CMAQv5.1 Sea Spray Aerosol Update

Brief Description

Sea spray aerosols (SSAs) impact the particle mass concentration and gas-particle partitioning in coastal environments, with implications for human and ecosystem health. Model evaluations of SSA emissions have mainly focused on the global scale, but regional-scale evaluations are also important due to the localized impact of SSAs on atmospheric chemistry near the coast. In CMAQ v5.1, SSA emissions were updated to enhance the fine-mode size distribution, include sea surface temperature (SST) dependency, and reduce surf-enhanced emissions.

Updates to Sea Salt Aerosol Emissions

• Updated the size distribution of sea salt aerosol of Gong (2003) to better reflect fine scale aerosol measurements in laboratory and field based studies (de Leeuw et al. 2011).
• Added a sea surface temperature dependency on water viscosity and its impact on sea salt aerosol emissions (Gantt et al. 2015).
• Reduced the surf zone emissions to address a systematic overestimate of near shore coarse sea salt aerosol concentrations (Gantt et al. 2015).

Significance and Impact

These changes were tested for spring and summertime simulations for 2002 and 2010 on the Conterminous 12 kilometer US domain. These sea salt aerosol emission updates led to increases in the fine-mode sodium surface concentrations throughout coastal areas of the continental US, with the largest increases occurring near the southeastern US coast where sea surface temperatures (SSTs) were high. Decreases in the total sodium concentration were predicted for oceanic regions with relatively low SSTs such as the Pacific and northern Atlantic coasts. Comparison of the baseline and revised simulation with sodium observations from the IMPROVE and CSN networks showed that the updated emissions reduced the widespread underprediction of concentrations, especially in the southeastern and mid-Atlantic US. Non-linear responses between changes in total and sea salt PM_2.5 concentrations indicated that the impacts of these emissions changes on aerosol chemistry were enhanced in polluted coastal environments. The change in SSA algorithms had increased sodium and nitrate aerosol concentrations at most CalNex sites, slightly reducing the underprediction from the baseline simulation (Gantt et al., 2015).

Affected Files

SSEMIS.F

References

Gantt, B., Kelly, J.T., Bash, J.O., Updating sea spray aerosol emissions in the Community Multiscale Air Quality (CMAQ) model version 5.0.2, Geosci. Model Dev., 8, 3733-3746, doi:10.5194/gmd-8-3733-2015, 2015

Gong, S. L.: A parameterization of sea-salt aerosol source function for sub- and super-micron particles, Global Biogeochem. Cy., 17, 1097, doi:10.1029/2003gb002079, 2003.

de Leeuw, G., Andreas, E. L., Anguelova, M. D., Fairall, C. W., Lewis, E. R., O’Dowd, C., Schulz, M., and Schwartz, S. E.: Production flux of sea spray aerosol, Rev. Geophys., 49, RG2001, doi:10.1029/2010RG000349, 2011.

Contact

Jesse Bash, National Exposure Research Laboratory, U.S. EPA, Brett Gantt, Office of Air Quality Planning and Standards, U.S. EPA