Abstract
In this study, spatiotemporal heterogeneities in the concentrations of alkaline gases and their particulate counterparts in the marine atmosphere over China's marginal seas were investigated in terms of causes and chemical conversion during two winter cruise campaigns, using semi-continuous measurements made by an onboard URG-9000D Ambient Ion Monitor-Ion chromatograph (AIM-IC, Thermofisher). During the cruise campaign over the East China Sea on December 27, 2019–January 6, 2020, the concentrations of atmospheric trimethylamine (TMAgas) varied by approximately one order of magnitude, with an average (±standard deviation) of 0.10 ± 0.04 µg m−3. Corresponding means were 0.037 ± 0.011 µg m−3 over the Yellow Sea on 7–16 January 2020 and 0.031 ± 0.009 μg m−3 over the Yellow Sea and the Bohai Sea on 9–22 December 2019. In contrast, the simultaneously observed concentrations of TMA in PM2.5, detected as TMAH+, over the East China Sea were 0.098 ± 0.068 µg m−3 and substantially smaller than 0.28 ± 0.18 μg m−3 over the Yellow Sea and the Bohai Sea on 9–22 December 2019. A significant correlation between TMAgas and particulate TMAH+ was obtained over the East China Sea, but no correlation existed over the Yellow Sea and Bohai Sea. The proportional or disproportional variations in concentrations of TMAgas with particulate TMAH+ over the sea zones were likely attributed to the difference in enrichment of TMAH+ in the sea surface microlayer. In addition, spatiotemporal heterogeneities in concentrations of atmospheric ammonia (NH3gas), atmospheric dimethylamine (DMAgas), and DMA in PM2.5, detected as DMAH+, were also investigated. Case analyses were performed to illustrate the formation and chemical conversion of particulate aminium ions in marine aerosols. Finally, we hypothesized a release of basic gases and particulate counterparts from the ocean to the atmosphere, together with secondary formation of DMAH+ and chemical conversion of TMAH+, in the marine atmosphere.
Highlights
In the marine atmosphere, gaseous ammonia (NH3gas) and amines, including trimethylamine (TMAgas) and dimethylamine (DMAgas), are unique alkaline gases that play an important role in neutralizing acids (Gibb et al, 1999; Johnson et al, 2007, 2008; Ge et al, 2011; Carpenter et al, 2012; Yu and Luo, 2014; Paulot et al, 2015; Wentworth et al, 2016; Chen et al, 2016; Köllner et al, 2017; van Pinxteren et al., 40 2019; Perraud et al, 2020)
We focused on investigating the spatiotemporal heterogeneity of the concentrations of NH3gas, TMAgas, and DMAgas, together with their particulate counterparts in marine atmospheres, by comparing observations during two winter cruise campaigns over the Yellow Sea, Bohai Sea, and the East China Sea
Combining the observational facts mentioned above, we argue that TMAH+ may be more highly enriched in the surface microlayer (SML) than in bulk surface seawater over the Yellow Sea and Bohai Sea, during Campaign A under the low surface seawater temperatures
Summary
Gaseous ammonia (NH3gas) and amines, including trimethylamine (TMAgas) and dimethylamine (DMAgas), are unique alkaline gases that play an important role in neutralizing acids (Gibb et al, 1999; Johnson et al, 2007, 2008; Ge et al, 2011; Carpenter et al, 2012; Yu and Luo, 2014; Paulot et al, 2015; Wentworth et al, 2016; Chen et al, 2016; Köllner et al, 2017; van Pinxteren et al., 40 2019; Perraud et al, 2020). The release of NH3gas from the ocean to the atmosphere is determined mainly by NH4+ concentrations in bulk seawater, surface seawater temperature, and pH of surface seawater (Johnson et al, 2007, 2008; Carpenter et al, 2012). In addition to the factors mentioned above, the release of TMAgas and DMAgas from the ocean to the atmosphere may be affected by the sea surface microlayer (SML), 45 because of the enrichment of TMA and DMA therein (van Pinxteren et al, 2019). TMA and DMA in bulk seawater theoretically undergo protonation as TMAH+ and DMAH+. It is unclear whether the amines enriched in the SML undergo protonation. The differences between inorganic and organic alkali causes different spatiotemporal variations in sea-derived emissions and concentrations of NH3gas from TMAgas and DMAgas, generating a large spatiotemporal heterogeneity in the molar ratios of
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