Chemical Composition and Sources of Marine Aerosol over the Western North Pacific Ocean in Winter

Abstract

Atmospheric deposition of long-range transported continental substances from natural and anthropogenic sources affects biogeochemical processes in marine systems. Emissions of sea spray contribute aerosol particles to the marine atmosphere. Despite the importance of continental dispersion and atmospheric processes involving aerosol particles within remote marine atmosphere, knowledge of the sources of various water-soluble ions is limited because of insufficient observations. Concentrations of Total suspended particulates (TSPs) and major inorganic ions (Cl−, Na+, SO42−, Mg2+, Ca2+, K+, NO3−, NH4+), as well as organic nitrogen (ON-N) values, were measured in marine aerosol collected over the western north Pacific (WNP) during a cruise from 3 December 2014 to 13 March 2015. Aerosol samples were analyzed to determine their chemical characteristics and a source apportionment for this region and the continental influence on the open ocean when air masses are from continent in winter. TSP mass concentrations ranged from 14.1 to 136.0 μg/m3 with an average of 44.8 ± 28.1 μg/m3. Concentrations of TSPs and major ions were higher near the coast (close to Qingdao and Xiamen) and lower over the open ocean. The total mass of inorganic ions and organic nitrogen accounted for 51.1% of the total TSP. Cl− had highest concentrations among the major inorganic ions, followed by SO42−, NO3−, Mg2+, Ca2+, K+, and NH4+, respectively. However, Cl− showed a deficit relative to Na+ in most samples, likely related to heterogeneous reactions within the marine atmosphere. Most SO42−, Mg2+, Ca2+, and K+ were from sea salt, while other major ions were from continental sources. The non-sea-salt (nss) fractions of Ca2+, Mg2+ and K+ were derived from continental crust, while nss-SO42− and NO3− were derived from anthropogenic sources. ON had several sources, including reactions of NOx with volatile organic compounds (anthropogenic sources) or NH3 with gaseous hydrocarbons, as well as crustal and marine biogenic sources.

Particulate nitrate photolysis in the atmosphere

“…105–107 Nitrate are often internally mixed with chloride ions in the atmosphere through the chloride depletion reactions of sea spray particles. According to field measurements, the molar ratio of halides to nitrate in fresh sea spray aerosol is usually higher than 1.0, 108–112 whereas that in urban aerosol or aged marine aerosol falls in the range of 0–1.1. 113–117 Wingen et al reported that the coexistence of chloride ions results in an enhanced gaseous NO 2 production from deliquesced nitrate aerosol particles under illumination by a factor of 1.6 to 2.4.…”

Enhanced Sulfate Production by Nitrate Photolysis in the Presence of Halide Ions in Atmospheric Particles

“…47−53 We found that at [Cl − ]/[NO 3 − ] > 1.0, the halide-enhanced nitrate photolysis had little influence on the sulfate production due to the reduced nitrate concentration, and thus may not be important in fresh marine/coastal aerosols. The low concentration levels of nitrate in fresh marine aerosol (1−2 μg/m 3 ) 47,48,51 may also make the halideenhanced nitrate photolysis less relevant than in inland or urban aerosol. 43,44,46 On the other hand, aged sea-salt aerosols due to the chloride depletion reactions can result in lower [Cl − ]/[NO 3 − ] ratios, increasing the enhancement effect.…”

Physico-chemical characterization of urban aerosols from specific combustion sources in West Africaat Abidjan in Côte d’Ivoire and Cotonou in Benin in the frame of DACCIWA program

“…Our analysis also shows that Clin coarse and fine fractions are highly correlated with Mg 2+ (0.97 in wet season and 0.96 in dry season) combining all sites, except at ADF for which these correlation coefficients decrease to 0.68 and 0.95 in the wet and dry season, respectively. As Cl -, Na + and Mg 2+ are associated with sea salt origin or secondary aerosol production (Xiao et al, 2018), these results indicate that coarse Cl -, Na + and Mg 2+ particles (>1μm) from this study have the same "sea salt" origin at AT, CT, and CT, which is different at the ADF site. Their abundance in the wet season could be related to the influence of the predominant wind direction mainly oriented towards the North-East ( Figure 5) which transports marine aerosols to these sites.…”