Citation:

Kenagy, H., P. Romer, P. Wooldridge, B. Nault, P. Campuzano-Jost, D. Day, J. Jimenez, A. Zare, H. Pye, J. Yu, C. Song, D. Blake, J. Woo, Y. Kim, AND R. Cohen. Contribution of Organic Nitrates to Organic Aerosol over South Korea during KORUS-AQ. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 55(24):16326–16338, (2021). https://doi.org/10.1021/acs.est.1c05521

Impact/Purpose:

Organic nitrates serve as a temporary reservoir of nitrogen oxides (NOx) in the atmosphere. Release of NOx catalyzes formation of ozone while deposition of organic nitrates or conversation to nitric acid removes oxidized nitrogen from the atmosphere. This work finds a large missing source of semivolatile organic nitrates in the CMAQ model for conditions above Korea.

Description:

The role of anthropogenic NOx emissions in secondary organic aerosol (SOA) production is not fully understood but is important for understanding the contribution of emissions to air quality. Here, we examine the role of organic nitrates (RONO2) in SOA formation over the Korean Peninsula during the Korea–United States Air Quality field study in Spring 2016 as a model for RONO2 aerosol in cities worldwide. We use aircraft-based measurements of the particle phase and total (gas + particle) RONO2 to explore RONO2 phase partitioning. These measurements show that, on average, one-fourth of RONO2 are in the condensed phase, and we estimate that ≈15% of the organic aerosol (OA) mass can be attributed to RONO2. Furthermore, we observe that the fraction of RONO2 in the condensed phase increases with OA concentration, evidencing that equilibrium absorptive partitioning controls the RONO2 phase distribution. Lastly, we model RONO2 chemistry and phase partitioning in the Community Multiscale Air Quality modeling system. We find that known chemistry can account for one-third of the observed RONO2, but there is a large missing source of semivolatile, anthropogenically derived RONO2. We propose that this missing source may result from the oxidation of semi- and intermediate-volatility organic compounds and/or from anthropogenic molecules that undergo autoxidation or multiple generations of OH-initiated oxidation.

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