Airborne measurements of NO sub(x), tracer species, and small particles during the European Lightning Nitrogen Oxides Experiment

Airborne in situ measurements of NO, NO sub(2), NO sub(y), CO, CO sub(2), O sub(3), J(NO sub(2)), and CN were performed in European thunderstorms during the field experiment EULINOX in July 1998. The measurements in the upper troposphere show enhanced NO sub(x) (= NO + NO sub(2)) concentrations within thunderstorms and their outflow at horizontal scales from 300 m to several 100 km. The maximum NO mixing ratio measured inside a thundercloud close to lightning (the aircraft was also hit by a small lightning strike) was 25 ppbv. A regional NO sub(x) enhancement of 0.5 ppbv over central Europe could be traced back to a thunderstorm event starting 24 hours earlier over Spain. The fractions of NO sub(x) in thunderclouds which are produced by lightning and convectively transported from the polluted boundary layer are determined by using CO sub(2) and CO as tracers for boundary layer air. The analyses show that on average about 70% of the NO sub(x) increase measured in the anvil region was found to result from production by lightning and about 30% from NO sub(x) in the boundary layer. Thunderstorms are also strong sources of small particles. The peak CN concentrations measured within thunderstorm outflows (>30,000 particles STP cm super(-3)) were distinctly higher than in the polluted boundary layer. The amount of NO sub(x) produced per thunderstorm and NO produced per lightning flash was estimated. The results imply that the annual mean NO sub(x) budget in the upper troposphere over Europe is dominated by aircraft emissions (0.1 TgN yr super(-1)) in comparison to lightning production (0.03 TgN yr super(-1)). On the global scale, NO sub(x) produced by lightning (mean 3 TgN yr super(-1)) prevails over aircraft-produced NO sub(x) (0.6 TgN yr super(-1)).