Comparison and trend study on acidity and acidic buffering capacity of particulate matter in China

The acidity of about 2000 particulate matter samples from aircraft and ground-based monitoring is analyzed by the method similar to soil acidity determination. The ground-based samples were collected at about 50 urban or background sites in northern and southern China. Moreover, the acidic buffering capacity of those samples is also analyzed by the method of micro acid-base titration. Results indicate that the acidity level is lower in most northern areas than those in the south, and the acidic buffering capacity showed inverse tendency, correspondingly. This is the most important reason why the pollution of acidic-precipitation is much more serious in Southern China than that in Northern China. The acidity increases and the acidic buffering capacity drops with the decreasing of the particle sizes, indicating that fine particle is the main influencing factor of the acidification. The ionic results show that Ca salt is the main alkaline substance in particulate matter, whereas the acidification of particulate matter is due to the SO2 and NOx emitted from the fossil fuel burning. And among of them, coal burning is the main contributor of SO2, however the contribution of NOx that emitted from fuel burning of motor vehicles has increased in recent years. By comparison of the experimental results during the past 20 years, it can be concluded that the acid precipitation of particulate matter has not been well controlled, and it even shows an increasing tendency in China lately. The acid precipitation of particulate matter has begun to frequently attack in part of the northern areas. Multiple regression analysis indicates that coefficient value of the ions is the lowest at the urban sites and the highest at the regional sites, whereas the aircraft measurement results are intermediate between those two kinds of sites.

► The acidity of about 2000 particulate matter samplers from aircraft and ground-based monitoring is analyzed.
► The ground-based samples were collected at about 50 urban or background sites in northern and southern China.
► The acidity increases and the acidic buffering capacity drops with the decreasing of the particle sizes.
► The acid precipitation has not been well controlled, and it even shows an increasing tendency in China lately.