A novel model to predict the physical state of atmospheric H2SO4-NH3-H2O aerosol particlesReport as inadecuate

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1 IAC - Institute for Atmospheric and Climate Science Zürich

Abstract : The physical state of tropospheric aerosol particles is largely unknown despite its importance for cloud formation and for the aerosols- radiative properties. Here we show the first systematic global modelling study of the physical state of the H2SO4-NH3-H2O aerosol, which constitutes an important class of aerosols in the free troposphere. The Aerosol Physical State Model APSM developed here is based on Lagrangian trajectories computed from ECMWF European Centre for Medium Range Weather Forecasts analyses, taking full account of the deliquescence-efflorescence hysteresis. As input APSM requires three data sets: i deliquescence and efflorescence relative humidities from laboratory measurements, ii ammonia-to-sulfate ratios ASR calculated by a global circulation model, and iii relative humidities determined from the ECMWF analyses. APSM results indicate that globally averaged a significant fraction 17-57% of the ammoniated sulfate aerosol particles contain solids with the ratio of solid-containing to purely liquid particles increasing with altitude between 2 and 10 km. In our calculations the most abundant solid is letovicite, NH43HSO42, while there is only little ammonium sulfate, NH42SO4. Since ammonium bisulfate, NH4HSO4, does not nucleate homogeneously, it can only form via heterogeneous crystallization. As the ammonia-to-sulfate ratios of the atmospheric aerosol usually do not correspond to the stoichiometries of known crystalline substances, all solids are expected to occur in mixed-phase aerosol particles. This work highlights the global importance of letovicite, whose role as cloud condensation nucleus CCN and as scatterer of solar radiation remains to be scrutinized.

Author: C. A. Colberg - B. P. Luo - H. Wernli - T. Koop - Th. Peter -

Source: https://hal.archives-ouvertes.fr/


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