To assess the relative contributions of traffic emission and other potential sources to high levels of atmospheric ammonia (NH) in urban areas in the wintertime, atmospheric NH and related pollutants were measured at an urban site, ∼300 m from a major traffic road, in northern China in November and December 2015. Hourly average NH varied from 0.3 to 10.8 ppb with an average of 2.4 ppb during the campaign. Contrary to the common perspective in literature, traffic emission was demonstrated to be a negligible contributor to atmospheric NH. Atmospheric NH correlated well with ambient water vapor during many time periods lasting from tens of hours to several days, implying NH released from water evaporation is an important source. Emissions from local green space inside the urban areas were identified to significantly contribute to the observed atmospheric NH during ∼60% of the sampling times. Evaporation of predeposited NH through wet precipitation combined with emissions from local green space likely caused the spikes of atmospheric NH mostly occurring 1-4 h after morning rush hours or after and during slight shower events. There are still ∼30% of the data samples with appreciable NH level for which major contributors are yet to be identified.

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In 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.

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 (PM 0.056-10 ) collected from the eutrophic seas are 0.22 ± 0.38 nmol/m 3 and 0.11 ± 0.23 nmol/m 3 , 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/m 3 ) and DMA + (0.92 nmol/m 3 ) in PM 0.056-10 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.

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