The temporal variations of size–segregated PM, OC and EC in
the aerosols of Beijing from August 2009 to August 2011 are shown
in Figure 3. PM, OC, and EC experienced significant variations
during the two–year observation. The average concentration in fine
particles (PM2.1, 100.7±77.2 μg m–3) was comparable with that in
coarse particles (PM>2.1, 126.7±70.2 μg m–3) during the two years.
Considering the Chinese Grade–II standards of 35 μg m–3 (annual
average) for PM2.5 (Ministry of Environmental Protection of the
People's Republic of China, 2012), air pollution resulting from fine
particles was serious in Beijing. The average OC concentrations in
PM2.1 and PM>2.1 were 22.5±11.5 μg m–3 and 15.9±5.6 μg m–3
during the two years, respectively. The average EC concentrations
in PM2.1 and PM>2.1 were 2.7±1.5 μg m–3 and 1.1±0.7 μg m–3 during
the two years, respectively. The results indicated that carbonaceous
species enriched more in fine particles than in coarse
particles. The seasonal average concentrations of OC and EC
distributed in PM2.1 and PM>2.1 are illustrated in Figure 4. During
the two–year observation, OC concentrations in PM2.1 followed the
order of winter>autumn>summer>spring (P2.1 among four
seasons. The EC concentrations in both PM2.1 and PM>2.1 were
significantly (P