Abstract
Abstract. Samples of fog water were collected at Baengnyeong Island (BYI) in the Yellow Sea during the summer of 2014. The most abundant chemical species in the fog water were NH4+ (mean of 2220 µM), NO3− (1260 µM), SO4−2 (730 µM), and Na+ (551 µM), with substantial contributions from other species consistent with marine and biomass burning influence on some dates. The pH of the samples ranged between 3.48 and 5.00, with a mean of 3.94, intermediate within pH values of fog/cloud water reported previously in Southeast Asia. Back trajectories (72 h) showed that high relative humidity ( > 80 %) was encountered upwind of the sampling site by all but one of the sampled air masses, and that the fog composition at BYI can be impacted by several different source regions, including the Sea of Japan, southeastern China, northeastern China, and the East China Sea. Sulfur in the collected fog was highly oxidized: low S(IV) concentrations were measured (mean of 2.36 µM) in contrast to SO4−2 and in contrast to fog/cloud S(IV) concentrations from pollutant source regions; organosulfate species were also observed and were most likely formed through aging of mainly biogenic volatile organic compounds. Low-molecular-mass organic acids were major contributors to total organic carbon (TOC; 36–69 %), comprising a fraction of TOC at the upper end of that seen in fogs and clouds in other polluted environments. Large contributions were observed from not only acetic and formic acids but also oxalic, succinic, maleic, and other organic acids that can be produced in aqueous atmospheric organic processing (AAOP) reactions. These samples of East Asian fog water containing highly oxidized components represent fog downwind of pollutant sources and can provide new insight into the fate of regional emissions. In particular, these samples demonstrate the result of extensive photochemical aging during multiday transport, including oxidation within wet aerosols and fogs.
Highlights
The chemistry of the atmosphere occurs within multiple phases, one of which is the aqueous phase
Fog water was collected during nine fog events (17 total samples) at the Baengnyeong Island (BYI) atmospheric research center (ARC) during July 2014; seven events and 13 samples were included in mean chemical concentrations calculated over the duration of the sampling campaign and will be discussed here (Fig. 1)
Major inorganic species contributing to the measured acidity of the fog water at BYI (Table 1; Fig. 3) were NH+4, followed by
Summary
The chemistry of the atmosphere occurs within multiple phases, one of which is the aqueous phase. Atmospheric water includes fog droplets, cloud droplets, and wet aerosol particles, all of which can act as miniature aqueous reaction vessels. Distinct chemical phenomena occur within the atmospheric aqueous phase: formation of organic hydrates and protonation/deprotonation occur frequently, time spent by reactants in proximity to one another increases, and interactions involving metals such as the Fenton reactions and iron oxalate complexes are possible (Lelieveld and Crutzen, 1991; Zuo and Hoigné, 1994). The study of carbonaceous species is pertinent to understanding particle-, gas-, and aqueous-phase atmospheric processes because the composition and formation of organics are complex.
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