Abstract
Abstract. Lactic acid (LA) and glycolic acid (GA), which are low-molecular-weight hydroxyacids, were identified in the particle and gas phases within the marine atmospheric boundary layer over the western subarctic North Pacific. A major portion of LA (81%) and GA (57%) was present in the particulate phase, which is consistent with the presence of a hydroxyl group in these molecules leading to the low volatility of the compounds. The average concentration (±SD) of LA in more biologically influenced marine aerosols (33 ± 58 ng m−3) was substantially higher than that in less biologically influenced aerosols (11 ± 12 ng m−3). Over the oceanic region of phytoplankton blooms, the concentration of aerosol LA was comparable to that of oxalic acid, which was the most abundant diacid during the study period. A positive correlation was found between the LA concentrations in more biologically influenced aerosols and chlorophyll a in seawater (r2 = 0.56), suggesting an important production of aerosol LA possibly associated with microbial (e.g., lactobacillus) activity in seawater and/or aerosols. Our finding provides a new insight into the poorly quantified microbial sources of marine organic aerosols (OAs) because such low-molecular-weight hydroxyacids are key intermediates for OA formation.
Highlights
Ocean-derived organic aerosol (OA) is produced by wave breaking on sea surfaces and/or formed via atmospheric reactions
methanesulfonic acid (MSA) is known to be produced by the atmospheric oxidation of dimethylsulfide (DMS), which is released as a gas from marine microbial processes
Based on the concentrations of MSA and azelaic acid in aerosols sampled during the same cruise, Miyazaki et al (2010a) classified the aerosol samples into two categories: more biologically influenced aerosols (MBAs), composed of 17 samples obtained during 30 July–9 August, and less biologically influenced aerosols (LBAs), composed of 12 samples taken during 9–19 August
Summary
Ocean-derived organic aerosol (OA) is produced by wave breaking on sea surfaces and/or formed via atmospheric reactions. We report for the first time LA and GA in both the particle and gas phases in the ambient atmosphere over the western subarctic North Pacific in summer, where primary production rates are among the highest in the world oceans (Longhurst et al, 1995). We investigate their phase partitioning, possible sources, and the potential processes responsible for their presence in the marine aerosols. We discuss the importance of such low-molecularweight hydroxyacids as possible tracers of microbial activity in marine organic aerosols
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