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RISS 인기검색어
- 검색키워드
- 저자 : Lelieveld, J. (검색결과 3 건)
- 무료
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- 유료
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Aerosol physicochemical effects on CCN activation simulated with the chemistry-climate model EMAC
Chang, D.Y.,Lelieveld, J.,Tost, H.,Steil, B.,Pozzer, A.,Yoon, J. Pergamon Press ; Elsevier [distribution] 2017 Atmospheric environment Vol.162 No.-
<P>This study uses the EMAC atmospheric chemistry-climate model to simulate cloud properties with a prognostic cloud droplet nucleation scheme. We present modeled global distributions of cloud condensation nuclei (CCN) number concentrations and CCN activation rates, together with the effective hygroscopicity parameter K, to describe the aerosol chemical composition effect on CCN activation. Large particles can easily activate into cloud droplets, even at low K values due to the dominant size effect in cloud droplet formation. Small particles are less efficiently activated as CCN, and are more sensitive to aerosol composition and supersaturation. Since the dominant fraction of small particles generally originates from anthropogenic precursor emissions over land, this study focuses on the influence of the continental atmosphere, using a prognostic cloud droplet nucleation scheme that considers aerosol cloud interactions during cloud formation, together with a double-moment cloud microphysics scheme. The agreement of simulated clouds and climate with observations generally improves over the Northern Hemisphere continents, particularly high air pollution regions such as Eastern US, Europe, East Asia by accounting for aerosol-cloud interactions that include impacts of chemical composition on CCN activation. (C) 2017 The Authors. Published by Elsevier Ltd.</P>
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Trend estimates of AERONET-observed and model-simulated AOTs between 1993 and 2013
Yoon, J.,Pozzer, A.,Chang, D.Y.,Lelieveld, J.,Kim, J.,Kim, M.,Lee, Y.G.,Koo, J.H.,Lee, J.,Moon, K.J. Pergamon Press ; Elsevier [distribution] 2016 Atmospheric environment Vol.125 No.1
<P>Recently, temporal changes in Aerosol Optical Thickness (AOT) have been investigated based on model simulations, satellite and ground-based observations. Most AOT trend studies used monthly or annual arithmetic means that discard details of the generally right-skewed AOT distributions. Potentially, such results can be biased by extreme values (including outliers). This study additionally uses percentiles (i.e., the lowest 5%, 25%, 50%, 75% and 95% of the monthly cumulative distributions fitted to Aerosol Robotic Network (AERONET)-observed and ECHAM/MESSy Atmospheric Chemistry (EMAC)-model simulated AOTs) that are less affected by outliers caused by measurement error, cloud contamination and occasional extreme aerosol events. Since the limited statistical representativeness of monthly percentiles and means can lead to bias, this study adopts the number of observations as a weighting factor, which improves the statistical robustness of trend estimates. By analyzing the aerosol composition of AERONET-observed and EMAC-simulated AOTs in selected regions of interest, we distinguish the dominant aerosol types and investigate the causes of regional AOT trends. The simulated and observed trends are generally consistent with a high correlation coefficient (R = 0.89) and small bias (slope +/- 2 sigma = 0.75 +/- 0.19). A significant decrease in EMAC-decomposed AOTs by water-soluble compounds and black carbon is found over the USA and the EU due to environmental regulation. In particular, a clear reversal in the AERONET AOT trend percentiles is found over the USA, probably related to the AOT diurnal cycle and the frequency of wildfires. In most of the selected regions of interest, EMAC-simulated trends are mainly attributed to the significant changes of the dominant aerosols; e.g., significant decrease in sea salt and water soluble compounds over Central America, increase in dust over Northern Africa and Middle East, and decrease in black carbon and organic carbon over Australia. (C) 2015 The Authors. Published by Elsevier Ltd.</P>
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