Abstract
Abstract. Emissions from agricultural biomass burning (ABB) in northern China have a significant impact on the regional and global climate. The monthly average aerosol optical depth (AOD) at 550 nm in northern China in 2007 had a maximum of 0.7 in June. The AOD measurements are consistent with regional brown hazes that occurred at that time, which was a period of severe aerosol pollution. Aerosol particles were collected in urban Beijing from 12 to 30 June 2007, during a period of high haze, and studied using transmission electron microscopy with energy-dispersive X-ray spectrometry. The dominant particle types collected in the fine fraction (diameter <1 μm) were ammonium sulfate, soot, K2SO4, KNO3, and organic matter, except that the K salts were minor between 21 and 30 June. K-rich particles as tracers of biomass burning, together with wildfire maps, show that intense regional ABB in northern China contributed significantly to the regional haze between 12 and 20 June. We therefore grouped the episodes into type-1 and -2 haze, with the former occurring between 12 and 20 June and the latter between 21 and 30 June. After long-range transport, ABB particles in the type-1 haze exhibited marked changes in morphology, composition, and mixing state. KCl particles were absent, presumably having been converted by heterogeneous reactions to K2SO4 and KNO3. Soot particles were mixed with the other particle types. Abundant organic matter and soluble salts emitted by ABB increased their sizes during transport and resulted in more hygroscopic aerosol particles in downwind areas, becoming additional cloud condensation nuclei. The high AOD (average value 2.2) in Beijing during 12 to 20 June is partly explained by the hygroscopic growth of fine aerosol particles and by the strong absorption of internally mixed soot particles, both coming from regional ABB emissions. Therefore, it is important to consider the origins of the haze, which in turn leads to the different particle types.
Highlights
Biomass burning is a global phenomenon that releases large quantities of gases and aerosol particles that affect the atmospheric chemistry and climate by scattering and absorbing solar radiation on regional and global scales (Crutzen and Andreae, 1990)
We infer from wildfire maps (Fig. 7) that the intense Agricultural biomass burning (ABB) emissions in type-1 haze increased the loading of PM10 and SO2 in Beijing air
transmission electron microscopy (TEM)/energy-dispersive X-ray spectrometer (EDS) measurements showed that potassium salts (K2SO4 and KNO3) were abundant in fine particles collected during 12–20 June, and were minor during 21–30 June
Summary
Biomass burning is a global phenomenon that releases large quantities of gases and aerosol particles that affect the atmospheric chemistry and climate by scattering and absorbing solar radiation on regional and global scales (Crutzen and Andreae, 1990). Aerosol particles from biomass burning dramatically increase the concentration of cloud condensation nuclei (CCN) and affect the formation and lifetime of clouds (Andreae et al, 2004; Roberts et al, 2003). Such aerosol particles serving as CCN alter the radiation budget of clouds in the troposphere (IPCC, 2007). Because of the transport of biomass-burning particles with nutrient species (e.g., S, K, and N) from agricultural regions into urban areas, these aerosols alter the regional biogeochemical cycling and adversely affect human health (Bowman et al, 2009; Crutzen and Andreae, 1990; Da Rocha et al, 2005; Koe et al, 2001; Niemi et al, 2005; Reid et al, 2005). Numerous studies have shown that the mixtures of pollutants from industries, biomass burning, and urban areas in northern China can be transported over the Pacific Ocean (Jacob et al, 2003; Ma et al, 2003) into North America and cause problems across
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