| 1. |
- Bower, K. N., et al.
(författare)
-
ACE-2 HILLCLOUD. An overview of the ACE-2 ground-based cloud experiment
- 2000
-
Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 52:2, s. 750-778
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 2. |
- Mentes, B., et al.
(författare)
-
Ion-beam thermography analysis of the H2SO4-(NH4)2SO4 system in aerosol samples
- 2000
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 168:4, s. 533-542
-
Tidskriftsartikel (refereegranskat)abstract
- Ion-beam thermography (IBT) is used to determine the chemical composition of atmospheric aerosols. The aerosols are analyZed by a combination of four ion-beam techniques PIXE, PESA, pNRA and cPESA during thermography. These techniques monitor the concentrations of the available elements during the stepwise heating of the sample. For each element a thermogram, i.e., the concentration vs. temperature, is obtained. Vaporization of chemical compounds generated during heating will result in a decrease in concentration in the thermograms at temperatures that are characteristic for the compounds. The compounds are identified by the stoichiometric ratios and the characteristic vaporization temperatures (CVT). This paper deals with the analysis of five different laboratory-produced aerosols with the following compositions: (NH4)2SO4, (NH4)1.5H0.5SO4, NH4HSO4, (NH4)0.5H1.5SO4 and H2SO4. All compounds were readily separated with respect to response in IBT analysis and the amount of water bound to the two most acidic compounds could be quantified.
|
|
| 3. |
- Mentes, B., et al.
(författare)
-
Vaporisation characteristics and detection limits of ion beam thermography
- 1999
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 150:1-4, s. 136-143
-
Tidskriftsartikel (refereegranskat)abstract
- Analytical properties of the chemical speciation method, Ion beam thermography (IBT), have been investigated. IBT combines the multi-elemental ion beam techniques PIXE, PESA, pNRA and cPESA with thermography. During thermography the sample temperature is gradually increased, causing vaporisation of chemical compounds at specific temperatures and the sample at the same time undergoes analysis by the above-mentioned techniques. The characteristic vaporisation temperature (CVT) and the stoichiometric relations between the elements vaporised at that temperature, identify the chemical compounds. This work describes the reproducibility of the method, the dependence of the rate of temperature increase, the dependence of the sample thickness and the influence from aerosol particle size on the CVT. In addition the minimum detectable mass changes for IBT analysis of marine and continental aerosols were estimated by calculation for major and minor elements.
|
|
| 4. |
- Papaspiropoulos, G., et al.
(författare)
-
High sensitivity elemental analysis methodology for upper tropospheric aerosol
- 1999
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 150:1-4, s. 356-362
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, a sampling and analysis tool for aerosol particles has been developed. Its purpose is to characterize upper tropospheric aerosols, where concentrations are low. Since measurements will be made from an airplane, a time resolution of one hour is desirable. These conditions require efficient sampling and analysis with low detection limits. To accomplish this, our sampler uses impaction, concentrating the aerosol deposit on a small area. The impactor has 14 parallel sampling lines which are used sequentially to achieve the time resolution. The elemental analysis is done with Particle-Induced X-ray Emission (PIXE), profiting from its high absolute sensitivity. The aerosol is expected to contains primarily sulphur (S) and emphasis is placed on this element, however the multi-elemental nature of PIXE is of course used. Several substrates have been investigated regarding minimum detection limits. Scanning Transmission Ion Macroscopy (STIM) analysis has been conducted on two outdoor aerosol samples, rendering three-dimensional images and mass distribution profiles. The setup was tested at ground level with high time resolution (5 min). Results show that the detection capabilities are excellent.
|
|
| 5. |
- Martinsson, Bengt G., et al.
(författare)
-
Fine mode particulate sulphur in the tropopause region measured from intercontinental flights (CARIBIC)
- 2001
-
Ingår i: Geophysical Research Letters. - 0094-8276. ; 28:7, s. 1175-1178
-
Tidskriftsartikel (refereegranskat)abstract
- Here the first systematic study of the concentration of particulate sulphur in the upper troposphere and lower stratosphere is presented. The measurements were undertaken in the CARIBIC programme during intercontinental flights from a commercial aircraft, which was equipped with an aerosol inlet and a research payload in the cargo bay. Aerosol samples were collected and analysed for elemental composition. The data set comprises 21 flights between Germany and Male/Colombo in the Indian Ocean. The average fine mode, particulate sulphur concentration was 14 ng/m3 STP, which is low compared to remote areas at the Earth's surface. A pronounced dependence with latitude with elevated concentrations occurring within the densely industrialised northern hemispheric mid latitudes was observed, thus suggesting anthropogenic influence on the climate from sulphate particles in the tropopause region.
|
|
| 6. |
- Martinsson, Bengt G., et al.
