Regional Photochemical Surface-Ozone Sources in Europe and Western Siberia

Abstract

The influence of climatically significant regional sources of NO_x (=NO + NO₂), CO, and biogenic volatile organic compounds (VOCs) on the photochemical generation of surface ozone (O₃) in the lower troposphere over Europe and Siberia is studied. The sensitivity of the O₃ field to the total emissions of ozone precursors is calculated using a global 3D chemical transport model (GEOS-Chem) based on the 2007–2012 databases for anthropogenic (EDGAR) and biogenic (MEGAN, GFED) emissions. The amount of photochemical ozone generated during the summer months is in good correlation with the air-mass age determined from the ratio between \({\text{N}}{{{\text{O}}}_{x}}\) and (total reactive nitrogen) \({\text{N}}{{{\text{O}}}_{y}},\) when the mean contribution of regional sources is \({\Delta\text{}}{{{\text{O}}}_{{\text{3}}}}\) ~ 10–15 ppb, which is 20–30% of its background concentration in the middle latitudes (\({{{\text{O}}}_{{\text{3}}}}\) ~ 35–45 ppb). The quantitative estimates of the ozone production efficiency \({{{\Delta\text{}}{{{\text{O}}}_{{\text{3}}}}} \mathord{\left/ {\vphantom {{{\Delta\text{}}{{{\text{O}}}_{{\text{3}}}}} \Delta }} \right. \kern-0em} \Delta }{\text{(N}}{{{\text{O}}}_{y}} - {\text{N}}{{{\text{O}}}_{x}}{\text{)}}\) (\({\text{N}}{{{\text{O}}}_{y}}\) is the total reactive nitrogen) for the summer months of the indicated period (~10–30 mol O₃/mol NO_x) are in good agreement with the theory of photochemical ozone generation under the conditions of slightly polluted air.