| 1. |
- Budhavant, Krishnakant B., et al.
(författare)
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Physico-chemical characterization and sink mechanism of atmospheric aerosols over South-west India
- 2020
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Ingår i: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 77:1-2, s. 17-33
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Tidskriftsartikel (refereegranskat)abstract
- The properties of the atmospheric aerosols depend on the source region and on the modifications that occur during their transport in the air. We have studied physical and chemical properties of aerosols along with their sink mechanism over two locations in southwest India, an urban site (Pune) and well-established climate observatory at Sinhagad (SINH), which represents rural and high altitude site. The ground-based measurements of aerosols, together with their radiative properties in this study have provided means to understand the observed variability and the impact on the aerosol radiative properties effectively over this region. The annual mean elemental carbon concentration (3.4 mu g m(- 3)) at Pune was observed about three times higher compared to SINH (1.3 mu g m(- 3)), indicating strong emissions of carbon-rich aerosols at the urban location. Aerosol optical properties were derived using the OPAC model which were used to compute the Aerosol radiative forcing (ARF) over both stations calculated using SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model shows pronounced seasonal variations due to changes in aerosol optical depth and single scattering albedo at both locations. The year-round ARF was 4-5 times higher over Pune (31.4 +/- 3.5 Wm(- 2)) compared to SINH (7.2 +/- 1.1 Wm(- 2)). The atmospheric heating rate due to aerosols shows a similar pattern as ARF for these locations. The heating was higher in the wintertime, similar to 0.9-1.6 K day(- 1) at Pune, and similar to 0.3-0.6 K day(- 1) at SINH. The estimated scavenging ratio was found high for NO3- and Ca.(2+). The wet deposition fluxes of Cl-, SO42-, Na+, Mg2+ were observed higher for SINH as compared to Pune, due to the high amount of rain received at SINH.
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| 2. |
- Drewnick, Frank, et al.
(författare)
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Measurement of ambient, interstitial, and residual aerosol particles on a mountaintop site in central Sweden using an aerosol mass spectrometer and a CVI
- 2007
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Ingår i: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 56:1, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- The Aerodyne aerosol mass spectrometer (Q-AMS) was coupled with a counterflow virtual impactor (CVI) for the first time to measure cloud droplet residuals of warm tropospheric clouds on Mt. Areskutan in central Sweden in July 2003. Operating the CVI in different operational modes generated mass concentration and species-resolved mass distribution data for non-refractory species of the ambient, interstitial, and residual aerosol. The ambient aerosol measurements revealed that the aerosol at the site was mainly influenced by long-range transport and regional photochemical generation of nitrate and organic aerosol components. Four different major air masses were identified for the time interval of the experiment. While two air masses that approached the site from northeastern Europe via Finland showed very similar aerosol composition, the other two air masses from polar regions and the British Islands had a significantly different composition. During cloud events the larger aerosol particles were found to be activated into cloud droplets. On a mass basis the activation cut-off diameter was approximately 150 nm for nitrate and organics dominated particles and 200 nm for sulfate dominated particles. Generally nitrate and organics were found to be activated into cloud droplets with higher efficiency than sulfate. While a significant fraction of the nitrate in ambient particles was organic nitrates or nitrogen-containing organic species, the nitrate found in the cloud droplet residuals was mainly ammonium nitrate. After passage of clouds the ambient aerosol size distribution had shifted to smaller particle sizes due to the predominantly activation of larger aerosol particles without a significant change in the relative composition of the ambient aerosol.
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| 3. |
- Harmens, H, et al.
(författare)
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Heavy metal concentrations in European mosses: 2000/2001 survey
- 2004
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Ingår i: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 49:1-3, s. 425-436
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Tidskriftsartikel (refereegranskat)abstract
- The heavy metals in mosses survey was originally established in 1980 as a joint Danish-Swedish initiative under the leadership of Angstromke Ruhling, Sweden and has, since then, been repeated at five-yearly intervals with an increasing number of countries and individuals participating. Twenty-eight European countries, almost 7000 sites and about 100 individuals have been involved in the most recent survey in 2000/2001. The survey provides data on concentrations of 10 heavy metals (arsenic, cadmium, chromium, copper, iron, lead, mercury, nickel, vanadium, zinc) in naturally growing mosses throughout Europe. The technique of moss analysis provides a surrogate measure of the spatial patterns of heavy metal deposition from the atmosphere to terrestrial systems, and is easier and cheaper than conventional precipitation analysis. The aims of the survey are to determine patterns of variation in the heavy metal concentration of mosses across Europe, identify the main polluted areas, produce regional maps and further develop the understanding of long-range transboundary pollution. As in previous surveys, there was an east/west decrease in heavy metal concentrations in mosses, related in particular to industrial emissions. Former industrial sites and historic mines accounted for the location of some high concentrations in areas without contemporary industries. Long-range transboundary transport appears to account for elevated concentrations of heavy metals in areas without emission sources, such as lead in southern Scandinavia (presumably from emission sources elsewhere in Europe).
