WRF-Chem model estimates of equatorial Atlantic Ocean tropospheric ozone increases via June 2006 African biomass burning ozone precursor transport

Abstract

Long-range horizontal and local vertical transport of biomass burning ozone precursors (i.e. carbon monoxide and nitrogen oxides) from Central Africa are simulated for June 2006. Twenty-kilometer resolution combined meteorological and chemical simulations examine transport pathways, spatial distribution, and quantities of ozone precursors and ozone. Results suggest that due to biomass burning, ozone mixing ratios increase by 28–33 parts per billion by volume in the lower troposphere (850 hecto-Pascals) over the Atlantic Ocean west of Central Africa during June. The inter-hemispheric transport of biomass burning emissions from Central Africa subsides over the Gulf of Guinea with a northward extent of approximately 2–5°N. In the lower troposphere, ozone mixing ratio increases decrease from 28 parts per billion by volume in the southern Gulf of Guinea to 2–3 parts per billion by volume on the Gulf of Guinea Coast. There is middle and upper tropospheric ozone enhancement of 6–12 parts per billion over the Equatorial Atlantic Ocean which is the result of convective detrainment of ozone precursors from deep convection on the Gulf of Guinea Coast followed by transport that propagates around a broad anticyclone. The model ozone produced by biomass burning emissions is less than the observed implying that lightning-induced nitrogen oxide emissions, which are not included in this simulation, are a significant tropospheric ozone source for the eastern Equatorial Atlantic Ocean.