 at Cape Verde. Profiles of backscatter and extinction coefficients, lidar ratios, and Angstrom exponents related to pure biomass-burning aerosol from southern West Africa were extracted from these observations. Furthermore, these findings were used as input for an inversion algorithm to retrieve microphysical properties of pure smoke. Seven measurement days were found suitable for the procedure of aerosol-type separation and successive inversion of optical data that describe biomass-burning smoke. We inferred high smoke lidar ratios of 87 +/- 17 sr at 355 nm and 79 +/- 17 sr at 532 nm. Smoke lidar ratios and Angstrom exponents are higher compared to the ones for the dust/smoke mixture. These numbers indicate higher absorption and smaller sizes for pure smoke particles compared to the dust/smoke mixture. Inversion of the smoke data set results in mean effective radii of 0.22 +/- 0.08 mu m with individual results varying between 0.10 and 0.36 mu m. The single-scattering albedo for pure biomass-burning smoke was found to vary between 0.63 and 0.89 with a very low mean value of 0.75 +/- 0.07. This is in good agreement with findings of airborne in situ measurements which showed values of 0.77 +/- 0.03. Effective radii from the inversion were similar to the ones found for the fine mode of the in situ size distributions.
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| 33. |
- Tesche, Matthias, et al.
(author)
-
Profiling of Saharan dust and biomass-burning smoke with multiwavelength polarization Raman lidar at Cape Verde
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:4, s. 649-676
-
Journal article (peer-reviewed)abstract
- Extensive lidar measurements of Saharan dust and biomass-burning smoke were performed with one airborne and three ground-based instruments in the framework of the second part of the SAharan Mineral dUst experiMent (SAMUM-2a) during January and February of 2008 at Cape Verde. Further lidar observations with one system only were conducted during May and June of 2008 (SAMUM-2b). The active measurements were supported by Sun photometer observations. During winter, layers of mineral dust from the Sahara and biomass-burning smoke from southern West Africa pass Cape Verde on their way to South America while pure dust layers cross the Atlantic on their way to the Caribbean during summer. The mean 500-nm aerosol optical thickness (AOT) observed during SAMUM-2a was 0.35 +/- 0.18. SAMUM-2a observations showed transport of pure dust within the lowermost 1.5 km of the atmospheric column. In the height range from 1.5 to 5.0 km, mixed dust/smoke layers with mean lidar ratios of 67 +/- 14 sr at 355 and 532 nm, respectively, prevailed. Within these layers, wavelength-independent linear particle depolarization ratios of 0.12-0.18 at 355, 532, and 710 nm indicate a large contribution (30-70%) of mineral dust to the measured optical properties. Angstrom exponents for backscatter and extinction of around 0.7 support this finding. Mean extinction coefficients in the height range between 2 and 4 km were 66 +/- 6 Mm(-1) at 355 nm and 48 +/- 5 Mm(-1) at 532 nm. Comparisons with airborne high-spectral-resolution lidar observations show good agreement within the elevated layers. 3-5 km deep dust layers where observed during SAMUM-2b. These layers showed optical properties similar to the ones of SAMUM-1 in Morocco with a mean 500-nm AOT of 0.4 +/- 0.2. Dust extinction coefficients were about 80 +/- 6 Mm(-1) at 355 and 532 nm. Dust lidar ratios were 53 +/- 10 sr at 355 and 532 nm, respectively. Dust depolarization ratios showed an increase with wavelength from 0.31 +/- 0.10 at 532 nm to 0.37 +/- 0.07 at 710 nm.
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| 34. |
- Vogt, Matthias, et al.
(author)
-
Seasonal and diurnal cycles of 0.25–2.5 μm aerosol fluxes over urban Stockholm, Sweden
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:5, s. 935-951
-
Journal article (peer-reviewed)abstract
- Size resolved aerosol and gas fluxes were measured in Stockholm from 1 April 2008 to 15 April 2009 over both urban and green sectors. CO2 and H2O fluxes peaked in daytime for all seasons. CO2 concentrations peaked in winter. Due to vegetation influence the CO2 fluxes had different diurnal cycles and magnitude in the two sectors. In the urban sector, CO2 fluxes indicated a net source. The sector dominated by residential areas and green spaces had its highest aerosol fluxes in winter. In spring, super micrometer concentrations for both sectors were significantly higher, as were the urban sector rush hour fluxes. The submicrometer aerosol fluxes had a similar diurnal pattern with daytime maxima for all seasons. This suggests that only the super micrometer aerosol emissions are dependent on season. During spring there was a clear difference in super micrometer fluxes between wet and dry streets. Our direct flux measurements have improved the understanding of the processes behind these aerosol emissions. They support the hypothesis that the spring peak in aerosol emissions are due to road dust, produced during the winter, but not released in large quantities until the roads dry up during spring, and explain why Stockholm has problems meeting the EU directive for aerosol mass (PM10).