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| 4. |
- Hultquist, Gunnar, et al.
(författare)
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Catalysed self-cleaning of air on the earth's surface
- 2006
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Ingår i: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 55:2, s. 131-146
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Tidskriftsartikel (refereegranskat)abstract
- Generally, it is assumed that UV-light, high temperature or reactive molecules like O-3 and OH are needed to activate gas reactions in air. In consequence, the catalytic activity on natural materials such as sand and soil on the earth's surface is assumed to be insignificant. We have measured O-2-dissociation rates on natural quartz sand at 40 degrees C and compared these with O-2-dissociation rates near 500 degrees C on materials with well-known catalytic activity. In terms of probabilities for dissociation of impinging O-2-molecules the measured rates are in the 10(-12)-10(-4) range. We have also measured dissociation rates of H-2 and N-2, water-formation from H-2 and O-2 mixtures, exchange of N between N-2, NO (x) and a breakdown of HNO3, NO2 and CH4 on natural quartz sand at 40 degrees C. The measured rates together with an effective global land area have been used to estimate the impact of thermodynamically driven reactions on the earth's surface on the global atmospheric budgets of H-2, NO2 and CH4. The experimental data on natural quartz sand together with data from equilibrium calculations of air suggest that an expected increase in anthropogenic supply of air pollutants, such as NO (x) or other reactive nitrogen compounds, hydrogen and methane, will be counter-acted by catalysis on the earth's surface. On the other hand, at Polar Regions and boreal forests where the reactive nitrogen concentration is below equilibrium, the same catalytic effect activates formation of bio-available nitrogen compounds from N-2, O-2 and H2O.
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| 5. |
- Perrin, A., et al.
(författare)
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Molecular line parameters for the "MASTER" (Millimeter Wave Acquisitions for Stratosphere/Troposphere Exchange Research) database
- 2005
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Ingår i: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 51:2, s. 161-205
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the upper troposphere/lower stratosphere (UTLS) region of the earth's atmosphere, ESA/ESTEC (European space agency) is considering the opportunity to develop the spaceborne limb sounding millimeter sensor "MASTER" (millimeter wave acquisitions for stratosphere/troposphere exchange research). This instrument is part of the "atmospheric composition explorer for chemistry and climate interactions" (ACECHEM) project. In addition, ESA/ESTEC is developing the "MARSCHALS" (millimeter-wave airborne receiver for spectroscopic characterization of atmospheric limb sounding) airborne instrument which will demonstrate the feasibility of MASTER. The present paper describes the line-by-line database which was generated in order to meet at best the needs of the MASTER (or MARSCHALS) instrument. The linelist involves line positions, line intensities, line broadening and line shift parameters in the 294-305, 316-325, 342-348, 497-506 and 624-626 GHz spectral microwindows. This database was first generated for the target molecules for MASTER (H2O, O3, N2O, CO, O2, HNO3, HCl, ClO, CH3Cl, BrO). In addition, ten additional molecules (SO2, NO2, OCS, H2CO, HOCl, HCN, H2O2, COF2, HO2 and HOBr) had also to be considered in the database as "possible interfering species" for the retrieval of the target molecules of MASTER. The line parameters were derived, depending on their estimated accuracy, (i) from a combination of spectral parameters included in the JPL and HITRAN catalogs (ii) from data taken into the literature or (iii) using data obtained through experimental measurements (and/or) calculations performed during the present study.
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| 6. |
- Pommer, Linda, et al.
(författare)
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The influence of O3, relative humidity, NO and NO2 on the oxidation of α-pinene and Δ3-carene
- 2004
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Ingår i: Journal of Atmospheric Chemistry. - Dordrecht : Kluwer Academic Publishers. - 0167-7764 .- 1573-0662. ; 48:2, s. 173-189
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Tidskriftsartikel (refereegranskat)abstract
- Upto 13% of α-pinene and δ3-carene had reacted after 213 s in this dark experimental set-up, where O3, NO and NO2 were mixed with terpenes at different relative humidities (RHs). The different experiments were planned according to an experimental design, where O3, NO2, NO, RH and reaction time were varied between high and low settings (25 and 75 ppb, 15 and 42%, 44 and 213 s). An increased amount of α-pinene and δ3-carene reacted in the chamber was observed, when the level of O3, NO and reaction time was increased and RH was decreased. In the study, it was found that different interactions affected the amount of terpene reacted as well. These interactions were between O3 and NO, O3 and reaction time, NO and RH, and between NO and reaction time.
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| 7. |
- Wittbom, C., et al.
