Particulate Matter and Gaseous Pollutions in Three Metropolises along the Chinese Yangtze River: Situation and...

The situation of criteria atmospheric pollutants, including particulate matter and trace gases (SO₂, NO₂, CO and O₃), over three metropolises (Chongqing, Wuhan, and Nanjing), representing the upstream, midstream and downstream portions of the Yangtze River Basin from September 2015 to August 2016 were analyzed. The maximum annual mean PM_2.5 and PM₁₀ concentrations were 61.3 and 102.7 μg/m³ in Wuhan, while highest annual average gaseous pollutions occurred in Nanjing, with 49.6 and 22.9 ppb for 8 h O₃ and NO₂, respectively. Compared to a few years ago, SO₂ and CO mass concentrations have dropped to well below the qualification standards, and the O₃ and NO₂ concentrations basically meet the requirements though occasionally is still high. In contrary, about 13%, 25%, 22% for PM_2.5, and 4%, 17%, 15% for PM₁₀ exceed the Chinese Ambient Air Quality Standard (CAAQS) Grade II. Particulate matter, especially PM_2.5, is the most frequent major pollutant to poor air quality with 73%, 64% and 88% accounting for substandard days. Mean PM_2.5 concentrations on PM_2.5 episode days are 2⁻3 times greater than non-episode days. On the basis of calculation of PM_2.5/PM₁₀ and PM_2.5/CO ratios, the enhanced particulate matter pollution on episode days is closely related to secondary aerosol production. Except for O₃, the remaining five pollutants exhibit analogous seasonal patterns, with the highest magnitude in winter and lowest in summer. The results of back trajectories show that air pollution displays synergistic effects on local emissions and long range transport. O₃ commonly demonstrated negative correlations with other pollutants, especially during winter, while moderate to strong positive correlation between particulate matter and NO₂, SO₂, CO were seen. Compared to pollutant substandard ratios over three megacities in eastern China (Beijing, Shanghai, and Guangzhou), the situation in our studied second-tier cities are also severe. The results in this paper provide basic knowledge for pollution status of three cities along Chinese Yangtze River and are conductive to mitigating future negative air quality levels.