Secondary Formation and Impacts of Gaseous Nitro-Phenolic Compounds in the Continental Outflow Observed at a Background Site in South China br

Nitro-phenolic compounds (NPs) have attractedincreasing attention because of their health risks and impacts onvisibility, climate, and atmospheric chemistry. Despite manymeasurements of particulate NPs, the knowledge of their gaseousabundances, sources, atmospheric fates, and impacts remainsincomplete. Here, 18 gaseous NPs were continuously measuredwith a time-of-flight chemical ionization mass spectrometer at abackground site in South China in autumn and winter. AbundantNPs were observed in the continental outflows from East Asia,with a total concentration up to 122.1 pptv. Secondary formationfrom the transported aromatics dominated the observed NPs, withmono-NPs exhibiting photochemical daytime peaks and nighttimeenrichments of di-NPs and Cl-substituted NPs. The budgetanalysis indicates that besides the center dot OH oxidation of aromatics, the NO3 center dot oxidation also contributed significantly to the daytimemono-NPs, while the further oxidation of mono-NPs by NO3 center dot dominated the nocturnal formation of di-NPs. Photolysis was themain daytime sink of NPs and produced substantial HONO, which would influence atmospheric oxidation capacity in downwindand background regions. This study provides quantitative insights on the formation and impacts of gaseous NPs in the continentaloutflow and highlights the role of NO3 center dot chemistry in the secondary nitro-aromatics production that may facilitate regional pollution.