Abstract
Abstract. Knowledge of the physical characteristics and chemical composition of marine organic aerosols is needed for the quantification of their effects on solar radiation transfer and cloud processes. This review examines research pertinent to the chemical composition, size distribution, mixing state, emission mechanism, photochemical oxidation and climatic impact of marine primary organic aerosol (POA) associated with sea-spray. Numerous measurements have shown that both the ambient mass concentration of marine POA and size-resolved organic mass fraction of sea-spray aerosol are related to surface ocean biological activity. Recent studies have also indicated that fine mode (smaller than 200 nm in diameter) marine POA can have a size distribution independent from sea-salt, while coarse mode aerosols (larger than 1000 nm in diameter) are more likely to be internally mixed with sea-salt. Modelling studies have estimated global submicron marine POA emission rates of ~10 ± 5 Tg yr−1, with a considerable fraction of these emissions occurring over regions most susceptible to aerosol perturbations. Climate studies have found that marine POA can cause large local increases in the cloud condensation nuclei concentration and have a non-negligible influence on model assessments of the anthropogenic aerosol forcing of climate. Despite these signs of climate-relevance, the source strength, chemical composition, mixing state, hygroscopicity, cloud droplet activation potential, atmospheric aging and removal of marine POA remain poorly quantified. Additional laboratory, field, and modelling studies focused on the chemistry, size distribution and mixing state of marine POA are needed to better understand and quantify their importance.
Highlights
OcDflimnaaattatueramSl oyadeserotlsesosmtlrso,snthgelyreinpflreuseenncteashave indicated that fine mode marine primary organic aerosol (POA) can have a size distribution indepen- thropogenic aerosols
Past studies show that the average bulk concentration of marine POA and organic/sea-salt ratio in clean marine environments is 0.4 ± 0.3 μg m−3 and 0.1, respectively, with spatiotemporal differences related to surface wind speed and ocean physical and biological state that may result in concentrations and organic/seasalt ratios that are nearly an order of magnitude higher or lower
Measurements indicate that the rate of photochemical aging of marine POA during the atmospheric transport is likely controlled by the seawater chemical/biological composition: freshly produced low molecular weight (LMW) organic compounds can be readily degraded by photochemistry while refractory forms of dissolved organic matter may strongly resist photodegradation (Mopper et al, 1991)
Summary
The first detectors of organic matter in SSA used surface active nature of organics to separate them from sea-salt (Blanchard, 1964). Barger and Garrett (1970) collected SSA from the Hawaiian coast on glass fiber filters and determined the concentration of chloroform extractable surface-active organic matter to be 0.7 to 7.9 μg m−3, contributing 5 to 15 % of airborne particulate mass. Past studies show that the average bulk concentration of marine POA and organic/sea-salt ratio in clean marine environments is 0.4 ± 0.3 μg m−3 (mean and standard deviation from Table S1) and 0.1, respectively, with spatiotemporal differences related to surface wind speed and ocean physical and biological state that may result in concentrations and organic/seasalt ratios that are nearly an order of magnitude higher or lower
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