Characterization and sources of carbonaceous aerosols in southwest plateau of China: Effects of biomass burning and low oxygen concentration

Carbonaceous aerosols affect atmospheric radiation and visibility and endanger human health. Administrative border and topography have created significant research interests focused on Yunnan Province. We studied the chemical characteristics and sources of OC and EC in four Yunnan cities using manual sampling and positive definite matrix factorization (PMF). Backward trajectories, cluster analysis, potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) were used to evaluate the transport pathways and potential source of carbonaceous aerosols during spring. The impacts of the transport of Biomass burning (BB) emissions in Southeast Asia and incomplete combustion on carbonaceous aerosols were highlighted in the study. Daily PM2.5 concentration ranged from 12.00 mu g/m(3) to 91.50 mu g/m(3), with the average concentration of 34.03 +/- 13.49 mu g/m(3). OC and EC accounted for 19.85-44.94 % and 4.99-13.16 % of PM2.5. Average secondary organic carbon (SOC) concentration ranged from 0.82 mu g/m(3) similar to 6.42 mu g/m(3), exhibiting the highest secondary conversion rate in autumn. BB was identified as the largest single source of carbonaceous aerosols through PMF analysis. The results of backward trajectory showed that more than 63.68 % of air mass originated from Myanmar in spring, and Myanmar, Laos and Vietnam were identified as the major potential source areas by PSCF and CWT. Biomass plumes emitted by some Southeast Asian countries in the spring are likely to be transported to the Yunnan Province under the guidance of southwest winds, thereby affecting local carbonaceous aerosols. The proportions of OC and EC in PM2.5 of the Yunnan Plateau were found higher than those in the four plains of China (Northeast Plain, North China, Middle-Lower Yangtze, and Guanzhong Plain). Incomplete combustion caused by low oxygen concentrations at high altitudes was considered as the cause.