Lightning NOx influence on large-scale NOy and O3 plumes observed over the northern mid-latitudes

This paper describes the NO_y plumes originating from lightning emissions based on 4 yr (2001–2005) of MOZAIC measurements in the upper troposphere of the northern mid-latitudes, together with ground- and space-based observations of lightning flashes and clouds. This analysis is primarily for the North Atlantic region where the MOZAIC flights are the most frequent and for which the measurements are well representative in space and time. The study investigates the influence of lightning NO_x (LNO_x) emissions on large-scale (300–2000 km) plumes (LSPs) of NO_y. One hundred and twenty seven LSPs (6% of the total MOZAIC NO_y dataset) have been attributed to LNO_x emissions. Most of these LSPs were recorded over North America and the Atlantic mainly in spring and summer during the maximum lightning activity occurrence. The majority of the LSPs (74%) is related to warm conveyor belts and extra-tropical cyclones originating from North America and entering the intercontinental transport pathway between North America and Europe, leading to a negative (positive) west to east NO_y (O₃) zonal gradient with −0.4 (+18) ppbv difference during spring and −0.6 (+14) ppbv difference in summer. The NO_y zonal gradient can correspond to the mixing of the plume with the background air. On the other hand, the O₃ gradient is associated with both mixing of background air and with photochemical production during transport. Such transatlantic LSPs may have a potential impact on the European pollution. The remaining sampled LSPs are related to mesoscale convection over Western Europe and the Mediterranean Sea (18%) and to tropical convection (8%).