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

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.