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| 35. |
- Fuzzi, S., et al.
(author)
-
The Po Valley Fog Experiment 1989
- 1992
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 44:5, s. 448-468
-
Journal article (peer-reviewed)abstract
- An outline is presented here of the Po Valley Fog Experiment 1989, carried out within the EUROTRAC‐GCE project. This experiment is a joint effort by several European research groups from 5 countries. The physical and chemical behaviour of the fog multiphase system was studied experimentally following the temporal evolution of the relevant chemical species in the different phases (gas, droplet, interstitial aerosol) and the evolution of micrometeorological and microphysical conditions, from the pre‐fog situation through the whole fog evolution, to the post‐fog period. Some general results, useful for describing the general features of the fog system, are presented here, while specific scientific questions on the different processes taking place within the system itself will be addressed in other companion papers of this same issue.
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| 36. |
- Martinsson, Bengt G., et al.
(author)
-
Elemental composition of fog interstitial particle size fractions and hydrophobic fractions related to fog droplet nucleation scavenging
- 1992
-
In: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 44:5, s. 593-603
-
Journal article (peer-reviewed)abstract
- The cloud nucleation scavenging process was studied during a joint campaign of the EUROTRAC sub‐project Ground‐based Cloud Experiment. It was found that the particle size has a strong influence on the partitioning of particles between the cloud droplet and the interstitial aerosol reservoirs. A new aerosol sampling unit, the relative humidity processing system, was employed for the extraction of particles with a low growth‐ability with respect to increased relative humidity. The system supplied tracer elements on the particle growth‐ability. These elements could be used to identify a factor related to particle hygroscopic properties, which was in effect as a selector of cloud condensation nuclei.
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| 37. |
- Aamaas, Borgar, et al.
(author)
-
Elemental carbon deposition to Svalbard snow from Norwegian settlements and long-range transport
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:3, s. 340-351
-
Journal article (peer-reviewed)abstract
- The impact on snow pack albedo from local elemental carbon (EC) sources in Svalbard has been investigated for the winter of 2008. Highly elevated EC concentrations in the snow are observed around the settlements of Longyearbyen and Svea (locally > 1000 ng g(-1), about 200 times over the background level), while EC concentrations similar to the background level are seen around Ny-Alesund. Near Longyearbyen and Svea, darkened snow influenced by wind transported coal dust from open coal stockpiles is clearly visible from satellite images and by eye at the ground. As a first estimate, the reduction in snow albedo caused by local EC pollution from the Norwegian settlements has been compared to the estimated reduction caused by long-range transported EC for entire Svalbard. The effect of local EC from Longyearbyen, Svea and all Norwegian settlements are estimated to 2.1%, 7.9% and 10% of the total impact of EC, respectively. The EC particles tend to stay on the surface during melting, and elevated EC concentrations due to the spring melt was observed. This accumulation of EC enhances the positive albedo feedbacks. The EC concentrations were observed to be larger in metamorphosed snow than in fresh snow, and especially around ice lenses.
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| 38. |
- Andersson, Camilla, 1979-, et al.
(author)
-
Interannual variation and trends in air pollution over Europe due to climate variability during 1958–2001 simulated with a regional CTM coupled to the ERA40 reanalysis
- 2007
-
In: Tellus. Series B, Chemical and physical meteorology. - Stockholm : Tellus. - 0280-6509 .- 1600-0889. ; 59, s. 77-98
-
Journal article (peer-reviewed)abstract
- A three-dimensional Chemistry Transport Model was used to study the meteorologically induced interannual variability and trends in deposition of sulphur and nitrogen as well as concentrations of surface ozone (O3), nitrogen dioxide (NO2) and particulate matter (PM) and its constituents over Europe during 1958–2001. The model was coupled to the meteorological reanalysis ERA40, produced at the European Centre for Medium-range Weather Forecasts. Emissions and boundary conditions of chemical compounds and PM were kept constant at present levels. The average European interannual variation, due to meteorological variability, ranges from 3% for O3, 5%for NO2, 9% for PM, 6–9% for dry deposition, to about 20% for wet deposition of sulphur and nitrogen. For the period 1979–2001 the trend in ozone, due to climate variability is increasing in central and southwestern Europe and decreasing in northeastern Europe, the trend in NO2 is approximately opposite. The trend in PM is positive in eastern Europe. There are negative trends in wet deposition in southwestern and central Europe and positive trends in dry deposition overall. A bias in ERA40 precipitation could be partly responsible for the trends. The variation and trends need to be considered when interpreting measurements and designing measurement campaigns.
