Large Increases in Primary Trimethylaminium and Secondary Dimethylaminium in Atmospheric Particles Associated With Cyclonic Eddies in the Northwest Pacific Ocean

Abstract

Dimethylaminium (DMA+) and trimethylaminium (TMA+) ions in size-segregated atmospheric particles are measured across the marginal seas of China and the northwest Pacific Ocean (NWPO) in March–May 2014. The concentrations of DMA+ and TMA+ in particles with diameters of 0.056–10 μm (PM0.056–10) collected from the eutrophic seas are 0.22 ± 0.38 nmol/m3 and 0.11 ± 0.23 nmol/m3, respectively. Surprisingly, an average TMA+ concentration that is 1 order of magnitude higher and a slightly higher average DMA+ concentration are observed across the oligotrophic NWPO. However, the concentrations of chlorophyll-a in the NWPO are approximately 5 times lower than those in the marginal seas. The maximum concentrations of TMA+ (4.39 nmol/m3) and DMA+ (0.92 nmol/m3) in PM0.056–10 are observed close to the largest cyclonic eddy in the NWPO under an average wind speed of 14 m/s. The concentrations of TMA+ increase with decreasing particle size in the sample, whereas those of DMA+ exhibit a condensation mode at 0.2 μm and a droplet mode at 1–2 μm. The bimodal size distribution of DMA+ is conventionally interpreted in terms of secondary reactions in the atmosphere. The unique size distribution of TMA+ suggests that it very likely originates from sea-spray aerosols. Based on their size distributions in other samples collected over the NWPO, these conclusions may generally apply for TMA+ and DMA+. Moreover, we propose a novel conceptual model to explain how the largely increased primary TMA+ and secondary DMA+ are linked to emissions of sea-spray aerosols and gaseous precursors from various cyclonic eddies.