EGUsphere EGUsphere EGUsphere EGUsphere 1680-7375 Copernicus Publications Göttingen, Germany 10.5194/egusphere-2024-951 Impact of improved representation of VOC emissions and production of NO<sub>x</sub> reservoirs on modeled urban ozone production Travis Katherine R. https://orcid.org/0000-0003-1628-0353 1 Nault Benjamin A. https://orcid.org/0000-0001-9464-4787 2 3 Crawford James H. 1 Bates Kelvin H. https://orcid.org/0000-0001-7544-9580 4 Blake Donald R. 5 Cohen Ronald C. https://orcid.org/0000-0001-6617-7691 6 7 Fried Alan 8 Hall Samuel R. 9 Huey L. Greg https://orcid.org/0000-0002-0518-7690 10 Lee Young Ro 11 Meinardi Simone 5 Min Kyung-Eun 12 Simpson Isobel J. 5 Ullman Kirk 9 NASA Langley Research Center, Hampton, VA, USA CACC, Aerodyne Research, Inc., Billerica, MA, USA Department of Environmental Health and Engineering, Johns Hopkins University, Baltimore, MD, USA NOAA Chemical Sciences Laboratory, Earth System Research Laboratories, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80305, USA Department of Chemistry, University of California, Irvine, Irvine CA USA 92697 Department of Chemistry, University of California, Berkeley, CA, USA Department of Earth and Planetary Science, University of California, Berkeley, CA, USA INSTAAR, University of Colorado, Boulder, CO, USA Atmospheric Chemistry Observations & Modeling Laboratory, NCAR, Boulder, CO, USA School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA School of Environmental Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, South Korea 08 04 2024 2024 1 27 Copyright: © 2024 Katherine R. Travis et al. 2024 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2024/egusphere-2024-951/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2024/egusphere-2024-951/egusphere-2024-951.pdf

The fraction of urban volatile organic compounds (VOC) emissions attributable to fossil fuel combustion has been declining in many parts of the world, resulting in a need to better constrain other anthropogenic sources of these emissions. During the National Institute of Environmental Research (NIER) and National Aeronautics and Space Administration (NASA) Korea-United States Air Quality (KORUS-AQ) field study in Seoul, South Korea during May&ndash;June 2016, air quality models underestimated ozone, formaldehyde, and peroxyacetyl nitrate (PAN) indicating an underestimate of VOCs in the emissions inventory. Here, we use aircraft observations interpreted with the GEOS-Chem chemical transport model to assess the need for increases in VOC emissions. We find that the largest increases are attributable to compounds associated with volatile chemical products, liquefied petroleum gas (LPG) and natural gas emissions, and long-range transport. Revising model chemistry to better match observed VOC speciation together with increasing model emissions of underestimated VOC species increased calculated OH reactivity by +2 s<sup>-1</sup> and ozone production by 2 ppb hr<sup>-1</sup>. Ozone increased by 6 ppb below 2 km and 9 ppb at the surface, and formaldehyde and acetaldehyde increased by 30 % and 120 % aloft, respectively, all in better agreement with observations. The larger increase in acetaldehyde was attributed to ethanol emissions which we found to be as important for ozone production as isoprene or alkenes. The increased acetaldehyde largely resolved the model PAN bias. The need for additional unmeasured VOCs however was indicated by a remaining model bias of -1 ppb in formaldehyde and 57 % and 52 % underestimate in higher peroxynitrates (PNs) and alkyl nitrates (ANs), respectively. We added additional chemistry to the model to represent an additional six PNs from observed VOCs but were unable to account for the majority of missing PNs. However, four of these PNs were modeled at concentrations similar to other commonly measured PNs (&gt;2 % of PAN) indicating that these should be measured in future campaigns. We hypothesize that emissions of oxygenated VOCs (OVOCs) such as &gt;C5 aldehydes from cooking and/or alkenes associated with volatile chemical products could produce both PNs and ANs and improve remaining model biases. Emerging research on the emissions and chemistry of these species will soon allow for modeling of their impact on local and regional photochemistry.

 National Aeronautics and Space Administration 80NSSC22K0283 NNX15AT99G NNX15AT92G