Influence of corona discharge on the ozone budget in the tropical free troposphere: a case study of deep convection during GABRIEL
- 1Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, Mainz, Germany
- 2Science Division, Environment Canada, Vancouver, Canada
- 3University of Wollongong, School of Chemistry, Wollongong, Australia
- *now at: Institute for Atmospheric Physics, University Mainz, Mainz, Germany
- **now at: Oeschger Centre for Climate Change Research, Bern Switzerland; Institute of Geography, University of Bern, Bern, Switzerland
- ***now at: Institute for Reference Materials and Measurements, JRC Geel, Belgium
Abstract. Convective redistribution of ozone and its precursors between the boundary layer (BL) and the free troposphere (FT) influences photochemistry, in particular in the middle and upper troposphere (UT). We present a case study of convective transport during the GABRIEL campaign over the tropical rain forest in Suriname in October 2005. During one measurement flight the inflow and outflow regions of a cumulonimbus cloud (Cb) have been characterized. We identified a distinct layer between 9 and 11 km altitude with enhanced mixing ratios of CO, O3, HOx, acetone and acetonitrile. The elevated O3 contradicts the expectation that convective transport brings low-ozone air from the boundary layer to the outflow region. Entrainment of ozone-rich air is estimated to account for 62% (range: 33–91%) of the observed O3. Ozone is enhanced by only 5–6% by photochemical production in the outflow due to enhanced NO from lightning, based on model calculations using observations including the first reported HOx measurements over the tropical rainforest. The "excess" ozone in the outflow is most probably due to direct production by corona discharge associated with lightning. We deduce a production rate of 5.12 × 1028 molecules O3 flash−1 (range: 9.89 × 1026–9.82 × 1028 molecules O3 flash−1), which is at the upper limit of the range reported previously.