Exploring ozone production sensitivity to NOₓ and VOCs in the New York City airshed in the spring and summers of 2017–2019

Abstract

Reducing ozone in the New York City (NYC) region requires understanding the nonlinearity of ozone production (PO₃) and its sensitivity to volatile organic compounds (VOCs) and nitrogen oxides (NOₓ = NO₂ + NO). Using observations from the Long Island Sound Tropospheric Ozone Study (LISTOS) in the late spring and summers of 2017–2019 and a 0-D box model, we test the sensitivity of PO₃ to ozone precursors. PO₃ is greater in the morning than the afternoon due to increased concentrations of NO₂ and VOC. This diurnal variation in PO₃ is enhanced in the late summer. Based on the model response of PO₃ to changes in initial NO₂, 14% of samples are within a VOC-limited regime. The metric LROₓ/LNOₓ, which compares the radical loss rates via self-reaction to their reaction with NO₂, indicates an additional 17% of samples are in transition between NOₓ and VOC-limited regimes (0.30 <= LROₓ/LNOₓ <= 1). We often find PO₃ to be VOC-limited in NYC and along the Connecticut coastline (I-95 corridor). In these samples, PO₃ is most sensitive to isoprene, propene, and isopentane, and individual VOCs have strong diurnal and seasonal variations. We further compare PO₃ calculations using the near explicit Master Chemical Mechanism (MCMv3.3.1) and Carbon Bond 6 revision 2 (CB6r2) for a more direct link to regulatory air quality models. Modeled PO₃ is 20% greater in MCMv3.3.1, due largely to the speciation of VOC and organic peroxy radicals, however the bounds of LROₓ/LNOₓ used to determine the transition range between PO₃ regimes remain the same.