Abstract:
In this study, we investigated six air pollutants from 21 monitoring stations scattered
throughout Wuhan city by analyzing meteorological variables in the atmospheric boundary
layer (ABL) and air mass backward trajectories from HYSPLIT during the pollution events.
Together with this, ground meteorological variables were also used throughout the investigation
period: 1 December 2015 to 30 November 2016. Analysis results during this period show that the city
was polluted in winter by PM2.5 (particulate matter with aerodynamics of less than 2.5 microns) and in
summer by ozone (O3). The most polluted day during the investigation period was 25 December 2015
with an air quality index (AQI) of 330 which indicates ‘severe pollution’, while the cleanest day was 26
August 2016 with an AQI of 27 indicating ‘excellent’ air quality. The average concentration of PM2.5
(O3) on the most polluted day was 265.04 (135.82) g/m3 and 9.10 (86.40) g/m3 on the cleanest day.
Moreover, the percentage of days which exceeded the daily average limit of NO2, PM10, PM2.5, and
O3 for the whole year was 2.46%, 14.48%, 23.50%, and 39.07%, respectively, while SO2 and CO were
found to be below the set daily limit. The analysis of ABL during PM2.5 pollution events showed
the existence of a strong inversion layer, low relative humidity, and calm wind. These observed
conditions are not favorable for horizontal and vertical dispersion of air pollutants and therefore
result in pollutant accumulation. Likewise, ozone pollution events were accompanied by extended
sunshine hours, high temperature, a calm wind, a strongly suspended inversion layer, and zero
recorded rainfall. These general characteristics are favorable for photochemical production of ozone
and accumulation of pollutants. Apart from the conditions of ABL, the results from backward
trajectories suggest trans-boundary movement of air masses to be one of the important factors which
determines the air quality ofWuhan.
