Characterization and possible sources of nitrated mono- and di-aromatic hydrocarbons containing hydroxyl and/or carboxyl functional groups in ambient particles in Nagoya, Japan

By understanding the sources and temporal variations of nitrated mono- and di-aromatic hydrocarbons (nitroaromatic hydrocarbons, NAHCs) in ambient particles, we can evaluate their impact on the climate, environment, and human health. This work quantifies (for the first time) a series of NAHCs (3,5-dinitrosalicylic acid, 2,4-dinitro-1-naphthol, 4-nitrophthalic acid, and 2-hydroxy-5-nitrobenzyl alcohol) in ambient particles collected from an urban site in Nagoya, Japan. The data were collected throughout the day/night cycles during the summer and fall of 2013. To evaluate the possible sources of the NAHCs, the observed NAHC concentrations were compared with organic tracers of anthropogenic secondary organic aerosols (ASOAs) and biomass buming. Nitrocatechols were mainly influenced by emissions from biomass burning during the fall, and by secondary formation from anthropogenic volatile organic compounds (AVOCs) during the summer. In both seasons, AVOC oxidation mainly produced nitrosalicylic acids, 4-nitro-1-naphthol, and 4-nitrophthalic acid, whereas biomass burning in the fall produced a significant amount of 4-nitro-1-naphthol. The concentrations of 3,5-dinitrosalicylic acid and 4-nitrophthalic acid were highly correlated with those of other ASOA tracers, and were strongly related to wind direction, oxidant concentration, and solar radiation. Therefore, these NAHCs are suggested as new tracers of ASOA. Meanwhile, although 2-hydroxy-5-nitrobenzyl alcohol was generated by AVOCs photo-oxidation during the day, its concentration remained high at night, indicating additional nighttime sources such as nitrate radical reactions. Our results suggest that different NAHCs could have different sources, large seasonal and day-to-night variations in their major ones.