Transport of biomass burning emissions from southern Africa

Abstract

The transport of biomass burning emissions from southern Africa to the neighboring Atlantic and Indian Oceans during the dry season (May-October) of 2000 is characterized using ground, ozonesonde, and aircraft measurements of carbon monoxide (CO) and ozone (O3) in and around southern Africa, together with the GEOS-CHEM global model of tropospheric chemistry. The model shows a positive bias of ∼20% for CO and a negative bias of ∼ 10-25% for O3 at oceanic sites downwind of fire emissions. Near areas of active fire emissions the model shows a negative bias of ∼60% and ∼30% for CO and O 3, respectively, likely due to the coarse spatial (2° × 2.5°) and temporal (monthly) resolution of the model compared to that of active fires. On average, from 1994 to 2000, ∼60 Tg of carbon monoxide (CO) from biomass burning in southern Africa was transported eastward to the Indian Ocean across the latitude band 0° -60°S during the 6 months of the dry season. Over the same time period, ∼40 Tg of CO from southern African biomass burning was transported westward to the Atlantic Ocean over the latitudes 0° -20°S during the 6-month dry season, but most of that amount was transported back eastward over higher latitudes to the south (21° -60°S). Eastward transport of biomass burning emissions from southern Africa enhances CO concentrations by ∼4-13 ppbv per month over the southern subtropical Indian Ocean during the dry season, with peak enhancements in September. Carbon monoxide from southern African and South American biomass burning is seen in the model simulations as far away as Australia, contributing ∼8 ppbv and ∼ 12-15 ppbv CO, respectively, and thus explaining the ∼20-25 ppbv observed enhancement of CO over Melbourne in mid-September 2000. Copyright 2004 by the American Geophysical Union.