[Seasonal Variations and Source Apportionment of Carbonaceous Components in Luoyang: Implication for Brown Carbon...

A total of 98 samples were collected to analyze the seasonal variation and source apportionment of carbonaceous components, especially brown carbon (BrC), of PM_2.5in Luoyang during 2018-2019. The concentrations of organic carbon (OC) and elemental carbon (EC) ranged from (7.04±1.82) μg·m^-3to(23.81±8.68) μg·m^-3and (2.96±1.4) μg·m^-3to (13.41±7.91) μg·m^-3, respectively, showing the seasonal variation of being high in winter and low in summer; the carbonaceous fraction and secondary organic aerosol percentages were higher by 8.33%-141.03% and by 0.77%-63.14%, respectively, compared with that in 2015. The light absorption cross section (MAC) values showed different seasonal variations with the concentration of carbonaceous fraction, shown in descending order as autumn (7.67 m²·g^-1)>winter (5.65 m²·g^-1)>spring (5.13 m²·g^-1)>summer (3.84 m²·g^-1). The MAC values ranged from 3.84 to 7.67 m²·g^-1 at 445 nm, which was lower than that in coal ash. Seasonal variation in light absorption and the contribution of BrC to total light absorption (b_{abs,BrC,405 nm}, b_{abs,BrC,405 nm}/b_{abs,405 nm}) in descending order was winter (31.57 Mm^-1, 33%), autumn (11.40 Mm^-1, 25%), spring (4.88 Mm^-1, 23%), and summer (2.12 Mm^-1, 21%). The proportion of carbonaceous components decreased as haze episodes evolved, whereas the contribution of light absorption of BrC increased, highlighting the important contribution of BrC to the total light absorption. The results of PMF and correlation coefficients of b_{abs,BrC,405 nm} and PM_2.5 components indicated that motor vehicles and secondary nitrate contributed 27.7% and 24.0%, respectively. Our findings have significant scientific implications for the deep controlling of carbonaceous aerosol, especially for BrC, in Luoyang in the future.