Insight into the contributions of primary emissions of sulfate, nitrate, and ammonium from residential solid fuels to ambient PM2.5

Abstract

Understanding the primary emissions of sulfate (SO₄^2-), nitrate (NO₃^-), and ammonium (NH₄⁺) (SNA) from solid fuels (coal and biomass) combustion is important to study their roles in haze formation and particle growth. In this study, direct emissions of SNA and other inorganic ions (including Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cl^-) in fine particulate matter (PM_2.5) from residential coal combustion (RCC) and biomass burning (BB) were quantified through combustion chamber experiments. Emission factors (EFs) of the total quantified ions for the five types of solid fuels are in the range of 178-3,880 mg/kg, accounting for 5.8%-41.1% of the emitted PM_2.5 mass. The average proportions of SO₄^2-, NO₃^-, and NH₄⁺ in PM_2.5 emitted from RCC are 3.7%, 0.9%, and 1.0%, respectively, in comparison to 1.3%, 0.8%, and 0.1%, respectively, for BB. Despite the variations of SNA proportions seen among the solid fuel types, SO₄^2- is the most dominating inorganic ion, consistent with the emission profiles shown in other literatures. Similar mass fraction and its range of SO₄^2- are found between RCC and ambient in the northern cities, implying that the primary emission from RCC is a significant source contributor to atmospheric SO₄^2-, particularly in wintertime. According to the EFs and mass fractions of SNA determined for the solid fuels, the contribution of secondary formation to atmospheric SO₄^2- should be overestimated in ambient PM_2.5 source apportionment.