Ambient measurements of light-absorption by agricultural waste burning organic aerosols

Absorption properties (absorption Ångstrom exponent and mass absorption efficiency) of agricultural waste burning organic aerosols (AWB-OA) and their impact on total absorption were investigated in Cairo (Egypt) during the post-harvest rice straw burning autumn season. At 370 nm, AWB-OA were found to account for more than 25% of total absorption on average for the period of study (and for ∼50% during intense biomass burning events), pointing out the major role potentially played by such particles on light absorption at short wavelengths. The absorption exponent obtained for AWB-OA (∼3.5) is consistent with values previously reported for biomass burning brown carbon. In addition, AWB-OA were found to exhibit high mass absorption efficiencies at the near ultraviolet/mid-visible regions (e.g. 3.2±1.6 m2 g−1 at 370 nm and 0.8±0.4 m2 g−1 at 520 nm). Such findings clearly illustrate the need to take light absorption by organic aerosols into account for a better estimate of the radiative impact of biomass burning aerosols.