Meteorological Condition Analysis of a Typical Fine Particle Pollution Event in the Piedmont Region of Beijing

Inhalable particulate matter(PM_(10)) is the primary pollutant in Beijing during winter over the past few years.Fine particles(PM_(2.5)),one of the components of PM_(10),has the typical character of regional pollution which results from the specific terrain and meteorological conditions in the northern parts of Beijing.Four typical fine particle pollution events appeared in Beijing during December 2007,and related meteorological conditions have been analyzed in this paper.The results show that there is direct correlation between the period of accumulating/removal of fine particles and the maximum mass concentration of PM_(2.5) as well as the meteorological conditions.The daily average mass concentration of PM_(2.5) on December 26 during the accumulating process from 23 to 26 reached 313.4 μg/m~3,more than two times the PM_(10) national standard value(150 μg/m~3,according to the ambient air quality standard,GB3095-1996) and more than 11 times the PM_(2.5) guidance value(25 μg/m~3) of the World Health Organization.According to observation data and simulation results for these events,it was found that the weather conditions,such as persistent south winds and specific local circulation at the bottom boundary layer,were the main reasons for the serious fine particles pollution.The weather caused fine particles emitted in the south area of Heber to accumulate continuously in Beijing with an accumulation rate of 96.7(μg/m~3) per day.