Dynamic response of light absorption by PM2.5 bound water-soluble organic carbon to heterogeneous oxidation

Figures & data

Figure 1. Schematic diagram of the (a) setup for collecting ${\mathrm{PM}}_{2.5}$ from rice-straw smoldering smoke inside a fume-hood and (b) collected ${\mathrm{PM}}_{2.5}$ on 47 mm QMA filter paper. The detail of the setup is given in subsection 2.1.

Figure 2. Changes in light absorptivity of water-soluble organic-carbon (WSOC) from rice straw smoldering due to heterogeneous photochemical aging. (a) Absorption spectra of fresh and irradiated WSOC. Wavelength dependent mass absorption coefficients (MAC) are plotted along the y-axis and corresponding wavelengths are plotted along the x-axis. The inset summarizes the absorption Ångström exponents (AAE) and OC mass concentrations ($c_{\mathrm{OC}}$) of the fresh and each of the irradiated samples. The AAE values were calculated by using Equation (4)(4) $$\mathrm{AAE}=-\frac{\ln \left(\frac{{\mathrm{MAC}}_{{\lambda }_1}}{{\mathrm{MAC}}_{{\lambda }_2}}\right)}{\ln \left(\frac{{\lambda }_1}{{\lambda }_2}\right)}$$(4) . (b) Linear fits of lnMAC(λ) in the 280–400 nm and 400–500 nm intervals and at 365 nm are plotted against corresponding irradiation times to determine the photo-bleaching rate constant. Error bars represent standard deviations of three individual experimental values.

Figure 3. Wavelength dependent variation of the relative quantum efficiency (${\mathrm{Ф}}_{\mathrm{WSOC}}$, in the y-axis) of the water-soluble organics in ${\mathrm{PM}}_{2.5}$ from rice-straw smoldering smoke. The ${\mathrm{Ф}}_{\mathrm{WSOC}}$ values were calculated using Equation (6)(6) $${\mathrm{Ф}}_{\mathrm{WSOC}}={\mathrm{Ф}}_{2\mathrm{N}\mathrm{B}}\frac{j_{\mathrm{WSOC}}\times {ϵ}_{2\mathrm{N}\mathrm{B}}}{j_{2\mathrm{N}\mathrm{B}}\times {ϵ}_{\mathrm{WSOC}}}$$(6) and data from Figure S4. The error bars represent standard deviations calculated from three individual experiments.

Figure 4. (a) Plot of the imaginary part of refractive index (κ) along the y-axis against corresponding wavelengths along the x-axis. The downward arrows indicate the representative wavelengths of which the κ values are plotted in the inset figure; Inset: Decay of κ (in log scale) with irradiation time. Error bars represent standard deviations of three individual experimental values. (b) FTIR spectra of fresh and aged water-soluble organic-carbon.