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| 2. |
- Bower, K. N., et al.
(författare)
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ACE-2 HILLCLOUD. An overview of the ACE-2 ground-based cloud experiment
- 2000
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 52:2, s. 750-778
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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.
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| 3. |
- Mentes, B., et al.
(författare)
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Ion-beam thermography analysis of the H2SO4-(NH4)2SO4 system in aerosol samples
- 2000
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 168:4, s. 533-542
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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.
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| 5. |
- Martinsson, B. G., et al.
(författare)
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Methodology to estimate the transfer function of individual differential mobility analyzers
- 2001
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 35:4, s. 815-823
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Tidskriftsartikel (refereegranskat)abstract
- A method to estimate the nonideal features of the transfer function of individual differential mobility analyzers (DMA) was developed and tested experimentally. This was up to now an unsolved problem, which is important for the precision in DMA measurements. The method involves three DMAs of unknown characteristics, which are used in three rounds of experiments with two DMAs according to a fixed schedule. The width of the transfer functions of the three DMAs is obtained in a single fitting procedure where one parameter is fitted to each DMA transfer function and the particle losses in each DMA are calculated in direct relation to that parameter and parameters known from the experiment. It was shown that the proposed method could solve the apportioning problem and unambiguously estimate the transfer function width and the particle losses in each of the DMAs.
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