Concentration, Size Distribution, and Formation of Trimethylaminium and Dimethylaminium Ions in Atmospheric Particles over Marginal Seas of China

Abstract

n this paper, the concentration, the size distribution, and the formation of dimethylaminium (DMA+) and trimethylaminium (TMA+) ions in atmospheric particles were studied during a cruise campaign over the Yellow Sea and the Bohai Sea of China in May 2012. The concentrations of DMA+ and TMA+ in particles smaller than 11 µm were 4.4 ± 3.7 and 7.2 ± 7.1 nmol m?3, respectively. The two ions had a good correlation (R2 = 0.86), and both had a moderately good correlation with chlorophyll a fluorescence (R2 = 0.66?0.67). The observed concentrations were from one to three orders of magnitude larger than the concentrations reported in other marine atmospheres. They were also much larger than the values observed at a coastal site neighboring the Yellow Sea in May?June 2013. The high concentrations of DMA+ and TMA+ observed in the marine atmosphere were probably associated with local biogenic activity instead of the long-range transport of these species from adjacent continents. The calculated mole ratios of (DMA+ + TMA+) to in different-sized particles over the seas indicated that (DMA+ + TMA+) most likely played an important role in neutralizing acidic species in particles less than 0.43 µm but not in particles of other sizes. Size distributions of DMA+ and TMA+ in the marine and coastal atmospheres were analyzed in terms of the respective contribution of gas?particle partitioning, cloud/fog processing of TMA+ and DMA+, bioaerosols, and sea-salt aerosols to the observed concentrations of the two ions over the seas.