Objective To investigate the exposure characteristics of air pollutants in Lanzhou from 2013 to 2017, and study the exposure level of air pollution after the implementation of the "Coal to Gas" project.
Methods The daily monitoring data of main air pollutants (PM10, PM2.5, SO2, NO2, CO, and O3) in Lanzhou from 2013 to 2017 were collected, and combined with population distribution data, population-weighted exposure level (PWEL) was calculated. The exposure trend coefficient (rs) was calculated by Daniel trend test. Then ambient air quality index (AQI), composite index (Isum), and environmental pollutant exposure share rate (Pi) were used to assess ambient air pollution exposure qualitatively and quantitatively.
Results PM10 was ranked bottom in the qualified rate of daily concentration (84.2%) from 2013 to 2017, followed by PM2.5 (89.2%), while others were all above 95%. Compared with 2013, the concentrations of PM2.5, PM10, and SO2 in 2017 decreased by 35.0%, 21.6%, and 9.2%, respectively, while the concentrations of NO2, CO, and O3 in 2017 increased by 27.0%, 25.0%, and 132.3% respectively. The annual ratios of PM2.5/PM10 were between 0.40 and 0.48; while the annual ratios of NO2/SO2 were between 1.44 and 2.35, and showing a sharp increase since 2014. From 2013 to 2017, the days with AQI < 100 showed an increasing trend; in comparison with 2013, the days in 2017 increased by 21.4%, and high exposure levels were mainly concentrated in seasons of winter and spring. The Isum for each selected year was 2.68, 2.74, 2.87, 2.83, 2.73, respectively, with a median for 2013-2017 of 2.79. The Pis of PM2.5, PM10, and gaseous pollutants were in the ranges of 0.125-0.375, 0.1-0.4, and 0.3-0.7, respectively. The share of the exposure load of particulate matters showed a downward trend, while that of gaseous pollutants showed an upward trend.
Conclusion The implementation of "Coal to Gas" project has lowered the exposure to particulate matters (especially PM2.5) in Lanzhou. However, particulate matter (especially PM10) is still the main air pollution exposure in Lanzhou, and the exposure load of gaseous pollutants (especially O3) shows an increasing trend in recent years.
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