The NOx-Limiting Regime of Photochemical Ozone Generation in a Weakly Polluted Convective Boundary Layer: Observations at the ZOTTO Tall Tower Observatory in Central Siberia, 2007–2015

Abstract

Estimates of the photochemical ozone generation rate, P_Q, and the ozone production efficiency (OPE) per molecule of NO_x (=NO + NO₂), ∆P, are obtained for the region of Central Siberia based on near surface observations of the concentrations of ozone (O₃) and nitrogen oxides (NO and NO₂) at ZOTTO (Zotino Tall Tower Observatory) in 2007–2015. The experimental data are approximated well by the power dependences P_Q ∝ [NO_x]^–n + 1, ΔP ∝ [NO_x]^–n, n = 0.82 ± 0.06 (the determination coefficient R² = 0.66), which correspond to the NO_x-limiting regime of ozone generation in a weakly polluted air mass. The average value for the summer months ΔP ~ 30.0–43.7 [mol.O₃/mol.NO_x] agrees with the OPE value of 39.8 [mol.O₃/mol.NO_x] obtained from the numerical experiments using the GEOS-chem global transport-chemical model. The observation data indicate the significant role of anthropogenic emissions of NO_x in the regional ozone balance and the necessity of taking this factor into account in predicting ecological risks in the Siberian regions that are traditionally regarded as ecologically pure.