Measurement report: Chemical characteristics of PM_2.5 during typical biomass burning season at an agricultural site of the North China Plain

Abstract. Biomass burning (BB) activities are ubiquitous in China, especially in North China, where there is an enormous rural population and winter heating custom. BB tracers (i.e., levoglucosan (LG), mannosan (MN) and potassium (K⁺)), as well as other chemical components were quantified at a rural site (Gucheng, GC) in North China from 15 October to 30 November, during a transition heating season, when the field burning of agricultural residues was becoming intense. The measured daily average concentrations of LG, MN and K⁺ in PM_2.5 during this study were 0.79 ± 0.75 μg m⁻³, 0.03 ± 0.03 μg m⁻³ and 1.52 ± 0.62 μg m⁻³, respectively. Carbonaceous components and BB tracers showed higher levels at nighttime than daytime, while secondary inorganic ions were enhanced during daytime. An episode with high levels of BB tracers was encountered at the end of October, 2016, with high LG at 4.37 µg m⁻³. Based on the comparison of chemical components during different BB pollution periods, it appeared that biomass combustion can obviously elevate carbonaceous components levels, whereas no essentially effect on secondary inorganic aerosols in the ambient air. Moreover, the LG/MN ratios during different BB pollution periods remained at high values (in the range of 18.3–24.9), however, the LG / K⁺ ratio was significantly elevated during the intensive BB pollution period (1.67) when air temperatures decreasing, substantially higher than in other BB periods (averaged at 0.47).