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

Estimates of the photochemical ozone generation rate, PQ, and the ozone production efficiency (OPE) per molecule of NOx (=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 PQ ∝ [NOx]–n + 1, ΔP ∝ [NOx]–n, n = 0.82 ± 0.06 (the determination coefficient R2 = 0.66), which correspond to the NOx-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.NOx] agrees with the OPE value of 39.8 [mol.O3/mol.NOx] obtained from the numerical experiments using the GEOS-chem global transport-chemical model. The observation data indicate the significant role of anthropogenic emissions of NOx 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.