Photochemistry of the African troposphere: Influence of biomass‐burning emissions

Abstract

Abstract. The relative importance of biomass-burning (pyrogenic) emissions from savannas, deforestation, agricultural waste burning, and biofuel consumption to tropospheric ozone abundance over Africa has been estimated for the year 1993, on the basis of global model calculations. We also calculated the importance of this emission source to tropospheric ozone in other regions of the world and compared it to different sources on the African regional and global scales. The estimated annual average total tropospheric ozone abundance over Africa for the reference year is 26 Tg. Pyrogenic, industrial, biogenic, and lightning emissions account for 16, 19, 12, and 27%, respectively, while stratospheric ozone input accounts for 26%. In the planetary boundary layer over Africa, the contribution by biomass burning is -24%. A large fraction of the African biomass-burning-related ozone is transported away from the continent. On a global scale, biomass burning contributes -9% to tropospheric ozone. Our model calculations suggest that Africa is the single most important region for biomass-burning-related tropospheric ozone, accounting for -35% of the global annual pyrogenic ozone enhancement of 29 Tg in 1993. IntroductionLarge-scale air pollution has traditionally been associated with anthropogenic activities in the industrialized rcgions of the world, primarily in the Northern Hemisphere. }-towever, satellite measurements of tropospheric ozone (03) have shown that in addition to distinct plumes emanating from North America, Asia, and Europe, a large amount of O3 pollution originates from tropical Africa [Fishman and Larsen, 1987;Fishman et al., 1986Fishman et al., , 1990 •Presently at University of the Witwatersrand, Johannesburg, South In this paper we report on the use of a gridded biofuelrelated trace gas emission inventory created from our studies in Africa, as partial input to a three dimensional (3-D) numerical model of atmospheric transport and chemistry (Tracer Model version 3 (TM3)). The aim is to quantitatively examine the relative influence of pyrogenic emissions on tropospheric photochemistry in Africa in particular, and globally in general, during the year 1993. Model DescriptionThe model used in this study is the Tracer Model version 3 (TM3), a 3-D atmospheric transport and chemistry model which is an updated version of TM2 described by Heimann In order to facilitate the interpretation of our model results and as a check on their numerical accuracy, we stored the tendencies by all chemical reactions, wet and dry removal processes, emissions, and transport. To reduce the output, these tendencies were stored for three vertical zones roughly representing the boundary layer, the free troposphere, and the stratosphere. Furthermore, in this study, budgets were redefined so that they are given per global region (see section 3.2.2 for the global regions used) with oceans being considered separately as a single region. For simplicity, in the budgets the troposphere is defined as the region up to 100 hPa, which in the e...

The global lightning-induced nitrogen oxides source

“…Roelofs et al (2003) estimate that 13% of upper tropospheric O 3 over the Mediterranean is caused by LNO x but also note that the model underestimates the lightning contribution to NO x concentrations . Marufu et al (2000) show that 27% of the tropospheric O 3 abundance observed over Africa is caused by LNO x , but also find that the representation of details of the O 3 distribution suffers from imperfect LNO x source modelling. Cooper et al (2006) performed an analysis of O 3 profiles from measurements over midlatitude North America during July-August 2004; using a Lagrangian air parcel dispersion model, the upper tropospheric O 3 enhancement was shown to be anti-correlated with tracers of surface emissions and positively correlated with tracers of LNO x sources.…”

“…For example, upper tropospheric lightning influence on O 3 was identified over the North Atlantic , the South tropical Atlantic and both adjacent continents (Pickering et al, 1996;Thompson et al, 2000a;Martin et al, 2002b;Peters et al, 2002), the Middle East and the Mediterranean , the tropical Pacific (Ko et al, 2003;Koike et al, 2003), the Southern Pacific (Staudt et al, 2002), over Africa (Marufu et al, 2000) and over North America (Cooper et al, 2006). NO x has been shown to be positively correlated with high O 3 concentrations in the upper troposphere in about 100 km wide plumes from continental or lightning sources departing from the South-East USA over the Atlantic .…”

“…However, it was soon noted that the high spatial and temporal variability is of large importance for good comparisons with observations data (Flatøy and Hov, 1997;Stockwell et al, 1999). Lelieveld (1995, 2000); Lelieveld and Dentener (2000); Marufu et al (2000) www.atmos-chem-phys.net/7/3823/2007/ Atmos. Chem.…”

Medium-range mid-tropospheric transport of ozone and precursors over Africa: two numerical case studies in dry and wet seasons

“…Over the Tropics, Africa is an important reservoir of ozone precursor sources allowing ozone to build up through active photochemistry exacerbated by high solar radiation. The most important sources of ozone precursors over equatorial Africa are biomass burning (Marufu et al, 2000), biogenic (Jaeglé et al, 2005) and lightning (Schumann and Huntrieser, 2007). These sources present a strong regional seasonality.…”

“…These emissions account for half of the global carbon monoxide (CO) emissions (Andreae, 1993). Furthermore according to Marufu et al (2000) pyrogenic emissions account for 16% of the ozone burden over Africa through burning of different land types (mostly savannas, forest and agricultural wastes) in the northern hemisphere from November to March and in the southern hemisphere from May to October. The dynamic processes allow redistribution of such emissions on a more global scale.…”