Spatiotemporal variations and relationship of PM and gaseous pollutants based on gray correlation analysis

The present work characterizes the spatiotemporal variations of air pollution at four sites in Xi'an city. The investigations lasted for 1 year: January 1 through December 31, 2015. The concentrations of CO, NO₂, O₃, PM and SO₂ were systematically monitored. The gray correlation analysis was used to correlate PM_2.5 and gaseous pollutants. The formation mechanisms of sulfate and nitrate aerosols were discussed. Results clearly revealed severe air pollution by PM_2.5, PM₁₀ and NO₂ at all four sites. Significant monthly variations were observed for PM_2.5, PM₁₀, SO₂ and CO with the maximum values in December/January and minimum values in June/July. The O₃ level showed an opposite trend. Spatially, high variations were observed for PM and some gaseous pollutants at individual sites. Gray correlation analysis revealed the significance of various major influencing factors on seasonal PM_2.5 values at each site. In general, PM₁₀, SO₂ and NO₂ affect the PM_2.5 more than other pollutants. For a more efficient control of air pollution, a systematic spatial characterization of the seasonal variability of individual influencing factors is necessary.