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| 39. |
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| 40. |
- Blasing, T.J, et al.
(author)
-
The annual cycle of fossil-fuel carbon dioxide emissions in the United States
- 2005
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 57:2, s. 107-115
-
Journal article (peer-reviewed)abstract
- Time-series of estimated monthly carbon dioxide emissions from consumption of coal, petroleum and natural gas in the United States from 1981 to 2002 have been derived from energy consumption data. The data series for coal and natural gas each reveal a consistent seasonal pattern, with a winter peak for gas and two peaks (summer and winter) for coal. The annual cycle of total emissions has an amplitude of about 20 Tg-C, and is dominated by CO2 released from consumption of natural gas. Summation of the monthly estimates to obtain annual values reveals good agreement with other estimates of CO2 emissions. The varying proportions of CO2 emitted from each fuel type over the course of a year lead to an annual cycle in the carbon isotope ratio (δ13C), with a range of about 2 ‰. These monthly carbon emissions estimates should be helpful in understanding the carbon cycle by providing (1) monthly/seasonal input for carbon cycle models, (2) estimates of the annual cycle of the 13C isotope ratio in fossil-fuel CO2 emissions and (3) data at fine enough time intervals to investigate effects of seasonal climate variations and changes in seasonally dependent use patterns of certain appliances (e.g. air conditioners) on fossil-fuel carbon emissions.
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| 41. |
- Brandefelt, Jenny, et al.
(author)
-
Anthropogenic and biogenic winter sources of Arctic CO2 - a model study
- 2001
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 53:1, s. 10-21
-
Journal article (peer-reviewed)abstract
- Long-range transport of anthropogenic and biogenic CO2 to a remote site in the Arctic is studied. A limited area, off-line, Eulerian atmospheric transport model is used, and the results are compared to the observed CO2 concentration at the Ny-Alesund International Arctic Research and Monitoring Facility. Inventories of anthropogenic CO2 emissions and estimates of biogenic CO2 emissions are used to investigate the respective impact of these emissions on Arctic CO2 variations during 4 winter months. A direct comparison of the modelled and observed concentrations reveals remarkably good timing in the modelled variations as compared to the observed variations for most of the time. The correlation of observed versus modelled CO2 concentration is significant at the 95% confidence level. The biogenic and the anthropogenic CO2 emissions are shown to have approximately equal influence on Arctic CO2 variations during winter. Europe is found to be the dominant source of anthropogenic CO2 Lit the monitoring station, while Siberia and Northern America have little influence on Arctic CO2. during the months studied. These results contradict Engardt and Holmen whose results indicate that the lower-Ob region in western Siberia has a large impact on Arctic CO2.
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| 42. |
- Coz Diego, Esther, et al.
(author)
-
Morphology and state of mixture of atmospheric soot aggregates during the winter season over Southern Asia-a quantitative approach
- 2011
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:1, s. 107-116
-
Journal article (peer-reviewed)abstract
- The atmospheric brown cloud phenomena characterized by a high content of soot and a large impact on the solar radiative heating especially affects the tropical Indian Ocean during the winter season. The present study focuses on morphological characteristics and state of mixture of soot aggregates during the winter season over India. Given are quantitative measures of size, morphology and texture on aggregates collected in air at two different sites: Sinhagad near Pune in India and Hanimaadhoo in Maldives. For the latter site two different synoptic patterns prevailed: advection of air from the Arabian region and from the Indian subcontinent, respectively. Aggregates collected at Sinhagad, were associated with open branched structures, characteristic of fresh emission and diameters between 220 and 460 nm. The Hanimaadhoo aggregates were associated with aged closed structures, smaller sizes (130-360 nm) and frequently contained inorganic inclusions. Those arriving from the Indian subcontinent were characterized by the presence of an additional organic layer that covered the aggregate structure. These organic coatings might be a reasonable explanation of the low average wash-out ratios of soot two to seven times lower than that of nss-SO(4)2- that have been reported for air flow arriving at Hanimaadhoo from the Indian subcontinent in winter.
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| 43. |
- Dal Maso, Miikka, et al.
