Hourly organic carbon (OC) and elemental carbon (EC) concentrations in PM_2.5 were measured from June 2013 to May 2014 in Wanzhou, the second largest city in the Chongqing Municipality, in the southwest of China. Results show that the annual average concentrations of OC and EC were 13.16 ± 7.98 and 3.12 ± 1.51 μgC·m⁻³, respectively. Clear seasonal variations of OC and EC concentrations were observed, with their concentrations at minima in summer and maxima in winter. The diel concentration profile of OC and EC presented a bimodal pattern, which was attributed to the cooperative effects of local meteorological conditions and source emissions. The daily average OC/EC ratio ranged from 2.05 to 8.17 with an average of 4.15 for the whole study period. Strong correlations between OC and EC were found in winter and spring, indicating their common sources, while their correlations were poorer in summer and autumn, indicating that the influence of biogenic emissions and secondary organic carbon (SOC) were significant during those seasons. The estimated SOC concentrations were 2.19 ± 1.55, 7.66 ± 5.89, 5.79 ± 3.51, and 3.43 ± 2.26 μgC·m⁻³, accounting for 29.2%, 52.7%, 27.4%, and 30.5% of total organic carbon in summer, autumn, winter, and spring, respectively. The analysis of back trajectories suggested that high PM_2.5, OC, and EC concentrations were associated with air masses originating from or passing over several industrial centers and urban areas in western and northwestern China. Air trajectories from the southeast with short pathways were the dominant trajectories arriving at Wanzhou, indicating that local sources had a big influence on PM_2.5, OC, and EC concentrations.

In order to explore the characteristics of water-soluble inorganic ions (WSIIs) in the atmosphere of Wanzhou, a small mountainous city in Chongqing, four representative seasonal PM_2.5 samples and gaseous precursors (SO₂ and NO₂) were collected from April 2016 to January 2017. The WSIIs (including Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) were analyzed by ion chromatography. During the sampling period, daily PM_2.5 concentration varied from 3.47 to 156.30 μg·m⁻³, with an average value of 33.38 μg·m⁻³, which was lower than the second-level annual limit of NAAQS-China. WSIIs accounted for 55.6% of PM_2.5, and 83.1% of them were secondary inorganic ions (SNA, including SO₄²⁻, NO₃⁻, and NH₄⁺). The seasonal variations of PM_2.5 and WSIIs were similar, with the minimum in summer and the maximum in winter. PM_2.5 samples were the most alkaline in summer, weakly alkaline in spring and winter, and close to neutral in fall. The annual average ratio of NO₃⁻/SO₄²⁻ was 0.54, indicating predominant stationary sources for SNA in Wanzhou. NO₃⁻, SO₄²⁻, and NH₄⁺ mainly existed in the form of (NH₄)₂SO₄ and NH₄NO₃. The results of the principal component analysis (PCA) showed that the major sources of WSIIs in Wanzhou were the mixture of secondary inorganic aerosols, coal combustion, automobile exhaust (49.53%), dust (23.16%), and agriculture activities (9.68%). The results of the backward trajectory analysis showed that aerosol pollution in Wanzhou was mainly caused by local emissions. The enhanced formation of SNA through homogeneous and heterogeneous reactions contributed to the winter PM_2.5 pollution event in Wanzhou.

Daily PM2.5 samples were collected in the four consecutive seasons in 2013 in Wanzhou, the second largest city in Chongqing Municipality of China and in the hinterland of the Three Gorges Reservior on Yangtze River and analyzed for the mass concentrations and carbonaceous species of PM2.5 to investigate the abundance and seasonal characteristics of PM2.5, and organic carbon (OC) and elemental carbon (EC). The annual average PM2.5 concentrations were 125.3 μg·m⁻³, while OC and EC were 23.6 μg·m⁻³ and 8.7 μg·m⁻³, respectively. The total carbonaceous aerosol (TCA) accounted for 32.6% of the PM2.5 mass. On seasonal average, the OC and EC concentrations ranked in the order of winter > fall > spring > summer, which could be attributed to the combined effects of changes in local emissions and seasonal meteorological conditions. Strong OC-EC correlations were found in the winter and fall, suggesting the contributions of similar sources. The lowest OC-EC correlation occurred in the summer, probably due to the increases in biogenic emission and formation of secondary organic aerosol (SOA) through photochemical activity. Average secondary organic carbon (SOC) concentration was 9.0 μg·m⁻³, accounting for 32.3% of the total OC. The average ratios of SOA/PM2.5 of 3.8%~15.7% indicated that SOA was a minor fraction in fine particles of Wanzhou.

