Analysis of the influencing factors and sources of brown carbon light absorption in a typical megacity of the Yangtze River Delta, China

Abstract Brown carbon (BrC) is a new term for organic aerosol (OA) with strong absorption ability from the vis to UV wavelengths, which plays a vital role in atmospheric visibility and climate change. Herein, we report field measurements from 1 March 2020 to 28 February 2021, sampled at the urban Suzhou, Yangtze River Delta (YRD), China, to investigate the optical properties and sources of BrC. The light absorption of BrC was found to be highest (babs370=9.0±7.2 Mm-1) in winter and lowest (babs370=5.1±3.3 Mm-1) in summer, respectively. The AAE value of BrC in winter was 1.22±0.05, followed by 1.21±0.05, 1.20±0.05, and 1.19±0.05 for fall, spring and summer, respectively. The MAC of secondary organic carbon (SOC) was 3.3±0.2 m2g-1 in spring, 2.9±0.1 m2g-1 in summer, 4.3±0.1 m2g-1 in fall and 2.8±0.2 m2g-1 in winter, significantly lower than that of primary organic carbon (POC) (12.1±0.3 m2g-1 in spring, 10.2±0.2 m2g-1 in summer, 13.6±0.3 m2g-1 in fall and 10.7±0.2 m2g-1 in winter) at 370nm, suggesting photochemical oxidation could weaken the light absorption of aged BrC. Five different BrC sources were identified by Positive Matrix Factorization (PMF), including a biomass burning-related, a vehicle-related, a sulfate-related, a nitrate-related, and a dust-related source, which averagely contributed 7.4%, 73.4%, 11.9%, 1.9%, and 5.4% to babs370. The Potential Source Contribution Factor (PSCF) analysis showed that high polluted period was mainly contributed by air mass from the south. Besides, the influence degree of the potential source areas, the sequence was winter > spring > fall > summer. Our results improve the understanding of BrC in an important industrial city in YRD, which could reduce the uncertainty of the prediction of its climate effect in this region.