Photostationary state deviation-estimated peroxy radicals and their implications for HO < inf> x and ozone photochemistry at a remote northern Atlantic coastal site

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Measurements of NO, NO2, O3, and ultraviolet irradiance made at Cape Norman, Newfoundland (51.6°N, 55.9°W), during February-April 1996 were used to examine peroxy radical photochemistry and the local photochemical ozone tendency. Deviations from NO-NO2-O3 photostationary state (the PSSD method) were used to estimate peroxy radical (PO2) mixing ratios. Potential biases in the PSSD method and the methods used to apply it in an unbiased manner are discussed. PO2 levels reached 77 ± 8 pptv (midday mean ±2σ of the mean), significantly higher than observed in previous studies at remote marine locations. [PO2] was well correlated with (JO1D)1/2, indicating that the dominant radical source was photolysis by ultraviolet radiation in the wavelength region of O3 photolysis and the dominant sink of PO2 was recombination. However, the variation of [PO2] with (JO1D1/2 (d[PO2]/d(JO1D1/2) was significantly higher than expected at this site during spring. Significant radical production in addition to that from net O3 photolysis, possibly related to snow photochemistry in the upwind region, is suggested as the cause. However, the measurements needed to test this hypothesis were not made in this study, and we suggest future HOx measurements in remote midlatitude, snow-covered regions. The net photochemical ozone production at this site during springtime was calculated to be minimal (generally small and negative, and always less than or equal to +0.1 ppbv/h). These small values indicate that in situ photochemical ozone production is negligible at this site during spring; if [HO2]/[PO2] is large, net ozone destruction may contribute up to ~10% of mean ozone levels per day. Copyright 2004 by the American Geophysical Union.

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Journal of Geophysical Research: Atmospheres