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This study evaluated the interannual variations in the sources, source-specific metals, and health risks of PM2.5-bound heavy metals (HMs) based on observational data in heating seasons from 2020 to 2022 in Wangdu County, aiming to assess the impact of "coal-to-gas" (CTG) policy on air quality at rural areas. The CTG policy continued to play a positive role, both PM2.5 and 16HMs (Cr, Pb, Tl, Ba, Sb, Sn, Cd, Sr, As, Zn, Cu, Ni, Co, Fe, Mn, and V) showed a declining trend year by year with annual average reductions of 30.4% and 43.4%, respectively. Positive Matrix Factorization (PMF) model was used to analyze the sources of HMs and results indicated that the contribution of coal combustion (CC) decreased by an average of 11.8% annually. However, biomass burning (BB) increased year by year and leaped the largest contributor (33.7%) in the winter 2022, primarily driving by natural gas shortages and heating cost rises at rural areas. The concentrations of CC marker elements As and Pb decreased by 20.7% and 48.5% annually, and CC fractions declined by 15.6% and 13.5% per year, respectively. Similarly, the concentrations and fractions of BB marker element K increased by 20.6% and 7.4% annually. Industrial emissions (IE), vehicle emissions (VE), and fugitive dust (FD) all exhibited upward trends over the years. For health risk assessment: only As and Cr surpassed threshold of carcinogenic risks, and there were derived from CC and IE, therefore, CC and IE were identified as the main contributors to carcinogenic risks. However, individual elements did not exceed the threshold of non-carcinogenic risks, but the total carcinogenic risks persisted from 2020 to 2022. Specially, the total carcinogenic risks for children were 64%, which was much higher than 36% for adults. Together, adults only have non-carcinogenic risks in 2020, while children were always faced with non-carcinogenic risks. As a main contributor to both carcinogenic and non-carcinogenic risks for As, since the annual average contribution of CC to As emissions has dropped significantly by 15.6%, resulting in a year by year decline for carcinogenic and non-carcinogenic risks.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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