Abstract
Abstract. Impacts on tropospheric composition in the tropics and the Southern Hemisphere from biomass burning and other emission sources are studied using a global chemical transport model, surface measurements and satellite retrievals. Seasonal variations in observed CO at remote island sites are examined. Easter Island (eastern Pacific Ocean) is impacted indirectly by the hemispheric zonal transport of CO due to the burning in southern Africa/South America, via the westerlies. An increasing trend in CO by 0.33 ppb yr−1 in the past decade at Ascension Island is attributed to the combined effects of South American/southern Africa burnings and the increases in CH4 level. Compared to Easter Island and Ascension Island, much less contribution from biomass burning to atmospheric CO is found at the island of Mahé (western Indian Ocean), where the total CO peaks in January–February, reflecting the contributions of anthropogenic emissions from India. We also examine the 2000–2050 changes in atmospheric composition in the tropics and the Southern Hemisphere driven by future changes in emissions and climate. Changes in solar radiation (UV) over South Atlantic Ocean (SAO) in future January have dominant effects on the O3 distribution. More than 55% of O3 concentrations over the SAO in both present-day and future September are not directly affected by the emissions (including lightning) over the adjacent two continents but are attributable to the transport of O3 from surrounding areas due to CO and CH4 oxidation and stratospheric intrusion. High NOx emissions in both continents in 2050s increase PAN concentrations over remote oceans at the higher southern latitudes (> 35° S) as far as those near Australia, affecting the O3 budget over there. Future changes in biomass burning and anthropogenic NOx emissions in southern Africa lead to a new area of high O3 concentrations near South Africa. The resulted O3 outflow to the Indian Ocean is pronounced due to the effects of the persistent anticyclone. A general reduction in future OH radical concentrations is predicted over the remote marine boundary layer in the tropics and the Southern Hemisphere, as a result of the increases in CH4 and CO emissions.
Highlights
Emissions from biomass burning are an important source for a number of atmospheric trace gases including carbon monoxide (CO), nitrogen oxide (NOx), ozone (O3), and aerosols, including black carbon
In the 2050s, PAN concentrations in the lower troposphere are enhanced by the increases in NOx emissions from both continents and reach 0.07 ppb over remote oceans in the higher latitudes (> 35◦ S) far away from the continents to the regions near Australia, despite higher future temperatures reducing the potential of long-range transport (LRT) of PAN (Wu et al, 2008a)
In 2050s, lower tropospheric CO concentrations of up to 500 ppb are simulated over Africa in January, which are mainly caused by increases in biomass burning emissions
Summary
Emissions from biomass burning are an important source for a number of atmospheric trace gases including carbon monoxide (CO), nitrogen oxide (NOx), ozone (O3), and aerosols, including black carbon. Biomass burning accounts for about 30 % of the global total CO source (Galanter et al, 2000). These trace gases and aerosols play important roles in tropospheric chemistry, air quality and global climate (Levine et al, 1995; Granier et al, 2000; Haywood et al, 2008). They can affect the abundance of hydroxyl radical (OH), which is the major oxidizing agent in the troposphere. In particular the campaign of Transport and Atmospheric
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