Impact of regionally transported biomass burning on carbonaceous aerosol characterization, contribution and degradation in Pu'er, Southwest China

Biomass burning (BB) emits carbonaceous aerosols that significantly influence air quality in Southwest China during spring. To further understand the characteristics of spring BB and its original contribution to organic carbon (OC), daily fine particulate matter (PM2.5 ) samples were collected from March to May 2022 in Pu'er, Southwest China. The concentrations of OC, elemental carbon (EC), levoglucosan (Lev), and potassium from BB (K+ BB ) during the study period ranged from 5.3 to 31.2 pg/m3 , 0.86-13.1 pg/m3 , 0.06-0.82 pg/m3 , and 0.05-2.88 pg/m3 , respectively. To eliminate the effects of Lev degradation, this study uses the Aging of Air Mass (AAM) index to correct the atmospheric concentration of Lev and combines Bayesian mixture modeling with a molecular tracer method to assess the original contribution of BB to OC. The results indicated that the AAM index was 0.18 +/- 0.05, indicating that the degradation of Lev reached 82 %. When considering the degradation of levoglucosan in the atmosphere, the primary source of BB aerosols was crop-straw combustion (71.1 %), followed by the combustion of certain hardwoods and softwoods (24.9%) and grasses (4.0 %). The original contribution of BB to OC was 62.4 %, which was much greater than the contribution when levoglucosan degradation (23.7 %) was ignored. The air mass inverse trajectories and Moderate Resolution Imaging Spectroradiometer (MODIS) fire hotspots indicated that the