PNNL

Abstract

Marine low clouds play an important role in the climate system, and their properties are sensitive to cloud condensation nuclei (CCN) concentrations. While new particle formation (NPF) represents a major source of CCN globally, the prevailing view is that NPF rarely occurs in remote marine boundary layer (MBL) over open oceans. Here we present evidences of the regular and frequent occurrence of NPF in the upper part of remote MBL following cold front passages. The NPF is facilitated by a combination of efficient removal of existing particles by precipitation, cold air temperatures, vertical transport of reactive gases from the ocean surface, and high actinic fluxes in a broken cloud field. The newly formed particles subsequently grow and contribute substantially to CCN in the remote MBL and thereby impact marine low clouds.