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This study examined the observed summertime ozone production efficiency (OPE) and background ozone ([O3]) concentration at two rural sites in New York State, Pinnacle State Park (PSP) in Addison, NY, and Whiteface Mountain Summit (WFMS) in Wilmington, NY. Observed summertime OPEs and their relationship to oxides of nitrogen concentrations ([NOx]) were assessed during photochemically active periods at PSP and WFMS from 2000 to 2017 and 2015–2017, respectively. The summertime OPE increased in response to [NOx] reductions at PSP, consistent with a NOx‐sensitive regime for O3production. At PSP, the summertime OPE increased from approximately 5–7 parts per billion per parts per billion (ppb ppb−1) in 2000–2009 to approximately 13 ppb ppb−1in 2012–2017, and the median [NOx] concentration during photochemically productive periods decreased from about 0.60 ppb in 2000–2005 to about 0.23 ppb in 2012–2017. At WFMS, the summertime OPE was approximately 18 ppb ppb−1in 2015–2017, and the median [NOx] concentration during photochemically active periods from 2015 to 2017 was about 0.21 ppb. The higher WFMS summertime OPE is consistent for a site characterized by lower [NOx] concentrations. The summertime background [O3] concentration at PSP and WFMS was approximately 31–33 ppb for the analysis period, indicating that both sites were likely affected by similar regional emission sources. Ozone production efficiency at a rural New York State site over an 18‐year period increased in response to oxides of nitrogen reductionsOzone production efficiency was higher at the more remote site with lower oxides of nitrogen concentrationsSimilar summertime background ozone concentrations were observed for both sites

Simultaneous, in situ measurements of OH, HO2, H2O, and O3from 37–23 km are reported. The partitioning between OH and HO2and the total HOxconcentration are compared with expected steady‐state values. The ratio of HO2to OH varies from less than 2 at 36 km to more than 3 at 25 km; in the lower stratosphere this ratio is nearly a factor of two less than predicted. The data are used to calculate HOxproduction and loss rates. The measured HOxmixing ratio is consistent with production dominated by the reaction of O(1D) with H2O, and loss controlled by NOybelow 28 km and HOxabove 30 km. The steady‐state concentration of H2O2is inferred from the measured HO2concentration and calculated photolysis rate. The maximum H2O2mixing ratio (at 33 km) is predicted to be less than 0.2 ppb.

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are studied by using a low‐pressure discharge flow reactor with combined laser magnetic resonance and resonance fluorescence detection of atoms and molecules.