A global off-line model of size-resolved aerosol microphysics: II. Identification of key uncertainties

[摘要] We use the new GLOMAP model of global aerosol microphysics toinvestigate the sensitivity of modelled sulfate and sea salt aerosolproperties to uncertainties in the driving microphysical processes andcompare these uncertainties with those associated with aerosol andprecursor gas emissions. Overall, we conclude that uncertainties inmicrophysical processes have a larger effect on global sulfate and seasalt derived condensation nuclei (CN) and cloud condensation nuclei(CCN) concentrations than uncertainties in present-day sulfuremissions. Our simulations suggest that uncertainties in predictedsulfate and sea salt CCN abundances due to poorly constrainedmicrophysical processes are likely to be of a similar magnitude tolong-term changes in sulfate and sea salt CCN due to changes inanthropogenic emissions. A microphysical treatment of the globalsulfate aerosol allows the uncertainty in climate-relevant aerosolproperties to be attributed to specific processes in a way that hasnot been possible with simpler aerosol schemes. In particular weconclude that: (1) changes in the binary H₂SO₄-H₂Onucleation rate and condensation rate of gaseous H₂SO₄ causea shift in the vertical location of the upper tropospheric CN layer byas much as 3 km, while the shape of the CN profile isessentially pre-served (2) uncertainties in the binaryH₂SO₄-H₂O nucleation rate have a relatively insignificanteffect on marine boundary layer (MBL) aerosol properties; (3) emitting afraction of anthropogenic SO₂ as particulates (to representproduction of sulfate particles in power plant plumes below the scaleof the model grid (which is of the order of 300 km)) has thepotential to change the global mean MBL sulfate-derived CN concentrationsby up to 72%, and changes of up to a factor 20can occur in polluted continental regions; (4) predicted global meanMBL sulfate andsea salt CCN concentrations change by 10 to 60% whenseveral microphysical processes are changed within reasonableuncertainty ranges; (5) sulfate and sea salt derived CCNconcentrations are particularly sensitive to primary particleemissions, with global mean MBL sulfate and sea salt CCN changing by up to27% and local concentrations over continental regions changing by more than 100% when thepercentage of anthropogenicSO₂ emitted as particulates is changed from 0 to5%; (6) large changes in sea spray flux have insignificant effects onglobal sulfate aerosol except when the mass accommodation coefficientof sulfuric acid on the salt particles is set unrealistically low.

[学科分类] 大气科学