Evidence of Nighttime Production of Organic Nitrates During SEAC⁴RS, FRAPPÉ, and KORUS‐AQ

Abstract

Organic nitrates (RONO2) are an important NOx sink. In warm, rural environments dominated by biogenic emissions, nocturnal NO3‐initiated production of RONO2 is competitive with daytime OH‐initiated RONO2 production. However, in urban areas, OH‐initiated production of RONO2 has been assumed dominant and NO3‐initiated production considered negligible. We show evidence for nighttime RONO2 production similar in magnitude to daytime production during three aircraft campaigns in chemically distinct summertime environments: Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS) in the rural Southeastern United States, Front Range Air Pollution and Photochemistry Experiment (FRAPPÉ) in the Colorado Front Range, and Korea‐United States Air Quality Study (KORUS‐AQ) around the megacity of Seoul. During each campaign, morning observations show RONO2 enhancements at constant, near‐background Ox (≡ O3+NO2) concentrations, indicating that the RONO2 are from a non‐photochemical source, whereas afternoon observations show a strong correlation between RONO2 and Ox resulting from photochemical production. We show that there are sufficient precursors for nighttime RONO2 formation during all three campaigns. This evidence impacts our understanding of nighttime NOx chemistry.

Vertically Resolved Aerosol Chemistry in the Low Boundary Layer of Beijing in Summer

“…One possible explanation was the different formation mechanisms of LO-OOA in summer and winter. Although LO-OOA was dominantly from oxidation of anthropogenic VOCs, for example, organic nitrates from NO 3 oxidation at nighttime in winter due to low emissions of biogenic VOCs, it could have a large contribution from oxidation of biogenic VOCs in summer . Indeed, previous studies found that the monoterpene- and sesquiterpene-derived SOA decreased and the anthropogenic SOA from toluene oxidation increased with the increase in the height in the city …”

First Online Observation of Aerosol Total Organic Nitrogen at an Urban Site: Insights Into the Emission Sources and Formation Pathways of Nitrogenous Organic Aerosols

“…Hence, we inferred that the parallel increases of aerosol ON and IN during nighttime was most likely a result of the nocturnal chemistry involving NO 3 radical. It has been long realized that organic nitrates contribute importantly to OA mass, particularly those formed during nighttime involving the reactions between alkenes and NO 3 radical (Kenagy et al., 2020; Perring et al., 2013; Rollins et al., 2012; Xu et al., 2021). However, observation studies of organic nitrates in urban atmospheres are limited, especially in the megacities of China (Huang et al., 2021).…”

Evaluating the Impact of Chemical Complexity and Horizontal Resolution on Tropospheric Ozone Over the Conterminous US With a Global Variable Resolution Chemistry Model

“…Additionally, Kenagy et al. ( 2020 ) suggest that organic nitrate production from NO 3 ‐initiated VOC oxidation at night is comparable to that from OH‐initiated VOC oxidation during the day in the Southeast US. Further evaluation of how well CESM/CAM‐chem represents the boundary layer and chemistry at night may also be needed to fully understand this organic nitrate model bias.…”