Detection of lightning-produced NO in the midlatitude upper troposphere during STREAM 1998

Simultaneous in situ measurements of NO, NOy, HNO3, CO, CO2, O-3, and aeros ols were performed in the midlatitude upper troposphere (UT) and lower stra tosphere during the Stratosphere-Troposphere Experiment by Aircraft Measure ments (STREAM) 1998 summer campaign. The campaign focused on the region aro und Timmins in the Canadian province of Ontario (79.3 degreesW, 48.2 degree sN), close to the polar jet stream that rapidly transports trace species ac ross the Atlantic Ocean. This paper focuses on the origin of total reactive nitrogen (NOy) in the UT, as our measurements show strong variations, whic h reflect large local sources. In situ production by lightning, stratospher ic downdraft, aircraft emissions, and upward transport of polluted boundary layer air are discussed in two case studies as potential contributors. We use correlations among NO, NOy and CO to distinguish between transport from the boundary layer and in situ formations. Lightning production of NOx is found to be a strong contributor to the budget of NOy during high NOy episo des.