The Evolution of the Wave-One Ozone Maximum During the 2017 LASIC Field Campaign at Ascension Island

Aerosols associated with biomass burning sources in Southern Africa were the focus during the LASIC, CLARIFY, and ORACLES field intensives across the South Tropical Atlantic in August and September of 2017. During this period, we launched 20 ozonesondes to produce a high temporal resolution data set to complement the once per week regular ozonesondes to investigate episodes of elevated O₃ mixing ratios from westward moving biomass burning from Southern Africa. Vertical profiles of tropospheric ozone reveal the presence of elevated ozone mixing ratios due to biomass burning in the lower to middle troposphere during this period. The collected data show ozone mixing ratios exceeded 80 ppb between 850 and 550 hPa when the origin of air was Southern Africa (Angola and regions to east). We also find elevated O₃ mixing ratios in the 500–300 hPa layer, which could be linked to production of O₃ via lightning (LNO_X) from deep convection over Africa, which is transported into the Southern Hemisphere by the Tropical Easterly Jet (TEJ). Low-ozone mixing ratios in the lower troposphere are associated with transport from the Northern Tropical Atlantic, and there is evidence of pollution from South America. Surprisingly, we find limited observations of African Easterly Jet-South (AEJ-S) in its strong phase at Ascension Island, but elevated O₃ mixing ratios are found when it does occur.