Marine boundary-layer aerosol in Eastern North Atlantic: seasonal variations and key processes

 

Submitter:

Wang, Jian - Washington University in St. Louis

Area of research:

Cloud-Aerosol-Precipitation Interactions

Journal Reference:

Zheng G, Y Wang, A Aiken, F Gallo, M Jensen, P Kollias, C Kuang, E Luke, S Springston, J Uin, R Wood, and J Wang. 2018. "Marine boundary layer aerosol in the eastern North Atlantic: seasonal variations and key controlling processes." Atmospheric Chemistry and Physics, 18(23), doi:10.5194/acp-18-17615-2018.

Science

Here we elucidate the key processes that drive marine boundary-layer (MBL) aerosol size distribution in the Eastern North Atlantic (ENA) using long-term measurements. The governing equations of particle concentration are established for different modes.

Impact

Our results show that particles entrained from the free troposphere represent the major source of MBL cloud condensation nuclei (CCN), contributing both directly to the CCN population and indirectly by supplying small particles that grow to CCN in the MBL. The importance of growth of small particles suggests a substantial influence of ocean ecosystems on MBL CCN in ENA.

Summary

The response of marine low clouds to changes in aerosol concentration represents one of the largest uncertainties in climate simulations. Major contributions to this uncertainty derive from poor understanding of aerosol under natural conditions and the perturbation by anthropogenic emissions. Here we investigated this issue through long-term (2015-2017) measurements at the Atmospheric Radiation Measurement Eastern North Atlantic site, a region of persistent marine boundary-layer (MBL) clouds. We first proposed the mode-dependent governing equations of aerosol number budgets, the applicability of which are verified by observations. Based on the governing equations, quantification analysis are conducted to reveal the key processes that drive MBL aerosol size distributions. The results show that particles entrained from the free troposphere represent the major source of MBL cloud condensation nuclei (CCN), contributing both directly to CCN population and indirectly by supplying Aitke- mode particles that grow to CCN in the MBL. The indirect contribution may dominate during summer and fall seasons. As the growth of Aitken-mode particles to CCN size is an expected result of the condensation of sulfuric acid, a product from dimethyl sulfide oxidation, this study suggests ocean ecosystems may have a substantial influence on MBL CCN populations in ENA.