Concentrations and light absorption properties of PM2.5 organic and black carbon based on online measurements in Lanzhou, China

• Published in: Journal of environmental sciences (China) 2023-09, Vol.131, p.84-95
• Main Authors: Chen, Pengfei, Kang, Shichang, Gan, Qinyi, Yu, Ye, Yuan, Xianlei, Liu, Yajun, Tripathee, Lekhendra, Wang, Xiaoxiang, Li, Chaoliu
• Format: Article
• Language: English
• Subjects: Black carbon; Brown carbon; Lanzhou; Light absorption; Source
• ISSN: 1001-0742; 1878-7320
• DOI: 10.1016/j.jes.2022.08.007

•Online OC and BC were measured by a newly developed TCA08 coupled with an AE33.•The annual average fbiomass to BC was 27.1% but in winter it increased to 41.6%.•BrC contribute 30.8% to total absorption coefficient with winter maximum of 44.2%.•High AAE370-520 and MACBrC, 370 in winter suggest more impact from biomass burning. To elucidate the variations in mass concentrations of organic carbon (OC) and black carbon (BC) in PM2.5 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 concentrations were 6.4 ± 4.4 and 2.0 ± 1.3 µg/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 similar throughout the year, with daily two peaks occurring in the morning and evening, respectively. 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 fbiomass 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 winter 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 m2/g, reflecting the impact of emissions from increased biomass burning on BrC concentrations.