(author)
-
Annual and interannual variation in boreal forest aerosol particle number and volume concentration and their connection to particle formation
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:4, s. 495-508
-
Journal article (peer-reviewed)abstract
- We investigated size-resolved submicrometre aerosol particle number and volume concentration time series as well as aerosol dynamic parameters derived front Differential Mobility Particle Sizer (DMPS) measurements at five background stations in the Nordic boreal forest area. The stations in question were Aspvreten, Hyytiala and Uto in Southern Finland and Sweden, and Varrio and Pallas in the Finnish Lapland. The objective Of Our investigation was to identify and quantity annual and interannual variation observable in the time series. We found that the total number and mass concentrations were touch lower at the Lapland stations than at the southern stations and that the total particle number was strongly correlated to particle formation event frequency. The annual total number concentration followed the annual distribution of particle formation events at the Southern stations but much less clearly at the Lapland stations. The volume concentration was highest during summer, in line with higher condensation growth rates: this is in line with the assumption that a large part of the particle volume is produced by oxidized plant emissions. The decrease of sulphate emissions in Europe was not visible in our data set. Aerosol dynamic parameters such as condensation sink, condensation sink diameter and the power law exponent linking coagulation losses and condensation sink are presented to characterize the submicron Nordic background aerosol.
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| 44. |
- Engvall, Ann-Christine, et al.
(author)
-
In-situ airborne observations of the microphysical properties of the Arctic tropospheric aerosol during late spring and summer
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 392-404
-
Journal article (peer-reviewed)abstract
- In-situ aerosol data collected in the Arctic troposphere during a three-week period in 2004 were analysed. The measurements took place during late spring, i.e., at the time of the year when the characteristics of the aerosol distribution change from being accumulation-mode dominated to being primarily of the Aitken-mode type, a process that previously has been observed in the boundary layer. To address the question whether this transition is also detectable in the free troposphere of an aircraft-measured data from the ASTAR 2004 campaign were analysed. In this study, we present vertically as well as temporally results from both ground-based and airborne measurements of the total number concentrations of particles larger than 10 and 260 nm. Aircraft-measured size distributions of the aerosol ranging from 20 to 2200 nm have been evaluated with regard to conditions in the boundary layer as well as in the free troposphere. Furthermore an analysis of the volatile fraction of the aerosol population has been performed both for the integrated and size-distributed results. From these investigations we find that the transition takes place in the entire troposphere.
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| 45. |
- Engvall, Ann-Christine, et al.
(author)
-
The radiative effect of an aged, internally mixed Arctic aerosol originating from lower-latitude biomass burning
- 2009
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 61:4, s. 677-684
-
Journal article (peer-reviewed)abstract
- Arctic-haze layers and their radiative effects have been investigated previously in numerous studies as they are known to have an impact on the regional climate. In this study, we report on an event of an elevated aerosol layer, notably consisting of high-absorbing soot particles, observed in the European Arctic free troposphere the 2007 April 14 during the ASTAR 2007 campaign. The ca. 0.5 km vertically thick aerosol layer located at an altitude of around 3 km had a particle-size distribution mode around 250 nm diameter. In this study, we quantify the radiative effect aerosol layers have on the Arctic atmosphere by using in situ observations. Measurements of particles size segregated temperature stability using thermal denuders, indicate that the aerosol in the optically active size range was chemically internally mixed. In the plume, maximum observed absorption and scattering coefficients were 3 x 10(-6) and 20 x 10(-6) m(-1), respectively. Observed microphysical and optical properties were used to constrain calculations of heating rates of an internally mixed aerosol assuming two different surface albedos that represent snow/ice covered and open ocean. The average profile resulted in a heating rate in the layer of 0.2 K d(-1) for the high-albedo case and 0.15 K d(-1) for the low albedo case. This calculated dependence on albedo based on actual observations corroborates previous numerical simulations. The heating within the plume resulted in a measurable signal shown as an enhancement in the temperature of a few tenths of a degree. Although the origin of the aerosol plume could not unambiguously be determined, the microphysical properties of the aerosol had strong similarities with previously reported biomass burning plumes. With a changing climate, short-lived pollutants such as biomass plumes may become more frequent in the Arctic and have important radiative effects at regional scale.
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| 46. |
- Fleischer, Siegfried, 1938-, et al.
(author)
-
Nitrogen cycling drives a strong within-soil CO2-sink
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - Oxford : Wiley-Blackwell. - 0280-6509 .- 1600-0889. ; 60:5, s. 782-786
-
Journal article (peer-reviewed)abstract
- For about three decades, it has not been possible to completely balance global carbon emissions into known pools. A residual (or 'missing') sink remains. Here evidence is presented that part of soil respiration is allocated into an internal soil CO2-sink localized to the saprophytic subsystem (roots excluded). The process occurs in forest, agricultural and grassland soils and is favoured by high N-deposition. Chemoautotrophic nitrification has a key role, and the most efficient internal CO2-sequestration occurs concurrently with lowest soil nitrate (NO3-) concentrations, despite considerable N-loading. Not until drastic N-supply occurs, does the CO2-sink successively breakdown, and nitrate concentrations increase, leading to NO3--leaching. Within-soil CO2-uptake seems to be of the same magnitude as the missing carbon sink. It may be gradually enforced by the ongoing input of nitrogen to the biosphere.
