A novel model to predict the physical state of atmospheric H2SO4/NH3/H2O aerosol particles

[摘要] The physical state of the tropospheric aerosol is largely unknowndespite its importance for cloud formation and for the aerosol's radiative properties. Here we use detailed microphysicallaboratory measurements to perform a systematic global modelling study of the physical state of theH₂SO₄/NH₃/H₂O aerosol, which constitutes animportant class of aerosols in the free troposphere. The Aerosol Physical State Model (APSM) developed here is based on Lagrangiantrajectories computed from ECMWF (European Centre for Medium Range Weather Forecasts) analyses, taking full account of thedeliquescence/efflorescence hysteresis. As input APSM requires three data sets: (i) deliquescence and efflorescence relativehumidities 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 liquidparticles increasing with altitude (between 2 and 10 km). In our calculations the most abundant solid isletovicite, (NH₄)₃H(SO₄)₂, while there is only littleammonium sulfate, (NH₄)₂SO₄. Since ammoniumbisulfate, NH₄HSO₄, does not nucleate homogeneously, itcan only form via heterogeneous crystallization. As the ammonia-to-sulfate ratios of the atmosphericH₂SO₄/NH₃/H₂O aerosol usually do notcorrespond to the stoichiometries of known crystalline substances, all solids are expected to occur in mixed-phase aerosol particles.This work highlights the potential importance of letovicite, whose role as cloud condensation nucleus (CCN) and as scatterer of solarradiation remains to be scrutinized.

[学科分类] 大气科学