(författare)
-
Validation of very high cloud droplet number concentrations in air masses transported thousands of kilometres over the ocean
- 2000
-
Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - 0280-6509. ; 52:2, s. 801-814
-
Tidskriftsartikel (refereegranskat)abstract
- The microstructure of orographic clouds related to the aerosol present was studied during the second Aerosol Characterisation Experiment (ACE-2). Very high cloud droplet number concentrations (almost 3000 cm -3 ) were observed. These high concentrations occurred when clouds formed on a hill slope at Tenerife in polluted air masses originating in Europe that had transported the order of 1000 km over the Atlantic Ocean. The validity of the measured droplet number concentrations was investigated by comparing with measurements of the aerosol upstream of the cloud and cloud interstitial aerosol. Guided by distributions of the ratios between the measurements, three criteria of typically 30% in maximum deviation were applied to the measurements to test their validity. Agreement was found for 88% of the cases. The validated data set spans droplet number concentrations of 150-3000 cm -3 . The updraught velocity during the cloud formation was estimated to 2.2 m s -1 by model calculations, which is typical of cumuliform clouds. The results of the present study are discussed in relation to cloud droplet number concentrations previously reported in the literature. The importance of promoting the mechanistic understanding of the aerosol/cloud interaction and the use of validation procedures of cloud microphysical parameters is stressed in relation to the assessment of the indirect climatic effect of aerosols.
|
|
| 7. |
- Swietlicki, Erik, et al.
(författare)
-
Hygroscopic properties of aerosol particles in the northeastern Atlantic during ACE-2
- 2000
-
Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 52:2, s. 201-227
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the hygroscopic properties of sub-micrometer atmospheric aerosol particles were performed with hygroscopic tandem differential mobility analysers (H-TDMA) at 5 sites in the subtropical north-eastern Atlantic during the second Aerosol Characterization Experiment (ACE-2) from 16 June to 25 July 1997. Four of the sites were in the marine boundary layer and one was, at least occasionally, in the lower free troposphere. The hygroscopic diameter growth factors of individual aerosol particles in the dry particle diameter range 10-440 nm were generally measured for changes in relative humidity (RH) from <10% to 90%. In the marine boundary layer, growth factors at 90% RH were dependent on location, air mass type and particle size. The data was dominated by a unimodal growth distribution of more-hygroscopic particles, although a bimodal growth distribution including less-hygroscopic particles was observed at times, most often in the more polluted air masses. In clean marine air masses the more-hygroscopic growth factors ranged from about 1.6 to 1.8 with a consistent increase in growth factor with increasing particle size. There was also a tendency toward higher growth factors as sodium to sulphate molar ratio increased with increasing sea-salt contribution at higher wind speeds. During outbreaks of European pollution in the ACE-2 region, the growth factors of the largest particles were reduced, but only slightly. Growth factors at all sizes in both clean and polluted air masses were markedly lower at the Sagres, Portugal site due to more proximate continental influences. The frequency of occurrence of less-hygroscopic particles with a growth factor of ca. 1.15 was greatest during polluted conditions at Sagres. The free tropospheric 50 nm particles were predominately less-hygroscopic, with an intermediate growth factor of 1.4, but more-hygroscopic particles with growth factors of about 1.6 were also frequent. While these particles probably originate from within the marine boundary layer, the less-hygroscopic particles are probably more characteristic of lower free tropospheric air masses. For those occasions when measurements were made at 90% and an intermediate 60% or 70% RH, the growth factor G(RH) of the more-hygroscopic particles could be modelled empirically by a power law expression. For the ubiquitous more-hygroscopic particles, the expressions G(RH) = (1 - RH/100)-0.210 for 50 nm Aitken mode particles and G(RH) = (1 - RH/100)-0.233 for 166 nm accumulation mode particles are recommended for clean marine air masses in the north-eastern Atlantic within the range 0 < RH < 95%, and for wind speeds for which the local sea-salt production is small (< ca. 8 m s-1).
|
|
