Identification of potential regional sources of ambient criteria air pollutants at a national-controlled air quality observational site in Guiyang

Comprehensively characterizing air pollutant cross-boundary transport is indispensable for determining effective control measures to further improve air quality. Taking advantage of the datasets of criteria pollutants (i.e., PM₁₀, PM_2.5, SO₂, CO, NO, NO₂, NO_x and O₃) and meteorological parameters, we comprehensively characterized the regional transport of air pollutants in Guiyang using BPPs (Bivariate polar plots), HYSPLIT 4 (Hybrid Single Particle Lagrangian Integrated Trajectory), PSCF (potential source contribution function) and CWT (concentration weighted trajectory) models. The average mass concentrations of PM₁₀, PM_2.5, SO₂, CO, NO₂ and O₃ were lower than that the CNAAQ Class I standards, and were much lower than these in the key air pollution control regions for the “Blue Sky Protection Campaign”. Decreasing trends of PM₁₀, PM_2.5, SO₂, NO, NO₂ and NO_x, and increasing trend of O₃ were observed, confirming the effectiveness of air pollution control policies, and suggesting continuous and effective emission control measures should be implemented for further improving air quality. The BPPs revealed that all pollutants, except O₃, had higher mass concentrations when wind speeds were low, and in the high wind speed scenario, the dependence of air pollutants concentrations on wind speed and wind direction was more varied seasonally. High concentration back trajectories, PSCF and CWT analysis demonstrated that both tailored local emissions reduction and regional cooperative control, which should be taken when suitable, are crucial for controlling multiple pollutants and hence further improving air quality in Guiyang in the upcoming years.