(författare)
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Effect of solubility limitation on hygroscopic growth and cloud drop activation of SOA particles produced from traffic exhausts
- 2018
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Ingår i: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 75:4, s. 359-383
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Tidskriftsartikel (refereegranskat)abstract
- Hygroscopicity measurements of secondary organic aerosol (SOA) particles often show inconsistent results between the supersaturated and subsaturated regimes, with higher activity as cloud condensation nucleus (CCN) than indicated by hygroscopic growth. In this study, we have investigated the discrepancy between the two regimes in the Lund University (LU) smog chamber. Various anthropogenic SOA were produced from mixtures of different precursors: anthropogenic light aromatic precursors (toluene and m-xylene), exhaust from a diesel passenger vehicle spiked with the light aromatic precursors, and exhaust from two different gasoline-powered passenger vehicles. Three types of seed particles were used: soot aggregates from a diesel vehicle, soot aggregates from a flame soot generator and ammonium sulphate (AS) particles. The hygroscopicity of seed particles with condensed, photochemically produced, anthropogenic SOA was investigated with respect to critical supersaturation (sc) and hygroscopic growth factor (gf) at 90% relative humidity. The hygroscopicity parameter κ was calculated for the two regimes: κsc and κgf, from measurements of sc and gf, respectively. The two κ showed significant discrepancies, with a κgf /κsc ratio closest to one for the gasoline experiments with ammonium sulphate seed and lower for the soot seed experiments. Empirical observations of sc and gf were compared to theoretical predictions, using modified Köhler theory where water solubility limitations were taken into account. The results indicate that the inconsistency between measurements in the subsaturated and supersaturated regimes may be explained by part of the organic material in the particles produced from anthropogenic precursors having a limited solubility in water.
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| 8. |
- Kultti, Anne, 1976, et al.
(författare)
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Bring Your Own Toy: Socialisation of Two-Year-Olds Through Tool-Mediated Activities in an Australian Early Childhood Education Context
- 2015
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Ingår i: Early Childhood Education Journal. - : Springer Science and Business Media LLC. - 1082-3301 .- 1573-1707. ; 43:5, s. 367-376
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Tidskriftsartikel (refereegranskat)abstract
- The study focuses on how young children are socialised in early childhood education practice in activities with and around toys. A premise of this study is the theoretical notion of sociocultural theory that people do things with artefacts and other cultural tools, and tools do things with people. This is captured in the unit of analysis, tool-mediated activities. Two activities, documented by video observations, are analysed. The empirical data are illustrated through images and transcripts, and the analysis is grounded on an interactional approach. The analysis illustrates that play activities in this practice offer opportunities to use toys in individual ways. Yet, the toys also provide ways of participating in activities together with other children when there is a common artefact within the activity, for instance a parking lot for driving cars on. Therefore, even when playing individually and with individual toys, children can participate in a joint activity. How toys mediated knowledge and practice on individual, interpersonal, and institutional planes is discussed. The findings suggest that toys support communication before children have developed verbal language skills and that certain types of tools facilitate both individual and collective use.
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| 9. |
- Tusman, Gerardo, et al.
(författare)
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Model fitting of volumetric capnograms improves calculations of airway dead space and slope of phase III
- 2009
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Ingår i: Journal of clinical monitoring and computing. - : Springer Science and Business Media LLC. - 1387-1307 .- 1573-2614. ; 23:4, s. 197-206
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Tidskriftsartikel (refereegranskat)abstract
- Background This study assessed the performance of a Functional Approximation based on a Levenberg-Marquardt Algorithm (FA-LMA) to calculate airway dead space (VDaw) and the slope of phase III (S III) from capnograms. Methods We performed mathematical simulations to test the effect of noises on the calculation of VDaw and S III. Data from ten mechanically ventilated patients at 0, 5 and 10 cmH2O of PEEP were also studied. FA-LMA was compared with the traditional Fowler’s method (FM). Results Simulations showed that: (1) The FM determined VDaw with accuracy only if the capnogram approximated a symmetrical curve (S III = 0). When capnograms became asymmetrical (S III > 0), the FM underestimated VDaw (−3.1% to −0.9%). (2) When adding noises on 800 capnograms, VDaw was underestimated whenever the FM was used thereby creating a bias between −5.54 and −1.28 ml at standard deviations (SD) of 0.1–1.8 ml (P < 0.0001). FA-LMA calculations of VDaw were close to the simulated values with the bias ranging from −0.21 to 0.16 ml at SD from 0.1 to 0.4 ml. The FM overestimated S III and showed more bias (0.0041–0.0078 mmHg/ml, P < 0.0001) than the FA-LMA (0.0002–0.0030 mmHg/ml). When calculating VDaw from patients, variability was less with the FA-LMA leading to mean variation coefficients of 0.0102, 0.0111 and 0.0123 compared to the FM (0.0243, 0.0247 and 0.0262, P < 0.001) for 0, 5 and 10 cmH2O of PEEP, respectively. The FA-LMA also showed less variability in S III with mean variation coefficients of 0.0739, 0.0662 and 0.0730 compared to the FM (0.1379, 0.1208 and 0.1246, P < 0.001) for 0, 5 and 10 cmH2O of PEEP, respectively. Conclusions The Functional Approxi- mation based on a Levenberg-Marquardt Algorithm showed less bias and dispersion compared to the traditional Fowler’s method when calculating VDaw and S III.
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