Abstract. Organic nitrates are important atmospheric species that
significantly affect the cycling of NOx and ozone production. However,
characterization of particulate organic nitrates and their sources in
polluted atmosphere is a big challenge and has not been comprehensively
studied in Asia. In this study, an aerodyne high-resolution time-of-flight
aerosol mass spectrometer (HR-ToF-AMS) was deployed at an urban site in
China from 2015 to 2016 to characterize particulate organic nitrates in
total nitrates with a high time resolution. Based on the cross-validation of
two different data processing methods, organic nitrates were effectively
quantified to contribute a notable fraction of organic aerosol (OA), namely
9 %–21 % in spring, 11 %–25 % in summer, and 9 %–20 % in autumn, while contributing a very
small fraction in winter. The good correlation between organic nitrates and
fresh secondary organic aerosol (SOA) at night, as well as the diurnal trend
of size distribution of organic nitrates, indicated a key role of nighttime
local secondary formation of organic nitrates. Furthermore, theoretical
calculations of nighttime SOA production of NO3 reactions with volatile
organic compounds (VOCs) measured during the spring campaign were performed,
resulting in three biogenic VOCs (α-pinene, limonene, and camphene)
and one anthropogenic VOC (styrene) identified as the possible key VOC
precursors to particulate organic nitrates. The comparison with similar
studies in the literature implied that nighttime particulate organic
nitrate formation is highly relevant to NOx levels. This study proposes
that unlike the documented cases in the United States and Europe, modeling
nighttime particulate organic nitrate formation in China should incorporate
not only biogenic VOCs but also anthropogenic VOCs for urban air pollution,
which needs the support of relevant smog chamber studies in the future.
Supplementary material to "Characterization of nighttime formation of particulate organic nitrates based on high-resolution aerosol mass spectrometry in an urban atmosphere in China"
