To understand the characteristics and sources of carbonaceous aerosols,one-year PM_(2.5) samples were analyzed for their organic carbon( OC) and elemental carbon( EC) content,following the thermal/optical transmission protocol in three cities [Deyang( DY),Chengdu( CD),and Meishan( MS) ]in the Chengdu Plain.The observed annual average concentrations( μg·m∼(-3)) were in the following order: MS( 15. 8 ± 9. 6 OC and 6. 6 ± 5. 3 EC) > CD( 13. 0 ± 7. 5 OC and 4. 7 ± 3. 6 EC) > DY( 9. 6 ± 6. 1 OC and 3. 4± 2. 6 EC).Organic matter( 1. 6 OC) and EC was regarded as the total carbonaceous aerosols( TCA) amount,and the TCA/PM_(2.5) ratios at the three above-mentioned cities were 36%,34%,and 30% resp.The EC-trace method was used to estimate secondary organic carbon( SOC),which accounted for 38%,46%,and 47% of total OC in MS,CD,and DY.Daily variations of OC and EC concentrations exhibited significant daily variations,with simultaneous peaks on Oct. 12 th to 13 th,2013,Dec. 2 ndto 7 th,2013,and mid-to-late Jan.,2014.The surging concentrations of K+during the pollution period implied the contribution of biomass burning to heavy pollution.Six sources were resolved by the pos. matrix factorization( PMF) model,whose contributions to the total carbon( TC) were: biomass burning( 46%-56%),secondary aerosols( 26%-38%),vehicle emission( 9%-12%),fugitive dust( 3%-4%),coal combustion( 2%-3%),and industry emission( 1%-2%).Biomass burning activities presented a significant influence on TC throughout the year,especially in autumn and winter.