Continuous measurements of meteorological parameters, gaseous pollutants, particulate matters, and the major chemical species in PM_2.5 were conducted in urban Hangzhou from 1 September to 30 November 2013 to study the potential sources and formations of PM_2.5 pollution. The average PM_2.5 concentration was 69 µg·m⁻³, ~97% higher than the annual concentration limit in the national ambient air quality standards (NAAQS) of China. Relative humidity (RH) and wind speed (WS) were two important factors responsible for the increase of PM_2.5 concentration, with the highest value observed under RH of 70%–90%. PM_2.5 was in good correlation with both NO₂ and CO, but not with SO₂, and the potential source contribution function (PSCF) results displayed that local emissions were important potential sources contributing to the elevated PM_2.5 and NO₂ in Hangzhou. Thus, local vehicle emission was suggested as a major contribution to the PM_2.5 pollution. Concentrations of NO₂ and CO significantly increased in pollution episodes, while the SO₂ concentration even decreased, implying local emission rather than region transport was the major source contributing to the formation of pollution episodes. The sum of SO₄²⁻, NO₃⁻, and NH₄⁺ accounted for ~50% of PM_2.5 in mass in pollution episodes and the NO₃⁻/EC ratios were significantly elevated, revealing that the formation of secondary inorganic species, particularly NO₃⁻, was an important contributor to the PM_2.5 pollution in Hangzhou. This study highlights that controlling local pollution emissions was essential to reduce the PM_2.5 pollution in Hangzhou, and the control of vehicle emission in particular should be further promoted in the future.

Phytoremediation is an environment-friendly method for toxic elements remediation. The aim of this study was to improve the phytoremediation efficiency of Brassica juncea and the rhizosphere soil micro-ecology in cadmium (Cd) and arsenic (As) contaminated soil. A field experiment was conducted with six treatments, including a control treatment (CK), two treatments with two contents of Trichoderma harzianum (T1: 4.5 g m⁻²; T2: 9 g m⁻²), one biochar treatment (B: 750 g m⁻²), and two combined treatments of T1B and T2B. The results showed Trichoderma harzianum promoted the total chlorophyll and translocation factor of Brassica juncea, while biochar promoted plant biomass compared to CK. T2B treatment showed the best results, which significantly increased Cd accumulation by 187.49–308.92%, and As accumulation by 125.74–221.43%. As a result, the soil’s total Cd content was reduced by 19.04% to 49.64% and total As contents by 38.76% to 53.77%. The combined amendment increased the contents of soil available potassium, phosphorus, nitrogen, and organic matter. Meanwhile, both the activity of glutathione and peroxidase enzymes in plants, together with urease and sucrase enzymes in soil, were increased. Firmicutes (dominant bacterial phylum) and Ascomycota (dominant fungal phylum) showed positive and close correlation with soil nutrients and plant potentially toxic elements contents. This study demonstrated that phytoremediation assisted by biochar and Trichoderma harzianum is an effective method of soil remediation and provides a new strategy for enhancing plant remediation efficiency.