Characterization and sources of winter PM2.5 organic and elemental carbon in the high-altitude region of Qinling Mountains

Abstract

This study represents the first investigation into the pollution characteristics and sources of atmospheric carbonaceous aerosols in the high-altitude region of Taibai Mountain in the Qinling Mountains during the winter season. Atmospheric particulate matter (PM_2.5) samples were collected from December 2019 to February 2020. The OC/EC ratio, principal component analysis, and backward trajectory analysis were employed to characterize the composition and potential sources of carbonaceous components in PM_2.5. The results showed that during the winter sampling period, the average mass concentrations of PM_2.5, OC, and EC were 49.20 ± 27.73 μg/m³, 9.88 ± 3.68 μg/m³, and 2.01 ± 1.04 μg/m³, respectively. OC and EC accounted for 20.1% and 4.1% of PM_2.5, with an OC/EC ratio ranging from 2.98 to 9.94 and an average of 5.47, indicating a significant contribution from secondary organic carbon (SOC). The average SOC concentration was 3.88 ± 1.65 μg/m³, contributing 42% of OC and 7.9% of PM_2.5. Under varying air quality conditions, OC concentrations increased with pollution levels, whereas EC concentrations initially increased and then declined. The temporal variations of OC and EC closely followed those of PM_2.5, suggesting relatively stable local emission sources during the sampling period. A combination of PCA, backward trajectory, PSCF, and CWT analyses identified road dust, coal combustion, vehicle emissions, and industrial pollution as the dominant sources of carbonaceous aerosols. The PSCF and CWT results further revealed distinct spatial and seasonal variation in source regions. From December 2019 to January 2020, major contributions originated from the Guanzhong Plain (e.g., Xi’an, Xianyang, Baoji) and southern North China (southern Shanxi, northern Henan), where winter heating-related coal combustion and industrial emissions dominated. By February 2020, the high-contribution regions shifted southwestward to the northern Sichuan Basin and southern Shaanxi, reflecting seasonal changes in atmospheric circulation. The study demonstrates that both long-range transport and local emissions significantly influence wintertime carbonaceous aerosol levels in the high-altitude Qinling Mountains. These findings underscore the importance of incorporating seasonal transport dynamics in formulating cross-regional air pollution control strategies.