Trends in ambient air pollution levels and PM_2.5 chemical compositions in four Chinese cities from 1995 to 2017.

An in-depth analysis of the specific evolution of air pollution in a given city can provide a better understanding of the chronic effects of air pollution on human health. In this study, we reported trends in ambient concentrations of particulate matter (PM) and gaseous pollutants [sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and ozone (O₃)] from 1995 to 2017 and PM_2.5 composition for the period of 2000-2017 in Guangzhou, Wuhan, Chongqing, and Lanzhou. We provided socio-economic indicators to help explain the pollution trends. SO₂ and PM (including PM₁₀ and PM_2.5) concentrations showed a downward trend in recent years with the most notable reduction in SO₂ in Chongqing and PM_2.5 in Guangzhou. There was an overall flat trend for NO₂, while O₃ showed an upward trend in recent years except in Lanzhou. The majority of PM_2.5 mass was SO₄^2- (6.0-30 µg/m³) and organic carbon (6.0-38 µg/m³), followed by NO₃^- (2.0-12 µg/m³), elemental carbon (2.1-12 µg/m³), NH₄⁺ (1.0-10 µg/m³), K⁺ (0.2-2.0 µg/m³), and Cl^- (0.2-1.9 µg/m³). Except for secondary inorganic aerosols in Wuhan, annual average concentrations of all PM_2.5 constituents showed a declining trend after 2013, corresponding to the trend of PM_2.5. The secondary sources in PM_2.5 were found to be most prominent in Wuhan, while the most abundant EC and Cl^- in Lanzhou was attributed to the use of coal. Despite temporal and spatial variabilities across the four cities, coal combustion, traffic emissions, and secondary pollution have been the major sources of PM_2.5 pollution. These trends in ambient air pollution levels and PM_2.5 composition may help understand changes in health outcomes measured at different times within the time period of 1995-2017 in the four cities.

Duke Scholars

Author Junfeng Zhang Environmental Sciences and Policy