The microphysical and radiative properties of marine stratocumulus clouds are very susceptible to the changes in availability of marine aerosol, rendering it one of the most important aspects in the global climate system. However, the knowledge of marine aerosol and its climatic impact are poorly constrained in global models. Marine aerosol can be generally divided into sea spray aerosol and secondary marine aerosol. The former is produced via wind-sea surface interaction and the later is formed via gas-to-particle formation. The inability to distinguish sea spray aerosol and secondary marine aerosol has greatly hindered our ability to accurately predict marine radiative balance.

In this study, we developed a unique and novel approach to identify sub-micron sea spray aerosol by using size-resolved hygroscopicity measurement based on tandem humidified differential mobility analyzer. We found that the number concentrations of sub-micron sea spray aerosol have been greatly underestimated by traditional estimates, which utilizes a super-board lognormal distribution fitting.

Based on the combination of field measurement and lab experiments, we also found that heterogenous iodine-organic chemistry leads to the acceleration of nanoparticle growth. This new mechanism can explain the fast growth of marine new particle in the marine boundary layer.

Last, by combining cloud condensation nuclei (CCN) measurements, we evaluate the impact of mixing state and size-resolved hygroscopicity in estimating the CCN number. We found that neglect of mixing state and size-resolved hygrosocpicity leads to over-estimation of CCN. A better appreciation of marine aerosol is likely to improve our understanding towards cloud formation in marine air and thus the global climate.

References:

Xu, W., Ovadnevaite, J., Fossum, K. N., Lin, C., Huang, R.-J., Ceburnis, D., and O’Dowd, C.: Nat Geosci, 15, 282–286, 2022.

Huang, R.-J., Hoffmann, T., Ovadnevaite, J., Laaksonen, A., Kokkola, H., Xu, W., Xu, W., Ceburnis, D., Zhang, R., Seinfeld, J. H., and O’Dowd, C.: Proc National Acad Sci, 119, e2201729119, 2022.

Xu, W., Fossum, K. N., Ovadnevaite, J., Lin, C., Huang, R.-J., O’Dowd, C., and Ceburnis, D.: Atmos Chem Phys, 21, 8655–8675, 2021.