A simple non-linear analytical relationship between aerosol accumulation number and sub-micron volume, explaining their observed ratio in the clean and polluted marine boundary layer

We propose an analytical expression for the relation between aerosol accumu lation number and sub-micron volume over the marine boundary layer (MBL), b ased on a simple balance equation. By providing appropriate source and sink terms which account for entrainment, coagulation, in-cloud scavenging and condensational growth, the model is able to reproduce the observed ratio be tween MBL particles larger than 80 nm diameter (as a proxy for accumulation mode number) and submicron aerosol volume, from freshly polluted to backgr ound conditions. Entrainment and coagulation are essential in predicting th e observed ratio. Budget and lifetime calculations show that, due to relati vely low source rates of oceanic non-sea-salt-sulfate and sea-salt, the ant hropogenic signature in aerosol volume remains significant even after 8 day s of MBL transport.