Temporal and spatial distribution characteristics of atmospheric pollutants in urban area of Kunming City

Based on the monitoring data of national control monitoring stations in the urban area of Kunming in 2013-2020, the temporal and spatial distribution features of atmospheric pollutants were analyzed. The results showed that during the period of 2013-2020, the annually-averaged concentration of O₃ in the urban area of Kunming generally showed an upward trend, and the annually-averaged concentrations of other pollutants showed a downward trend. The annually-averaged concentration of O₃ increased by 4.1%, while that of SO₂ dropped by 67.9% and other pollutants dropped by 35.0%-55.0%. The proportion of days of primary pollutants exceeding Level 1 or above the standard of Ambient Air Quality Standards (GB 3095—2012 ) indicated that O₃ instead of PM_2.5 had become the primary atmospheric pollutant in Kunming. The highest concentration of O₃ appeared in spring, followed by summer, and the lowest in autumn, the concentrations of PM₁₀ and PM_2.5 were generally high in spring and winter but low in autumn, and as for SO₂, NO₂ and CO, the highest concentrations appeared in winter and lowest in summer. But the variation ranges in four seasons of SO₂ and NO₂ were smaller than that of other pollutants. O₃ in spring and summer and PM_2.5 in spring and winter were the key points of air pollutants control in Kunming. The daily variation of O₃ presented single peak distribution, CO, NO₂, PM₁₀ and PM_2.5 presented double peaks distribution, but the variation of peak-valley of PM₁₀ and PM_2.5 concentrations were not distinct. The peaks of NO₂, PM_2.5, PM₁₀ and CO were identical to morning rush hours, the peak of O₃ usually appeared during 14:00-15:00, and the concentration of SO₂ was higher in the morning than in the afternoon. As for spatial distribution patterns, remarkable distinctions existed for different pollutants. The concentrations of SO₂, PM_2.5, NO₂, PM₁₀ and CO of western stations were 54.5%, 20.0%, 17.9%, 14.6% and 2.4%, respectively higher than those of eastern stations. On the contrary, O₃ concentrations in eastern stations were 9.0% higher than that of western stations. The difference of SO₂, NO₂ and O₃ concentrations between eastern and western stations had narrowed down year by year, and this might be caused by the weakening of the impact of pollution transmission from Anning Industrial Park.