Characterization of nitroaromatic compounds in atmospheric particulate matter from Beijing

Nitroaromatic compounds (NACs) have received much attention as a kind of toxic and important light-absorbing components in atmospheric PM2.5. In order to clarify the chemical composition, concentration levels and sources of NACs in the atmosphere, PM2.5 samples were collected from April 2016 to April 2017 in Beijing. Selective and non-targeted analytical method based on liquid chromatography-Orbitrap MS (LC-Orbitrap MS) was used to characterize atmospheric NACs for the first time. A total of 190 NACs were quantified and semi-quantified with authentic standards or surrogates, of which 165 NACs were identified tentatively. Nitro-polyaromatic compounds (NPCs) were identified and semi-quantified for the first time, including nitronaphthol, nitroacenaphthenol, nitrofluorenol, nitroaceanthrylenol, nitropyrenol and their methyl derivatives, etc. The seasonal average concentrations of total NACs were from 10.8 in summer to 100 ng/m(3) in winter, which was higher than in many other areas. Nitrophenols (NP) and nitrocatechols (NC) were the most abundant NACs species, and the proportion to total NACs were 31% and 32%, respectively. The seasonal average concentration of NPCs ranged from 1.5 in summer to 9.6 ng/m(3) in winter with an annual average contribution of 12%, which cannot be ignored. In winter, the contribution of NACs to organic matter (OM) and PM2.5 were up to 2.88 parts per thousand and 1.59 parts per thousand, respectively. Four major sources were assigned, coal combustion and secondary formation had the highest contribution of 35%, followed by biomass combustion (32%), dust (18%), and transportation (6%).

Automated summary

The study collected PM2.5 samples in Beijing and characterized atmospheric NACs for the first time using LC-Orbitrap MS technology, identifying and quantifying 165 out of 190 NACs, as well as nitro-polyaromatic compounds. Nitrophenols and nitrocatechols were the most abundant NACs species, accounting for 31% and 32% of total NACs, respectively. The study also found that NACs had a significant contribution to organic matter and PM2.5 in winter, with major sources identified as coal combustion, biomass combustion, dust, and transportation.