Lightning-produced NO<sub>x</sub> over Brazil during TROCCINOX: airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems

Abstract

Abstract. During the TROCCINOX field experiments in February-March 2004 and February 2005, airborne in situ measurements of NO, NO y , CO, and O 3 mixing ratios and the J(NO 2 ) photolysis rate were carried out in the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature ( e ) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity in the upper troposphere within the Bolivian High (north of the subtropical jet stream). During thunderstorm anvil penetrations, typically at 20-40 km horizontal scales, NO x mixing ratios were distinctly enhanced and the absolute mixing ratios varied between 0.2-1.6 nmol mol −1 on average. This enhancement was mainly attributed to NO x production by lightning and partly due to upward transport from the NO x -richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NO x , CO and O 3 absolute mixing ratios were significantly enhanced in these air masses in the range of 0.6-1.1, 110-140 and 60-70 nmol mol −1 , respectively. AnalysesCorrespondence to: H. Huntrieser (heidi.huntrieser@dlr.de) from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O 3 -rich air masses from the upper troposphere -lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O 3 -rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum.

An overview of the HIBISCUS campaign

“…2 and 3, Bauru is located in an area of easterly wind north of the subtropical jet in the lower stratosphere and on the south-east side of the Bolivian upper tropospheric high in a W-SW wind regime (see Huntrieser et al, 2007). From Bauru, short-duration balloons can fly west towards accessible areas with safe payload recovery for short-duration balloons and towards the Pacific for the long-duration balloons to start their tropical circumnavigation.…”

“…radar, lidar, lightning network) provided by IPMet in the frame of a Brazilian collaborative project Tropical Convection and Cirrus Brazil (TroCCiBras) (Held et al, , 2008. There was close collaboration with the European tropical project TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment) (Huntrieser et al, 2007), with the Deutsches Zentrum für Luft-und Raumfahrt (DLR) Falcon aircraft being deployed from a nearby airport. In addition, collaboration was established with the European Space Agency giving access to the data of the Environmental Satellite (ENVISAT) measurements prior to their public release, and with the ODIN Swedish-Canada-Finish-French satellite for reinforced observations over the area during the period.…”

Evidence for heterogeneous chlorine activation in the tropical UTLS

“…2c). This is probably caused by the fact that only a subset of flights during TROCCINOX and SCOUT-O 3 were performed in tropical air masses Huntrieser et al, 2007). Cl y was initialised as a function of O 3 as described in Sect.…”

“…In February 2005, the aircraft was deployed from Araçatuba, Brazil, during the TROCCINOX campaign. Observations inside cirrus clouds were made during several flights in the altitude range 10-15 km (see Huntrieser et al, 2007, andKonopka et al, 2007, for detailed information on all flights and meteorological conditions). During the SCOUT-O 3 campaign in November/December 2005, flights were carried out from Darwin, Australia.…”

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

“…Photolytic conversion has been demonstrated to be affected by a negative interference from the photolysis products of VOCs reacting with NO within the photolysis cell (Villena et al, 2012) and has a possible positive interference from thermal decomposition of NO y (McClenny et al, 2002). Measurements of NO and NO 2 have been made in a range of low-NO x locations using the chemiluminescence technique (Huntrieser et al, 2007;Lee et al, 2009;Peterson and Honrath, 1999;Zhang et al, 2008). Measurement of NO x by the NO chemiluminescent technique in these locations can be challenging (Yang et al, 2004), often operating close to the limit of detection (LOD).…”