Smog chamber simulation work was conducted to determine thermodynamic properties and characterize physiochemical evolution of particles under different humidity from wheat residue burning, one typical pollution source in China. The freshly emitted carbonaceous particles comprise substantial inorganic fractions up to 22% in mass, including KCl, sulfate, nitrate and ammonium. The fresh particles are hygroscopic with nonvolatile core at 250 �C, and particles over 100 nm consist of about 40% nonvolatile material by volume (evaporative temperature 250 �C), dry particle densities are mainly 1.23 � 1.30 g�cm-3, and these thermodynamic properties are distinctly different in particle size. Wheat residue burning particles show unimodal distribution mainly within accumulation mode in terms of number, surface area, and volume size. The particle size gradually grows and concentrations decrease greatly over time in the chamber. Water vapor has significant effect on particle size distribution and attenuation, major in accelerating and enhancing the particle growth and promoting concentration decrease. Particle density changes were studied and compared under high humidity and general conditions. Dry particle densities increase due to morphology, structure and chemical composition changes during aging process. The density increases from 1.266 � 0.011 to 1.324 � 0.007 g�cm-3 under general condition; while under high humidity, dry particle densities are larger and increase faster from 1.415 � 0.012 to 1.429 � 0.008 g�cm-3. Heterogeneous reactions were observed from indirect filter sampling chemical determination and TEM single particle analysis during particle evolution. Inorganic mass fraction increases from 22.44% to 23.89%, sulfate and nitrate formations contribute largely to the particulate inorganics changes, which even offset chloride loss, decreasing from 8.12% to 6.88% in mass.

Evolution of carbonaceous aerosol mixed with inorganic salts emitted from wheat straw residue burning: A smog chamber study

247th National Meeting (2014)

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