Diurnal variation of number concentration and size distribution of ultrafine particles in the urban atmosphere of Beijing in winter.

Number concentration and distribution of airborne particles in the size range 5.6 to 560 nm diameter were measured in Beijing for a 15-d period in winter 2005. Daily average number concentrations of nucleation mode (5.6-20 nm), Aitken mode (20-100 nm), and accumulation mode (100-560 nm) particles, and total particles were 17500, 32000, 4000, and 53500 cm(-3), respectively. Average particle size distribution was monomodal with a mode diameter of about 40 nm at night and bimodal with mode diameters of about 10 and about 40 nm during the daytime. New particle formation events, which were connected to diurnal variation of nucleation mode particles, were observed in more than half of the observation days. The events often started around 10:00-11:00 Chinese Standard Time (CST) and ended up after 3-4 h. Concentrations of Aitken and accumulation mode particles increased from midnight and reached their maxima at about 10:00 CST, and then decreased and became the lowest in the afternoon. Analysis of diurnal cycles in traffic volume and meteorological parameters revealed that the accumulation of the particles in Aitken and accumulation modes in the morning was influenced by formation of an inversion and increase in vehicle emission, and dispersion of such particles in the afternoon was associated with more effective vertical mixing and higher wind speed.

[Regional PM pollution in Beijing and surrounding area during summertime].

The air quality in Beijing and surrounding area is influenced by local emission and regional transport. To study the characteristics of regional pollution, PM (particulate matter) samples were collected simultaneously at 4 sites including Tsinghua University (TH) and Miyun reservoir (MY) in Beijing, Renqiu (RQ, Hebei Province), and Shangdu (SD, Inner Mongolia) during August, 2007, and temporal/spatial distributions of PM2.5 mass concentrations along with 22 elements in TSP were characterized. PM2.5 mass concentrations were quite different at 4 sites, following the sequence as RQ > TH > MY > SD. The highest concentrations of pollution-derived elements S, Zn, Pb, Cu, As, Sb, Ni, Cd, In, Se were found in RQ, showing the most intensive anthropogenic influence around this region, and their lowest variation indicated that the pollution mostly came from local sources. Controlled by the meteorological factors, highest daily variations of these elements were found at SD with relative lower concentrations. The correlation coefficients of S, Pb, Cd, In, As, Zn concentrations between TH and MY were all higher than 0.70, which implies similar sources for these elements at the 2 sites in Beijing. At the beginning and the end of the Sawtooth pollution episode in Beijing, concentrations of most elements in Miyun were comparable with the lowest concentrations at Shangdu observed during the sampling period, which means Miyun could well represent the regional characteristics of clean air mass from the northwest. Uniform spatial distribution of high sulfate was found (about 10 microg/m3) at the peaks of Sawtooth episode, which implies the important contribution from secondary aerosol during the regional pollution. Variable sources of PM at each site and their regional influence were discussed based on the different characteristics of elemental enrichment factors.

[Characteristics of polycyclic aromatic hydrocarbons (PAHS) on airborne particulates in Beijing].

Total suspended particulates (TSP) samples were collected from Sep., 2003 to Jul., 2004 in Beijing, and 15 kinds of PAHs, ranging from 3 to 7 rings were analyzed. The maximum concentrations sigma PAHs and BaP were 705 ng/m3 and 52 ng/m3 respectively. Average sigma PAHs concentrations in four seasons were 46 ng/m3, 16 ng/m3, 52 ng/m3 and 268 ng/m3 respectively; and the average BaP concentrations in four seasons were 2.8 ng/m3, 0.23 ng/m3, 3.3 ng/m3, 16 ng/m3 respectively. Regarding to the meteorological parameters, precipitation distinctly lowered the concentration; in heating period, PAHs concentrations fall with the temperature goes up, but there is no obvious relation between concentration and temperature in non-heating period; the increase of wind speed level causes the decrease of PAH concentrations in the heating period, but relation between PAH concentrations and wind speed varied with aromatic rings of PAHs and levels of wind speed in the non-heating period.