Research on air pollution characteristics and influencing factors of typical urban road traffic densified monitoring stations

Based on the requirements of the 14th Five-Year Plan (2021-2025) of ecological environment monitoring, aiming at the lack of study about air pollution characteristics and influencing factors of typical urban road traffic densified monitoring stations in China, the concentrations of six conventional air pollutants and meteorological parameters were monitored at different points and heights on both sides of typical roads in Lanzhou City, Gansu Province, where mobile sources were the main source of air pollution. Meanwhile, road traffic flow and vehicle type information were acquired to explore the characteristics and influencing factors of air pollution. The results showed that there existed differences in the concentrations of air pollutants on both sides of the road and at different locations on the same side of the road. The concentrations of PM_2.5 and PM₁₀ declined with the height of the monitoring sites increasing, peaking at 2-meter height, whereas SO₂, NO₂, CO, and O₃ showed a trend of first increasing and then decreasing with height, reaching their highest concentrations at 4-meter height. Hourly concentrations of SO₂, NO₂, PM_2.5, PM₁₀ and CO peaked at 05:00 to 09:00 and troughed at 15:00 to 17:00; while O₃ peaked and troughed at exactly the opposite time. The concentrations of NO₂ and CO were greatly affected by the traffic flow. Furthermore, NO₂ concentrations had a very strong correlation with the volume of heavy-duty trucks and CO concentrations had a strong correlation with the volume of light-duty passenger vehicles during the representative time period. During the monitoring period the daily average concentrations of the six pollutants were negatively correlated with relative humidity; the daily average concentrations of NO₂, PM_2.5, PM₁₀ and CO were negatively correlated with wind speed, while O₃ was positively correlated with wind speed.