Can't See Everything Clear in Sunny Days? Thirty-Years‘ Research Shows It Is Not Only Because of Frog And Haze!Apr. 26,2016
Air pollution leads to obvious reduction of atmospheric visibility around the world. In urban area with intensive human activities, the visibility is mainly affected by the increasing of sulfate, nitrate, elemental carbon and other PM components. From 1973 to 2007, atmospheric visibility in clear days of global mainland basically showed downtrend], and the visibility in Chinese main cities showed obvious downtrend. In recent 30 years, large-scale adjustment of energy structure has made atmospheric pollution characteristics changed radically in Beijing. Coal smoke type gradually changes into motor vehicle type as well as synthesizing type.
Since the 1950s, the aerosol extinction coefficient has been in a changing process of down–up–down in Beijing. From the 1950s to the beginning of 1960s, aerosol extinction coefficient in Beijing reduced and rose gradually thereafter, and had been in downtrend since the 1990s. There was significantly positive correlation between aerosol extinction effect and atmospheric humidity in Beijing; in earlier stage, total sunshine hours was basically consistent with the varying pattern of aerosol extinction effect; in later stage, it also showed a downtrend due to the effect of the drop of the whole visibility in North China plain. In recent 10 years, the weakening of urban atmospheric flow field and the enhancing of heat island index have not strengthened aerosol extinction effect, which should be attributed to the highly effective urban atmospheric pollution control.
Seasonal variation of Beijing aerosol extinction effect has been changed from ‘high in winter and low in summer’ in 1970s into ‘low in winter and high in summer’ nowadays, which corresponds to the transition on atmospheric pollution from coal smoke type to integrated type. Seasonal variation amplitude of aerosol extinction effect gradually reduces from the north to the south in Beijing, being northern mountain area, northern plain area, urban area and southern plain area in descending order.
Yearly and diurnal variations of aerosol extinction effect showed double peaks and double valleys in Beijing. Double peaks were formed at 09:00 and 21:00, and double valleys were formed at 06:00 and 16:00. This mainly depended on the variation of PM concentration, and meanwhile it was also affected by atmospheric humidity.
Aerosol extinction effect in Beijing showed significant positive correlation with PM2.5 concentration, and was greatly affected by humidity. According to monitoring results of 2010, when RH was lower than 70%, aerosol extinction coefficient in Beijing had linear relation with PM2.5 concentration, and the coefficient was confirmed to be R2 = 0.611. Aerosol extinction effect would be enhanced significantly along with the rising of PM2.5 concentration. When the RH was higher than 70%, the response of aerosol extinction effect was not obvious against the variation of PM2.5 concentration, most of which were maintained above 0.5 km–1, and the average value of which was 1.48 km–1.
The research findings are published in the 5th issue of China Environmental Science, 2015. The bilingual version has been launched already.