Abstract
Abstract. An integrated observation of aerosol aminiums was conducted in a coastal city (Shanghai) in eastern China, a nearby island (Huaniao Island), and over the Yellow Sea and East China Sea (YECS). Triethylaminium (TEAH+) was abundant over Shanghai but not detected over the island and the open seas, suggesting its predominantly terrestrial origin. By contrast, relatively high concentrations of dimethylaminium (DMAH+) and trimethylaminium + diethylaminium (TMDEAH+) were measured over the ocean sites, indicating the significant marine source contribution. Environmental factors, including boundary layer height (BLH), temperature, atmospheric oxidizing capacity and relative humidity, were found to be related to aminium concentrations. All the detected aminiums demonstrated the highest levels in winter in Shanghai, consistent with the lowest BLH and temperature in this season. Aminiums mainly existed in fine particles and showed a bimodal distribution, with two peaks at 0.18–0.32 µm and 0.56–1.0 µm, indicating that condensation and cloud processing were the main formation pathways for aminiums in analogy with NH4+ and non-sea-salt SO42- (nss-SO42-). Nonetheless, a unimodal distribution for aerosol aminiums was usually measured over the YECS or over Huaniao Island when influenced mainly by the marine air mass, which suggested that aminiums in marine aerosols may undergo different formation pathways from those on the land. Terrestrial anthropogenic sources and marine biogenic sources were both important contributors for DMAH+ and TMDEAH+, and the latter exhibited a significantly higher TMDEAH+ to DMAH+ ratio. By using the mass ratio of methanesulfonate (MSA) to nss-SO42- as an indicator of marine biogenic source, we estimated that marine biogenic source contributed to 26 %–31 % and 53 %–78 % of aerosol aminiums over Huaniao Island in the autumn of 2016 and summer of 2017, respectively. Due to the important role of atmospheric amines in new particle formation, the estimation results highlighted the importance of marine biogenic emission of amines on the eastern coast of China, especially in summer.
Highlights
Low molecular weight amines are commonly found in the atmosphere in both gas and particle phases (Ge et al, 2011a, b)
DMAH+, TMDEAH+ and TEAH+, were commonly detected in the aerosol samples collected from Shanghai
All three aminiums showed the highest concentrations in winter and the lowest levels in spring (DMAH+) and summer (TMDEAH+ and TEAH+), which generally agreed with the seasonal trends of PM2.5 and NH+4 concentrations in Shanghai (Fig. 2)
Summary
Low molecular weight amines are commonly found in the atmosphere in both gas and particle phases (Ge et al, 2011a, b). In May 2012, the concentrations of DMAH+ and TMAH+ over the Yellow Sea (YS) and Bohai Sea even reached 4.4 and 7.2 nmol m−3, which was 1–3 orders of magnitude higher than those reported in other oceanic regions (Hu et al, 2015) These extremely high concentrations were thought to be associated with high biological activities. In spite of these field studies, long-term observations of aminiums over coastal seas and the quantitative estimates of the contribution of marine biogenic source to aerosol aminiums are still lacking. Our results will be a great help for understanding the chemical properties, reaction pathways, and sources of aerosol aminiums over the coastal area and the ocean
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