Boundary layer perspective assessment of air pollution status in Wuhan city from 2013 to 2017

This study used daily air pollution data (PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃) from nine monitoring stations in Wuhan city to calculate the air quality index (AQI) from 2013 to 2017. Together with this data, L-band sounding data, ground meteorological data, and air mass back trajectories were also used to describe the dynamics of atmospheric boundary layer (ABL) during pollution process. Analysis of the results shows that, even though the city is still polluted, the number of polluted days was decreasing. Ranking the years in terms of pollution status shows that the year 2013 was the most polluted year while the year 2017 was the cleanest year. Average annual limit of PM₁₀, PM_2.5, and NO₂ during these 5 years were 1.3~1.8, 1.5~2.7, and 1.2~1.5 times higher than the annual average acceptable limit, respectively. The average ratio of PM_2.5/PM₁₀ for 5 years was 0.67 which signifies that a significant portion of PM_2.5 accounted for the total mass of PM₁₀. Moreover, the condition of ABL during the pollution process shows the dominance of strong ground inversion and weak to calm winds. These conditions are not favorable for horizontal and vertical mixing of air pollutants and prevent dilution of pollutants with clean air. Mean cluster analysis of air mass back trajectory shows that pollutants of local origin were more important than the trans-boundary movement of air pollutants. This indicates that the observed pollution in Wuhan was more of local origin.