Abstract
Abstract. 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, Thermo Fisher). During the cruise campaign over the East China Sea from 27 December 2019 to 6 January 2020, the concentrations of gas-phase atmospheric trimethylamine (TMAgas) varied by approximately 1 order of magnitude, with an average (± standard deviation) of 0.10±0.04 µg m−3 corresponding to a mixing ratio of 26±17 pptv. Corresponding mean values were 0.037±0.011 µg m−3 (14±5 pptv in mixing ratio) over the Yellow Sea during the period from 7 to 16 January 2020 and 0.031±0.009 µg m−3 (12±4 pptv in mixing ratio) over the Yellow Sea and Bohai Sea from 9 to 22 December 2019. By contrast, the simultaneously observed concentrations of TMA in PM2.5, detected as TMAH+, over the East China Sea were 0.098±0.069 µg m−3 and substantially smaller than the 0.28±0.18 µg m−3 observed over the Yellow Sea and Bohai Sea from 9 to 22 December 2019. A significant correlation between TMAgas and particulate TMAH+ was observed over the East China Sea, but no correlation was found over the Yellow Sea and Bohai Sea. Proportional or disproportional variations in concentrations of TMAgas with particulate TMAH+ over the sea zones were probably attributed to the difference in the 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 investigated. Case analyses were performed to illustrate the formation and chemical conversion of particulate aminium ions in marine aerosols. Finally, we hypothesized the release of basic gases and particulate counterparts from the ocean to the atmosphere, together with the secondary formation of DMAH+ and chemical conversion of TMAH+, in the marine atmosphere.
Highlights
In a companion paper (Chen et al, 2021), we focused on identifying sea-derived alkaline gases and particulate counterparts in PM2.5 during a winter cruise campaign over the Yellow Sea and Bohai Sea, determined by an onboard URG9000D Ambient Ion Monitor-Ion Chromatograph (AIM-IC, Thermo Fisher)
We focused on investigating the spatiotemporal heterogeneity of 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 East China Sea
The average concentration of TMAH+ in PM2.5 over the East China Sea was 0.098 ± 0.068 μg m−3, and the average increased by approximately 200 % to 0.28 ± 0.18 μg m−3 over the Yellow Sea and Bohai Sea in Campaign A
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, 2019; Perraud et al, 2020). TMA and DMA may further biochemically decompose into small molecules (Hu et al, 2015, 2018; Lidbury et al, 2014, 2015; Xie et al, 2018) These two factors would alter the ratios of TMAgas (DMAgas) to NH3gas in oceanic emissions in opposite directions. We focused on investigating the spatiotemporal heterogeneity of 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 East China Sea. previously reported episodic concentrations of particulate TMAH+ and DMAH+ observed in the marine atmosphere over the Yellow Sea were included to deepen the understanding of size distributions of aminium ions, the ratio of aminium ions to NH+4 , and related primary or secondary origins of particulate aminium ions. Building on the analysis results, a hypothesis is presented to illustrate the release of gaseous alkali and their counterparts from the ocean to the atmosphere and related chemical conversions in the marine atmosphere
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