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.

The characteristics of biogenic aerosols in an urban area were explored by determining the composition and temporal distribution of saccharides in PM_2.5 in Shanghai. The total saccharides showed a wide range of 9.4 ng/m³ to 1652.9 ng/m³, with the averaged concentrations of 133.1 ng/m³, 267.5 ng/m³, 265.1 ng/m³, and 674.4 ng/m³ in spring, summer, autumn, and winter, respectively. The saccharides include anhydrosaccharides (levoglucosan and mannosan), which were higher in cold seasons due to the increased biomass burning; saccharide alcohols (mannitol, arabitol, sorbitol); and monosaccharides (fructose, glucose), which were more abundant in warm seasons and attributed to the biological emissions. Through positive matrix factorization (PMF) analysis, four emission sources of saccharides were resolved, including biomass burning, fungal spores, plant decomposition, and pollen. Moreover, the process analysis of high concentrations of leveglucosan was conducted by backward trajectory and fire points. We found that concentrations of anhydrosaccharides were relatively stable under different pollution levels, while saccharide alcohols exhibited an obvious decrease with the concentration of PM_2.5, indicating that biomass burning was not the core reason for heavy haze pollution. However, high level PM_2.5 pollution might inhibit the effects of biological activities.

PM_2.5 pollution over Hangzhou Bay area, China has received continuous attention. In this study, PM_2.5 samples were collected simultaneously in six typical cities in Zhejiang Province from 15 October 2019 to 15 January 2020 (autumn and winter) and from 1 June to 31 August 2020 (summer), and major water-soluble ions were analyzed. Average concentrations of NO₃⁻ and SO₄²⁻ in the six cities were 3.93–15.64 μg/m³ and 4.61–7.58 μg/m³ in autumn and winter, with mass fractions of NO₃⁻ and SO₄²⁻ in PM_2.5 up to 19.6–34.2% and 13.6–26.3%, respectively, while in summer, they were 1.23–2.64 μg/m³ and 2.22–4.14 μg/m³, with mass fractions of 7.0–15.0% and 14.7~25.1%. Both NO₃⁻ and SO₄²⁻ were mostly from gas-to-particle transformation of precursors. High relative humidity in the six cities was suggested to significantly promote the formation of NO₃⁻ and SO₄²⁻, particularly in autumn and winter, while enhanced atmospheric oxidation favored the formation of SO₄²⁻ in summer. However, the formation of NO₃⁻ was inhibited under a high temperature of >15 °C. The concentrations of SO₄²⁻ and NO₃ were mostly correlated with each other among the six cities. Potential source contribution function analysis indicated that both SO₄²⁻ and NO₃⁻ were mostly from local pollution of Hangzhou Bay area in Zhejiang Province and also transported from Shanghai and the southern region of Jiangsu Province. This study contributed to the understanding of regional characteristics of SO₄²⁻ and NO₃⁻ in Hangzhou Bay area and suggested that joint prevention and control efforts should be strengthened to reduce regional PM_2.5 pollution.

By analyzing the mass concentrations and compositions of atmospheric PM_2.5 in Shaoxing from December 2019 to February 2020, the characteristics of carbon-containing components, water-soluble ions and metal elements were obtained. NO₃⁻, OC, SO₄²⁻ and NH₄⁺ were the main components of PM_2.5 in winter. The OC/EC ratio was 3.27, which proved the existence of SOC. The proportion of SOC in OC was 47.3%, which showed that secondary sources made a significant contribution. The values of OC/EC and NO₃⁻/SO₄²⁻ indicated that vehicle exhaust emissions also made a significant contribution to PM_2.5. Trace elements of Na, Ca, K and Cd had higher enrichment factor values and were enriched due to human activities. Finally, PM_2.5 sources analysis was performed by the positive matrix factorization model. The results showed that secondary inorganic salts (49.3%), motor vehicles and industrial sources (21.3%) and dust sources (17.0%) were the important sources of PM_2.5 pollution.

The characteristics of biogenic aerosols in urban area were explored by determining the composition, temporal distribution of saccharides in PM_2.5 in Shanghai. The total saccharides showed a wide range of 15.2 ng/m³ to 1752.8 ng/m³, with the averaged concentrations were 169.8 ng/m³，300.5 ng/m³，288.4 ng/m³，688 ng/m³ in spring, summer, autumn, and winter, respectively. The concerned saccharides include anhydrosaccharides (levoglucosan and mannosan), which were higher in cold seasons due to the increased biomass burning, saccharide alcohols (mannitol, arabitol, sorbitol) and monosaccharides (fructose, glucose), which showed more abundant in warm seasons attributed to the biological emissions. By PMF analysis, four emission sources of saccharides were demonstrated, including biomass burning, fungal spores, soil suspension and plant pollens. Resolution of backward trajectory and fire points showed a process of high concentrations of levoglucosan. We found that concentrations of anhydrosaccharides showed relatively stable under different pollution levels while saccharide alcohols exhibited an obvious decrease, indicated that biomass burning was not the core reason of the heavy haze pollution, however, and high level PM_2.5 pollution might inhibit effects of biological activities.