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| 47. |
- Hussein, Tareq, et al.
(author)
-
Observation of regional new particle formation in the urban atmosphere
- 2008
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:4, s. 509-521
-
Journal article (peer-reviewed)abstract
- Long-term measurements of fine particle number-size distributions were carried out over 9.5 yr (May 1997-December 2006), in the urban background atmosphere of Helsinki. The total number of days was 3528 with about 91.9% valid data. A new particle formation event (NPF) is defined if a distinct nucleation mode of aerosol particles is observed below 25 nm for several hours, and it shows a growth pattern. We observed 185 NPF events, 111 d were clear non-events and most of the days (around 83.5%) were undefined. The observed events were regional because they were observed at Hyytiala (250 km north of Helsinki). The events occurred most frequently during spring and autumn. The observed formation rate was maximum during the spring and summer (monthly median 2.87 cm(-3) s(-1)) and the modal growth rate was maximum during late summer and Autumn (monthly median 6.55 mm h(-1)). The events were observed around noon, and the growth pattern often continued on the following day. The observation of weak NPF events was hindered due to pre-existing particles from both local sources. It is clear that regional NPF events have a clear influence oil the dynamic behaviour of aerosol particles in the urban atmosphere.
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| 48. |
- Johansson, Elisabeth, et al.
(author)
-
Nitrous oxide exchanges with the atmosphere of a constructed wetland treating wastewater - Parameters and implications for emission factors
- 2003
-
In: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 55:3, s. 737-750
-
Journal article (peer-reviewed)abstract
- Static chamber measurements of N2O fluxes were taken during the 1998 and 1999 growth seasons in a Swedish constructed wetland receiving wastewater. The dominating plant species in different parts of the wetland were Lemna minor L., Typha latifolia L., Spirogyra sp. and Glyceria maxima (Hartm.) and Phalaris arundinacea (L.), respectively. There were large temporal and spatial variations in N2O fluxes, which ranged from consumption at -350 to emissions at 1791 mug N2O m(-2) h(-1). The largest positive flux occurred in October 1999 and the lowest in the middle of July 1999. The average N2O flux for the two years was 130 mug N2O m(-2) h(-1) (SD = 220). No significant differences in N2O fluxes were found between the years, even though the two growing seasons differed considerably with respect to both air temperature and precipitation. 15% of the fluxes were negative, showing a consumption of N2O. Consumption occurred on a few occasions at most measurement sites and ranged from 1-350 mug N2O m(-2) h(-1). 13-43% of the variation in N2O fluxes was explained by multiple linear regression analysis including principal components. Emission factors were calculated according to IPCC methods from the N2O fluxes in the constructed wetland. The calculated emission factors were always lower (0.02-0.27%) compared to the default factor provided by the IPCC (0.75%). Thus, direct application of the IPCC default factor may lead to overestimation of N2O fluxes from constructed wastewater-treating wetlands.
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| 49. |
- Jonsell, Ulf, et al.
(author)
-
Correlations between concentrations of acids andoxygen isotope ratios in polar surface snow
- 2007
-
In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59b, s. 326-335
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Journal article (peer-reviewed)abstract
- Investigation of centimeter-scale snow surface chemistry has been carried out at two polar sites with different site characteristics–in Dronning Maud Land, Antarctica and on the Greenland ice sheet, respectively. Large variations in both impurity content and stable oxygen isotope ratios ( δ18O) were found on the submeter scale. δ18 O and the concentration of nitrate correlated at both sites (r = 0.81 and 0.82, respectively). At the Antarctic site, δ18 O is also correlated to concentrations of methanesulphonate (r = 0.84) and sulphate (r = 0.83) while no such correlation exists at the Greenland site. Instead, a strong anticorrelation (r = –0.85) between sulphate and methanesulphonate is found among the samples from the Greenland site. The ions correlating with δ18 O at the two sites were probably deposited as acids. Our tentative explanation is that local redeposition of water vapour enriching the snow surface with the lighter isotopes is associated with simultaneous enhanced scavenging of the acids. The responsible process thereby significantly alters the chemical signals of the snow surface.
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