Flights of the NASA DC-8 aircraft were conducted from Bangor, Maine over the Canadian maritime provinces during SONEX (SASS (Subsonic Assessment) Ozone and Nitrogen Oxides Experiment) in early November 1997. Surprisingly large NO and NOy mixing ratios were measured in the upper troposphere on these flights. We have performed detailed analyses of the data from two flights with the objective of determining the primary NOy contributors for the air encountered on various flight segments. Chemical signatures in the data (NO, NOy, CO, aerosol, hydrocarbons, peroxides, HNO3 and PAN) are revealed through examination of the data time series and through correlation analysis. The signatures are suggestive of convective transport of boundary layer pollution, lightning NOx production, and aircraft emissions.
Trajectory analyses along with satellite-derived convective cloud statistics, ground-based lightning flash detection data, and a detailed aircraft emission inventory are used to support the characteristic source signatures and draw conclusions concerning the dominant NOy source on various flight segments. On the November 3 flight, a major contribution to the upper tropospheric measurements appears to have originated from convective transport of polluted air over the southeastern U. S. approximately 1.5 days upstream. Later in the same flight closer convective activity with lightning over the Atlantic likely contributed to enhancements of NO and CO. Measurements of NOy on the November 9 flight were dominated by the lightning contribution from marine convection within and south of the flight region. This flight occurred shortly after a peak in the air traffic in the North Atlantic Flight Corridor, and an aircraft contribution to the measured NOy appears likely in the data.
Symposium on Interdisciplinary Issues in Atmospheric Chemistry