Concentration prediction and spatial origin analysis of criteria air pollutants in Shanghai

Severe air pollution events still occur frequently in Shanghai. In order to predict when Shanghai air quality satisfies the National Ambient Air Quality Standards of China (NAAQSC) and identify potential source areas of criteria air pollutants for the regional joint prevention and control of air pollution, concentration data of PM_2.5, PM₁₀, SO₂, NO₂ and O₃ were collected in 2014-2022 at fourteen monitoring sites across Shanghai and surrounding areas. A first - order rate equation with harmonic regression analysis was employed for time series analysis and concentration prediction. Decreasing concentrations were observed widely over all sites except O₃ and NO₂. It is very likely that the secondary NAAQSC standards for PM_x, and SO₂ would be met by 2025 and O₃ and NO₂ would likely become the critical pollutants that determine air quality level after 2025. Regional transport was predominant for PM_x and SO₂ pollution. A 3D - CWT multisite joint location method was developed to identify their potential source areas at different spatial resolutions. Weighting function correction was assigned via information entropy of endpoint numbers in each cell. A probabilistic parameter WI_PSA was proposed to quantify and normalize the probability that grid cells are source areas in order to achieve fourteen - site joint location, and it was comparable and compatible at different spatial resolutions. Potential source areas of PM_2.5 and PM₁₀ were similar, including Henan, Shandong, Hebei and Anhui, while origin domains of SO₂ mainly covered Henan and Hebei. In all seasons, air pollution that was transported to Shanghai (i.e., PM_x and SO₂) originated mainly from the North China Plain; the contribution of marine sources was neglectable.