Regional Photochemical Surface-Ozone Sources in Europe and Western Siberia

The influence of climatically significant regional sources of NOx (=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 NOx) are in good agreement with the theory of photochemical ozone generation under the conditions of slightly polluted air.