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- Title
Size‐Dependent Nighttime Formation of Particulate Secondary Organic Nitrates in Urban Air.
- Authors
Huang, Wei; Huang, Ru‐Jin; Duan, Jing; Lin, Chunshui; Zhong, Haobin; Xu, Wei; Gu, Yifang; Ni, Haiyan; Chang, Yunhua; Wang, Xuan
- Abstract
Particulate secondary organic nitrates play a key role in understanding secondary organic aerosol production, ozone formation, and the atmospheric nitrogen cycle. However, the formation of particulate secondary organic nitrates in ambient air remains poorly understood. In this study, the nighttime formation processes of particulate secondary organic nitrates were investigated based on size‐resolved aerosols measured in urban air of China with a soot particle long‐time‐of‐flight aerosol mass spectrometer. The results show a bimodal size distribution of particulate secondary organic nitrates, peaking at ∼350 nm in condensation mode (100–400 nm) and ∼750 nm in droplet mode (400–2,500 nm), respectively. The nighttime formation processes of particulate secondary organic nitrates in the two size modes were respectively governed by temperature‐dependent condensation and aqueous‐phase processing. In particular, the mass concentration of particulate secondary organic nitrates in condensation mode was positively correlated with nitrate radical production and negatively correlated with temperature, suggesting that the formation processes were associated with the gas‐particle conversion of nitrate radical oxidation products. In contrast, the enhanced particulate secondary organic nitrates in droplet mode were predominantly contributed by aqueous‐phase processing, as indicated by the strong positive correlation with aerosol liquid water content and typical fragment ions from aqueous processing products (r = 0.52–0.59, P < 0.01). Our results highlight the potential of a size‐dependent mechanism to elucidate the formation processes of particulate secondary organic nitrates. Plain Language Summary: Particulate organic nitrates are an important nitrogen‐containing compound in the ambient atmosphere and have significant effects on air quality. However, the formation processes of particulate organic nitrates are complex in ambient air, leading to difficulties in understanding of their atmospheric processes and impacts. Here, nighttime formation of particulate secondary organic nitrates in different size particles is investigated in urban air. The results show that the nighttime formation pathways of particulate secondary organic nitrates in different size particles are distinct. Furthermore, aqueous processing plays an important role in the nighttime formation of particulate secondary organic nitrates in large size particles, especially in fog‐rain days. This information provides for a better understanding of the formation of particulate secondary organic nitrates in ambient air and is useful for future design of laboratory and atmospheric chemistry model studies. Key Points: Particulate secondary organic nitrates concentrations were significantly enhanced during fog‐rain days compared to non‐fog‐rain daysSize distributions of secondary organic nitrates were characterized by bimodal structure, peaking at ∼350 and ∼750 nm, respectivelyThe nighttime formation of organic nitrates in two size modes was respectively dominated by gas‐particle partitioning and aqueous processing
- Subjects
CHINA; PARTICULATE nitrate; ATMOSPHERIC nitrogen; NITRATES; ATMOSPHERIC chemistry; CHEMICAL models; NITROGEN cycle; DAUGHTER ions; COLLOIDAL carbon
- Publication
Journal of Geophysical Research. Atmospheres, 2023, Vol 128, Issue 18, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2022JD038189