Airborne measurements of NO_<i>x</i>, tracer species, and small particles during the European Lightning Nitrogen Oxides Experiment

Abstract

Airborne in situ measurements of NO, NO 2 , NO y , CO, CO 2 , O 3 , J (NO 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 x (= NO + NO 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 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 x in thunderclouds which are produced by lightning and convectively transported from the polluted boundary layer are determined by using CO 2 and CO as tracers for boundary layer air. The analyses show that on average about 70% of the NO x increase measured in the anvil region was found to result from production by lightning and about 30% from NO x in the boundary layer. Thunderstorms are also strong sources of small particles. The peak CN concentrations measured within thunderstorm outflows (&gt;30,000 particles STP cm −3 ) were distinctly higher than in the polluted boundary layer. The amount of NO x produced per thunderstorm and NO produced per lightning flash was estimated. The results imply that the annual mean NO x budget in the upper troposphere over Europe is dominated by aircraft emissions (0.1 TgN yr −1 ) in comparison to lightning production (∼0.03 TgN yr −1 ). On the global scale, NO x produced by lightning (mean 3 TgN yr −1 ) prevails over aircraft‐produced NO x (0.6 TgN yr −1 ).