[1] 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 (>30,000 particles STP cm À3 ) 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 À1 ) in comparison to lightning production ($0.03 TgN yr À1 ). On the global scale, NO x produced by lightning (mean 3 TgN yr À1 ) prevails over aircraft-produced NO x (0.6 TgN yr À1 ).

First airborne NOx (NO+NO2) measurements in anvils of active thunderstorms in Europe were performed in summer 1996 over southern Germany and Switzerland (47ø-49øN). This field experiment LINOX (lightning-produced NOx) was designed to study the production of NOx by lightning discharges and the transport in convective storms. With the research aircraft Falcon of the Deutsches Zentrum ffir Luft-und Raumfahrt, about 20 anvil penetrations were performed including measurements of NO, NO2, CO2, 03, and meteorological parameters. In thunderstorm anvils, mean NOx 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 CO2 as tracer for PBL air. NOx produced by lightning can be obtained by subtracting the fraction of NOx transported from the PBL from total NOx measured in the anvil. The NOx/CO2 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 NOx, 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 NOx resulted from lightning production. The observations were used to quantify the NOx production per thunderstorm and to give a rough estimate of the annual production of NOx. For the global lightning nitrogen budget the uncertainties were considerable (0.3-22 Tg(N) yr-•). The mean value for the global NOx production rate by lightning in the upper troposphere was estimated to 4 Tg(N) yr -• 28,247 28,248 HUNTRIESER ET AL.: NOx IN ELECTRIFIED THUNDERSTORMS

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In late winter/early spring, sunrise after the polar night, followed by photodissociation oI HNO3 leads to formation o• Nt) x and, via reaction (1), of C1ONO 2. This is expected to shift the partitioning within NOy towards NOx and C1ONO 2 and to a decrease of the HNO3 fraction within NOy. This paper reports on measurements of HNO 3, NOy, N20 , and 03 during two aircraft campaigns in winter 1997 in the Arctic lower stratosphere. We focus on a strong reduction of the ratio HNO3/NOy observed from January to March.