Seasonal variations of C 1 -C 4 alkyl nitrates at a coastal site in Hong Kong: Influence of photochemical formation and oceanic emissions

Five C -C alkyl nitrates (RONO ) were measured at a coastal site in Hong Kong in four selected months of 2011 and 2012. The total mixing ratios of C -C RONO (Σ RONO ) ranged from 15.4 to 143.7 pptv with an average of 65.9 ± 33.0 pptv. C -C RONO (2-butyl nitrate and 2-propyl nitrate) were the most abundant RONO during the entire sampling period. The mixing ratios of C -C RONO were higher in winter than those in summer, while the ones of methyl nitrate (MeONO ) were higher in summer than those in winter. Source analysis suggests that C -C RONO were mainly derived from photochemical formation along with biomass burning (58.3-71.6%), while ocean was a major contributor to MeONO (53.8%) during the whole sampling period. The photochemical evolution of C -C RONO was investigated, and found to be dominantly produced by the parent hydrocarbon oxidation. The notable enrichment of MeONO over C -C RONO was observed in a summer episode when the air masses originating from the South China Sea (SCS) and MeONO was dominantly derived from oceanic emissions. In order to improve the accuracy of ozone (O ) prediction in coastal environment, the relative contribution of RONO from oceanic emissions versus photochemical formation and their coupling effects on O production should be taken into account in future studies.