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.

[Exhaust Emission Characteristics of Typical Alkanes from Heavy-Duty Diesel Vehicles Based on a Portable Emission Measurement System].

The on-road emissions of typical alkanes from 11 heavy-duty diesel vehicles with different emission standards (from China Ⅰ to China Ⅳ) were tested using a portable emission measurement system(PEMS) and quantified by gas chromatography-mass spectrometry (GC-MS). Our aim was to analyze the emission characteristics of typical alkanes in heavy-duty diesel vehicle exhaust. The results show that the emission standard significantly affected the emission factors (EFs) of n-alkanes and hopanes. Vehicles with higher emission standards had lower EFs. Compared with China Ⅰ vehicles, the total EFs of n-alkanes, 17α(H),21ß(H)-C30 hopane (C30-hopane), and 22S- and 22R-17α(H),21ß(H)-homohopane (22S-C31 and 22R-C31 homohopane) from China Ⅳ vehicles were significantly reduced by 72.23%, 64.95%, 70.78%, and 74.68%, respectively. The peak carbon numbers of gaseous n-alkanes were 17 to 18, while they were 18 to 21 in particulate n-alkanes. The 22S-C31 homohopane/(22S-C31 homohopane + 22R-C31 homohopane) ratios ranged from 0.46 to 0.56, with an average of 0.50, which conform to the characteristics of hopanes in petroleum. The total EFs of n-alkanes had a good linear relationship with the total EFs of C30-hopane, and the R2 was 0.9268. Furthermore, the driving conditions had a great influence on the emissions of n-alkanes and hopanes. Specifically, the EFs of n-alkanes and hopanes on non-highway roads were 1.69 to 2.42 times greater than those on highways.

[Development of the driving cycle-based mobile emission model (DCMEM)].

Vehicle specific power (VSP) and engine stress (ES) were introduced to reflect the driving characteristics of vehicles in China. Emission rates of 60 BIN based on VSP and ES for light-duty vehicles were calculated on the basis of the on-board emission test data in 5 cities of China. The driving cycle-based mobile emission model (DCMEM) was developed to simulate CO, NOx and HC emission factors of light-duty vehicles for different cities or driving cycles. The differences in CO and NOx emission factors between the DCMEM simulation results and the emissions testing results were less than 10%, and less than 18% for HC.

[Application study of IVE vehicle emission model].

This paper introduced IVE model and presented the method to quantify the main parameters by taking Beijing city as a case. Emissions from different vehicle fleets of Beijing were calculated using IVE model. The results show that emissions factors of buses and trucks were much higher, especially for PM, which were 14 and 44 times those of passenger cars. The daily CO, VOC, NO, and PM emissions of vehicles in Beijing city were 2767.4, 182.5, 353.8 and 7.1 t respectively. Common light duty vehicles were the main emission source of CO and VOC, with the contribution of 42.0% and 34.7% respectively, Trucks were the largest contributor of NO, and PM emissions, with the contribution of 66.3% and 83.0% respectively. The methodology and calculating results of MOBILE6 and IVE model were compared, and advantages of IVE model's application in China were discussed.