Transport and production of NO_<i>X</i> in electrified thunderstorms: Survey of previous studies and new observations at midlatitudes

Abstract

First airborne NO x (NO+NO 2 ) measurements in anvils of active thunderstorms in Europe were performed in summer 1996 over southern Germany and Switzerland (47°‐49°N). This field experiment LINOX (lightning‐produced NO x ) was designed to study the production of NO x by lightning discharges and the transport in convective storms. With the research aircraft Falcon of the Deutsches Zentrum für Luft‐ und Raumfahrt, about 20 anvil penetrations were performed including measurements of NO, NO 2 , CO 2 , O 3 , and meteorological parameters. In thunderstorm anvils, mean NO x mixing ratios between 0.8 and 2.2 ppbv were measured with peak values reaching up to 4 ppbv. A considerable part of these enhancements could be attributed to the transport of polluted air from the planetary boundary layer (PBL) using CO 2 as tracer for PBL air. NO x produced by lightning can be obtained by subtracting the fraction of NO x transported from the PBL from total NO x measured in the anvil. The NO x /CO 2 correlation in larger cumulus clouds without lightning was used as reference for the transport of PBL air in the anvils. In smaller LINOX thunderstorms the contribution from lightning, respectively, PBL transport to anvil NO x , was about equal. However, in medium and large LINOX thunderstorms the contribution from lightning dominated (60–75%). For these kind of thunderstorms it was estimated that ∼1.0±0.5 ppbv NO x resulted from lightning production. The observations were used to quantify the NO x production per thunderstorm and to give a rough estimate of the annual production of NO x . For the global lightning nitrogen budget the uncertainties were considerable (0.3–22 Tg(N) yr −1 ). The mean value for the global NO x production rate by lightning in the upper troposphere was estimated to 4 Tg(N) yr −1 .