To elucidate the variations in mass concentrations of organic carbon (OC) and black carbon (BC) in PM2s and their light absorption characteristics in Lanzhou, we conducted one-year online measurements by using a newly developed total carbon analyzer (TCA08) coupled with an aethalometer (AE33) from July 2018 to July 2019. The mean OC and BC concen-trations were 6.4 +/- 4.4 and 2.0 +/- 1.3 pg/m3, respectively. Clear seasonal variations were observed for both components, with winter having the highest concentrations, followed by autumn, spring, and summer. The diurnal variations of OC and BC concentrations were sim-ilar throughout the year, with daily two peaks occurring in the morning and evening, respec-tively. A relatively low OC/BC ratio (3.3 +/- 1.2, n = 345) were observed, indicating that fossil fuel combustion was the primary source of the carbonaceous components. This is further substantiated by relatively low biomass burning contribution (fbiomass: 27.1% +/- 11.3%) to BC using aethalometer based measurement though f biomass value which increased significantly in winter (41.6% +/- 5.7%). We estimated a considerable brown carbon (BrC) contribution to the total absorption coefficient (babs) at 370 nm (yearly average of 30.8% +/- 11.1%), with a win-ter maximum of 44.2% +/- 4.1% and a summer minimum of 19.2% +/- 4.2%. Calculation of the wavelength dependence of total babs revealed an annual mean AAE370-520 value of 4.2 +/- 0.5, with slightly higher values in spring and winter. The mass absorption cross-section of BrC also exhibited higher values in winter, with an annual mean of 5.4 +/- 1.9 m2middotg-1 , reflecting the impact of emissions from increased biomass burning on BrC concentrations.(c) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

来源平台：JOURNAL OF ENVIRONMENTAL SCIENCES