Marine Aerosol‐Cloud‐Climate Interaction

Abstract

Concerns over the role of atmospheric aerosols in masking observed climate change have sparked renewed interest in the natural emissions of trace gases (functioning as aerosol precursors) and aerosols. Understanding the aerosol budget in the absence of anthropogenic influence is necessary to establish a baseline aerosol forcing and provide a framework for models to properly interpret the historical climate record. Marine aerosol emissions, their composition, and their effects on clouds and radiation budget remain poorly characterized due to the large areal extent of the oceans and resulting scarcity of observational data. It is therefore not surprising that marine aerosols and associated cloud processes play a major role and present a large uncertainty, in predictions of future climate. This special issue was motivated by our perceived need to provide a platform for current discussions regarding marine aerosol-cloud-climate interactions. Much research had been performed in the 1950s–1970s following the discovery and initial characterization of the bubble burst process by Woodcock, Blanchard, McIntyre, Duce, and coworkers. A special issue appeared in the Journal of Geophysical Research in 1972 and research continued at a modest level over the next decades. Renewed interest in the subject appeared in the early 2000s, when a number of new studies identified large fractions of organic material in ambient marine aerosol in different locations, sparking an upsurge in laboratory, field, satellite, and modeling studies. These studies aimed to better characterize marine primary and secondary organic aerosol production mechanisms, aerosol mass and number fluxes, size-dependent sea spray enrichment factors, the split between water soluble and insoluble organic fractions, the chemical composition of organic aerosol, as well as to deter-mine the effect of marine organics on cloud microphysical properties. This special issue presents a snapshot of current research topics in this study area. It comprises twelve peer-reviewed open access articles spanning the full spectrum of atmospheric science research on this subject. A number of contributions address the chemical com-position of marine aerosols. Rinaldi et al. present a reviews and some innovative results on the chemical composition of primary and secondary marine aerosol, showing sea-sonal differences in nascent submicron sea spray particle chemical composition collected at the Mace Head Atmo-spheric Research Station. During low biological activity, submicron marine aerosols were primarily composed of sea salt, while particles collected during high biological activity largely contained nonsea salt sulfate and organics. Rinaldi et al. report distinct seasonal difference even in the organic composition of submicron marine aerosol. During low biological activity soluble and insoluble organic compounds were comparable in abundance, while during high biological activity submicron organics were dominated by water soluble organic matter. Hawkins and Russell use scanning Transmission X-ray Microscopy with Near-Edge X-ray Absorption Fine Structure (STXM-NEXAFS) analysis to classify marine primary organic aerosols collected in the Arctic and southeastern Pacific marine boundary layers into four major chemical types: carboxylic acid-containing