Ozone Formation under high NOx conditions: Insights from the AEROMMA NYC-METS field campaign

Despite well over a half century of research, gaps remain in our understanding of ozone formation chemistry. Net ozone formation results from the oxidation of NO to NO₂ by peroxy radicals (HO₂ and RO₂) followed by photolysis of NO₂. Measurements of peroxy radicals made by several analytical methods over the past decade in numerous locations across the world have revealed discrepancies under high NOx conditions ([NO] > 1 ppb), with zero-dimensional models apparently underestimating peroxy radical concentrations and ozone production rates (P(O₃)) by up to a factor of eight. These findings suggest that models may misidentify when ozone formation is NOx-limited vs. NOx-saturated (VOC-limited) and that our knowledge of the relevant reactions is incomplete. To investigate these anomalously high P(O₃) values at high NOx, we used the Drexel University Ethane Chemical AMPlifier (ECHAMP) instrument to measure total peroxy radicals at a roof-top site in Manhattan (NYC) as part of the NOAA AEROMMA/NYC-METS project.  A wide assortment of other measurements were made by spectroscopic and mass spectrometric methods. We will present results from this field project with special emphasis on our measurements during a few “high-NOx” periods (roughly defined as daytime periods with NO mixing ratios greater than 1 ppb).