CAM: A Size Segregated Simulation of Atmospheric Aerosol Processes for Climate and Air Quality Models J. Geophy. Res. 2002 (in press)1.Module Development

S.L. Gong1, L.A. Barrie2, J.-P. Blanchet3, K. von Salzen5, U. Lohmann4, G. Lesins4, L. Spacek3, L.M. Zhang1, E. Girard3, H. Lin1, R. Leaitch1, H. Leighton5, P. Chylek4 and P. Huang12. Global sea-salt aerosol and its budgetsS.L. Gong1, L.A. Barrie2 and M. Lazare1

Model Configurations CAM/GCM

Aerosols

12 bin sectional model: r=0.005 20.48 m [dry]

Sources

GEIA 1B: 2-level anthropogenic SO2 and SO4

Kettle et al. : Surface DMS concentration

Benkovitz et al. : H2S monthly mean flux

Gong et al. : Sea-salt surface flux

Prognostic

Variables

Sea-salt and sulphate mass mixing ratio in each size bin, cloud water and ice, DMS, SO2, H2S and H2SO4[g]

Clear-sky

processes

Nucleation, condensation, coagulation, on-line S chemistry with MOZARTs OH and NO3

Wet

Processes

Gong et al : Below-cloud scavenging

Lohmann : Explicit cloud scheme

Cloud activation and cloud S chemistry with MOZARTs O3, H2O2 and HNO3, and NH3

Dry Deposition

Size-dependent particle and SO2

Resolution

96(48(22, 20 min

Global Sea-salt Simulations and Budgets

Global Sea-salt Concentrations

Global Sea-salt Compared with ObservationsComparison Sites [WCRP/IGAC COSAM]

Sea-salt Size Distributions(d) Model 197 hPa(b) Quinn et al. [1996] Surface(c) Model 698 hPa(a) Model 995 hPaCompare

Global Sea-salt Residence Times - Coarse

Global Sea-salt Residence Times - Fine

Annual Global Sea-salt Budgets 1012 kggiga-ton

Global Monthly Sea-salt Emissions

Global Sulphate Aerosols Influenced by Sea-salt

Global Sulphate Concentrations

Global Sulphate Compared with ObservationsComparison Sites [WCRP/IGAC COSAM]

Volume Size DistributionsQuinn et al. 1996Simulations140W, 40S

Global Sulphate Distributions

Surface Reduction of Sulphate by Sea-salt-20~30%-50~70%-20~30%Rosenfeld et al 2002, ScienceSea-salt cleans air pollution-10~20%

Mechanisms of the Sea-salt Impact (1)Cleaning AgentsCondensation of sulphuric acid vapour onto existing sea-salt particles reduces the atmospheric sulphate cycling time and hence reduces the sulphate concentrations.Sea-salt aerosols override the precipitation suppression effects of the large number of small pollution nuclei.

Impact of Sea-salt on Sulphate Number Size Distributions Sea-salt reduces the number concentration of sulphate by enhancing condensation and coagulations.

Mass-mean Diameters of Sulphate (MAM)Increases in MMD reduce the residence time and hence concentrations of sulphate.

Mechanisms of the Sea-salt Impact (2)Effects on CloudsSea-salt provides additional CCN for SO2 in-cloud oxidation and hence increases the sulphate concentrations.An increase more than 20% in in-cloud sulphate production due to additional sea-salt particles and higher pH associated with newly formed sea-salt-nucleated cloud droplets compared to sulphate. [ODowd et al. 1997, Lowe et al. 1995]

Sea-salt on cloud droplet number[Pszenny et al 1998][ODowd et al. 1999][Rosenfeld et al 2002]Sea-salt aerosols override the precipitation suppression effects of the large number of small pollution nuclei.

The enhancement in precipitation helps remove pollution.

Changes of Sulphate MMR by Sea-salt10~20%Competitive processes of sea-salt with positive and negative effects on sulphate.

Location dependent.

ConclusionsThe global annual sea-salt emission to the atmosphere is about 1.011013 kg with 68% in the southern hemisphere.

Residence times of 7.7 mm and 0.4 mm diameter sea salt particles in the marine boundary layer were in the range 0.3 - 10 hours and 80 360 hours, respectively.

By serving as a quenching agent to nucleation and additional surface area for condensation, sea-salt aerosols increase the mass mean diameter of sulphate aerosols by a factor of 2 and reduce the global sulphate aerosol mass in the surface MBL layer from 5 to 75% for most of the open oceans.