In this study, we quantified the atmospheric wet deposition (AWD) of 13 trace metals (TMs) and estimated their potential effects on the surface water of the Three Gorges Reservoir in China. Precipitation was collected in Wanzhou in southwestern China from March 2015 to February 2016. The concentrations and fluxes of the 13 TMs were in the ranges of 0.16–9.44 µg L⁻¹ and 0.18–10.22 mg m⁻² yr⁻¹, respectively, in the order Al > Zn > Fe > Ba > Pb > Mn > Ti > Cd > Cu > As > V > Ni ≈ Cr. Using principal component analysis, it was found that Al, Ba, Cu, Fe, Mn and Zn were mainly derived from a mixture of soil and road dust, As, Cd, Cr, Pb and Ti primarily originated from the local industries, and Ni and V were related to diesel and gasoline combustion, including both vehicle exhaust emissions and ship emissions from the nearby Yangtze River. The estimated TM inputs to the Three Gorges Reservoir were 11.1, 11.0, 5.7, 5.3, 4.5, 2.7, 2.5, 1.5, 1.0, 0.7, 0.5, 0.2, and 0.2 t yr⁻¹ for Al, Zn, Fe, Ba, Pb, Mn, Ti, Cd, Cu, As, V, Ni and Cr, respectively. The AWD TM fluxes in Wanzhou were lower than those in metropolises and their inputs were limited for surface water of the Three Gorges Reservoir. However, Cd was strongly enriched in precipitation and rainstorms greatly increased the surface water concentrations of Cd and Pb. Therefore, the behavior of Cd and Pb in southwestern mountain areas of China, including emission, transport, transformation, and their ecological effects, should be given more attention in future studies.

Organic carbon (OC) and elemental carbon (EC) concentrations were measured in daily PM_2.5 samples collected over four non-consecutive months representing four seasons from 2016 to 2017 in a small city in the east of Sichuan Basin. The average concentrations of OC and EC during the study periods were observed to be 15.5 ± 13.5 and 5.2 ± 4.7 μg∙m⁻³, respectively, both with the highest in winter. The OC and EC correlated well in fall and winter, implying that OC and EC were attributed to common emission sources. The estimated secondary OC (SOC) represented 37.2%, 46.7%, 26.9%, and 40.7% of the OC in spring, summer, fall, and winter, respectively. The highest concentration of SOC was found in winter, while the proportion of SOC/OC was highest in summer. Strong correlations were observed between OC vs. K⁺ and EC vs. K⁺ in fall and winter, suggesting that biomass burning was a significant source of carbonaceous aerosols. Four sources of OC and EC were resolved by the positive matrix factorization (PMF) model, including coal combustion (5.5% and 12.1%), building and road dust (19.7% and 18.1%), biomass burning (38.7% and 33.1%), and vehicle emission (36.1% and 36.7%), respectively. The potential source contribution function (PSCF) analysis signified that the main source areas of OC and EC were distributed in or nearby Wanzhou.

The accumulation of heavy metals (HMs) in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) area is potentially harmful to the water environment. In order to reveal whether nitrogen (N) deposition is a potential driving factor for the migration and transformation of HMs (Cd, Cr, Cu, Ni, and Pb), a simulated N deposition experiment was performed on the soil in the WFLZ of the TGR. The results showed that the accumulative release amounts of HMs increased with the increase of N deposition. It was found that the Elovich equation, double-constant equation, and parabolic diffusion equation could well describe the release process of Cu, Cd, Cr, and Ni, while the double-constant equation, parabolic diffusion equation, and first-order equation could be applicable for Pb. The exchangeable fractions of HMs increased to varying degrees after the N deposition treatment, wherein Ni was most significant, indicating that N deposition could increase the ecological risk of HM pollution in the TGR area. The results provide insight into the major factors affecting the release of different HMs under N deposition in this vulnerable region ecologically.