We study the seasonal variations of δ13C ratios in aerosol fine particulate matter (PM2.5) using 91 PM2.5 samples collected from Xinxiang, China, during the summer and winter in 2017. Mass concentrations of total carbon (TC), water soluble ions, and stable carbon isotope ratios (δ13C) were determined. The mean concentrations of TC in the summer and winter were 11.78 μg·m-3 and 26.6 μg·m-3, respectively. The δ13C ratio in the summer ranged from -27.70‰ to -25.22‰. The daily δ13C ratio fluctuated in the first half of the summer months (mean -26.96‰), whereas the δ13C ratio in the second half of the summer was relatively stable (mean -25.69‰). The number of fires in the study area during the first half of the summer was quite different to the number during the second half of the summer, meanwhile, there was a positive correlation between the Knss+ concentration and the TC mass concentration (R2=0.62, P<0.01). This indicates that biomass burning most likely contributed to variations in δ13C. During the winter there was a significant negative correlation between winter RH and the TC/PM2.5 mass ratio (R2=0.68, P<0.01), which suggests that SOA growth was dominant in the early stage of haze development, whereas the pollution period was dominated by SIA components. The ratio of δ13C ranged from -26.72‰ to -23.49‰, and there was a difference between the variation of the δ13C ratio in haze episode (when it was mainly enriched in the development stage) to that in the stage dominated by depletion.
Keywords: PM2.5; Xinxiang City; haze episode; relative humidity; stable carbon isotope ratio.