Modeling and evaluation of the global sea-salt aerosol distribution: Sensitivity to emission schemes and resolution effects at coastal/orographic sites
One of the major sources of uncertainty in model estimates of the global sea-salt aerosol distribution is the emission parameterization. We evaluate a new sea-salt aerosol life cycle module coupled to the online multiscale chemical transport model NMMB/BSC-CTM. We compare 5 yr global simulations using five state-of-the-art sea-salt open-ocean emission schemes with monthly averaged coarse aerosol optical depth (AOD) from selected AERONET sun photometers, surface concentration measurements from the University of Miami’s Ocean Aerosol Network, and mea- surements from two NOAA/PMEL cruises (AEROINDOEX and ACE1). Model results are highly sensitive to the intro- duction of sea-surface-temperature (SST)-dependent emis- sions and to the accounting of spume particles production. Emission ranges from 3888 Tg yr−1 to 8114 Tg yr−1 , life- time varies between 7.3 h and 11.3 h, and the average col- umn mass load is between 5.0 Tg and 7.2 Tg. Coarse AOD is reproduced with an overall correlation of around 0.5 and with normalized biases ranging from +8.8 % to +38.8 %. Surface concentration is simulated with normalized biases ranging from −9.5 % to +28 % and the overall correlation is around 0.5. Our results indicate that SST-dependent emission schemes improve the overall model performance in repro- ducing surface concentrations. On the other hand, they lead to an overestimation of the coarse AOD at tropical latitudes, although it may be affected by uncertainties in the compar- ison due to the use of all-sky model AOD, the treatment of water uptake, deposition and optical properties in the model and/or an inaccurate size distribution at emission.