Abstract
To better understand the impact of East Asian pollutants on the molecular composition of marine organic aerosols, we conducted long-term (2001–2013) observations of water-soluble dicarboxylic acids and related compounds in total suspended particulate samples collected at Chichijima Island in the western North Pacific (WNP). Seasonal variations of all the diacids and related compounds showed maxima in winter and spring and minima in summer, except for azelaic acid (C9), which maximized in summer to autumn. The overall annual concentrations of the total diacids, ω-oxoacids and α-dicarbonyls showed an increase during 2001–2013. We found a significant (p < 0.05) decadal increase in the inter-annual trends of pyruvic and glyoxylic (p > 0.05) acids, and methylglyoxal (MeGly). In contrast, phthalic acid (p < 0.05) and glyoxal (Gly) showed a decrease in their trends. We also found a significant decrease in the trend of the Gly/MeGly mass ratios. These results demonstrate that the enhanced concentrations of diacids over the WNP are majorly attributed to the aqueous-phase photooxidation of biogenic volatile organic compounds from East Asia followed by long-range atmospheric transport. Further, positive matrix factorization analysis showed a biogenic photochemical contribution (42%) was the dominant source of oxalic acid in the WNP.
Highlights
A large fraction of secondary organic aerosol (SOA) is derived from the oxidation of isoprene, monoterpenes and sesquiterpenes of biogenic origin
We carried out long-term (2001–2013) measurements of diacids and related compounds in total suspended particulate (TSP) aerosols collected at Chichijima Island in the western North Pacific (WNP)
Air mass transport from East Asia to the sampling site in the Pacific is stronger during winter (December to February) and spring (March to May) than during summer and autumn to deliver continental air masses via long-range atmospheric transport
Summary
A large fraction of secondary organic aerosol (SOA) is derived from the oxidation of isoprene, monoterpenes and sesquiterpenes of biogenic origin. Recent modelling studies[36] simulate an increased trend of isoprene emissions with 0.16% per year over Asia and this trend is more pronounced over China with 0.52% per year during 1979 to 2012. All these models, have significant uncertainties in the projection of SOA formation due to a series of fundamental assumptions and lack of long-term observational studies. The effects of East Asian pollutants and their outflows over the western North Pacific (WNP) are still unclear, especially with regard to the sources and formation of SOA during long-range transport[44,45,46]. We discuss the sources and formation pathways of the diacids using a positive matrix factorization (PMF) model
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