Abstract
Abstract. The sources and seasonal trends of water-soluble organic carbon (WSOC) in carbonaceous aerosols are of significant interest. From July 2017 to July 2019, we collected samples of PM2.5 (particulate matter, aerodynamic diameter<2.5 µm) from one suburban and one rural site in Japan. The average δ13CWSOC was -25.2±1.1 ‰ and -24.6±2.4 ‰ at the suburban site and rural site, respectively. At the suburban site, the δ13CWSOC was consistent with the δ13C of burned C3 plants, and a high correlation was found between WSOC concentrations and non-sea-salt potassium concentrations; these results suggest that the main source of WSOC at this site was biomass burning of rice straw. At the rural site, the average δ13CWSOC was significantly heavier from autumn to spring (-23.9±2.1 ‰) than in summer (-27.4±0.7 ‰) (p<0.01). The δ13CWSOC from autumn to spring was consistent with that of biomass burning of rice straw, whereas that in summer was considered to reflect mainly the formation of secondary organic aerosols from biogenic volatile organic compounds (VOCs). The heaviest δ13CWSOC (-21.3±1.9 ‰) was observed from February to April 2019, which may be explained by long-range transport of C4 plant burning such as corn from overseas. Thus, the present study indicates that δ13CWSOC is potentially useful for elucidating the sources and atmospheric processes that contribute to seasonal variations of WSOC concentration.
Highlights
Particulate matter (PM) has deleterious effects on human health and contributes to climate change (Pope et al, 1995; Lohmann and Feichter, 2005)
The mass concentrations of PM2.5 were consistent with the seasonal variation for nearby sites of the Atmospheric Environmental Regional Observation System (AEROS) provided by the Ministry of the Environment (Ministry of the Environment, 2021)
The strong correlation that was found between the annual-average water-soluble organic carbon (WSOC) concentration and annual-average elemental carbon (EC) concentration (r = 0.71) suggests that the WSOC at this suburban site is from combustion sources
Summary
Particulate matter (PM) has deleterious effects on human health and contributes to climate change (Pope et al, 1995; Lohmann and Feichter, 2005). This newer approach is highly sensitive, so only small amounts of sample are needed compared to the combustion method Despite these improved approaches and the significant interest in the seasonal trends and source apportionment of WSOC, no studies have examined the change of δ13CWSOC in PM2.5 over a long period of time to understand seasonal variability. We characterized the source of WSOC and any atmospheric processes it had undergone using isotope-based approaches We believe that this is the first report of the use of the wet-oxidation–IRMS method (Suto and Kawashima, 2018) for long-term observation of δ13CWSOC
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