Chemical Characterization of Isoprene- and Monoterpene-Derived Secondary Organic Aerosol Tracers in Remote Marine Aerosols over a Quarter Century

Isoprene and monoterpenes are ubiquitous precursors of biogenic secondary organic aerosol (SOA) over continental regions; however, their contributions to organic aerosol (OA) mass and chemical processes in remote marine atmospheres remain uncertain. Determining exact sources of organics in marine aerosol is needed to more accurately assess aerosol climate effects in remote locations through coupled atmospheric chemistry–climate simulations. Over 200 archived ocean-originated particulate samples collected from 1991 to 2015 at Cape Grim, Australia, were analyzed using a suite of chromatographic and mass spectrometric techniques. To our knowledge, this is one of the longest running continual archives of marine aerosol samples collected under remote background conditions. Up to 6.75 and 1.11 ng m–3 of isoprene- and monoterpene-derived SOA, respectively, were quantified using authentic standards. Although there was no clear temporal trend over the decades, consistent seasonal variations were observed, with higher biogenic SOA in summer, which was moderately to strongly correlated (r = 0.61–0.85) with marine bioactivity indicators, such as methanesulfonic acid and chlorophyll a. These correlations indicate that marine biota likely emit biogenic SOA precursors that are able to contribute to remote background OA levels. On the basis of historical observations of OA mass estimated in the marine baseline samples, these biogenic SOA tracers contributed up to 0.71% (0.26 ± 0.24% on average) of the total OA mass fraction. Our data suggest that larger sources of OA exist in remote marine atmospheres, such as primary OA produced from bubble-bursting processes or SOA precursors derived from photosensitized reactions of dissolved organic matter present in the sea surface microlayer.