Abstract. The ozone weekend effect (OWE) was first investigated in the metropolitan area of Beijing-Tianjin-Hebei (BTH), China, using in situ measurements from the Atmospheric Environment Monitoring Network from July 2009 to August 2011. The results indicate that there is an obvious weekly periodical variation in the surface ozone concentration. There is a lower ozone concentration from Wednesday to Friday (weekday) and a higher concentration from Saturday to Monday (weekend) at all the locations of the study. NO x also displays a weekly cycle, with the maximum level occurring on weekdays and the minimum level on weekends, especially later on Sunday night and early Monday morning. This pattern may be responsible for the higher concentration of ozone on weekends. Additionally, the vertical variations in O 3 and NO x from the 8 m, 47 m, 120 m and 280 m observation platforms on the 325 m Beijing meteorological tower displayed obvious weekly cycles that corresponded to the surface results.A smaller decrease in volatile organic compounds (VOCs; using CO as a proxy) and much lower NO x concentrations on the weekend may lead to higher VOC / NO x ratio, which can enhance the ozone production efficiency in VOC-limited regime areas. Additionally, a clear weekly cycle in the fine aerosol concentration was observed, with maximum values occurring on weekdays and minimum values occurring on weekends. Higher concentrations of aerosol on weekdays can reduce the UV radiation flux by scattering or absorbing, which leads to a decrease in the ozone production efficiency. A significant weekly cycle in UV radiation, consistent with the aerosol concentration, was discovered at the Beijing meteorological tower site (BJT), validating the assumption. A comprehensive understanding of the ozone weekend effect in the BTH area can provide deep insights into controlling photochemical pollution.

Acknowledgment. This work was funded by the Office of Basic Energy Sciences of the Department of Energy.We wish to thank Prof. D. Dooley of Amherst College for the use of the 1000-W Xe lamp. active agents to the surface in domains with spectroscopic studies will make it possible to examine photochemistry in the two dimensions of the semiconductor surface and to make time-resolved studies of electron transfer along this plane. ReaistrvNo. Rhodamine 6G, 989-388: Rhodamine B. 81-88-9: (35) h f i n m d , P. A.; Camgrove, T. P.; Stmve, w. s. J . phys, Chem. Eosin-Y,We study the agglomerate morphology of a carbonaceous soot aerosol extracted from a premixed methaneloxygen flame during combustion by the use of real-time optical structure factor measurements and subsequent transmission electron microscope examination of the settled agglomerates. We find a fractal morphology is maintained during the agglomeration growth of the aerosol with a fractal dimension D = 1.62 f 0.06. The TEM analysis also shows this fractal morphology with D = 1.72 f 0.10. These values of D are on the low side of the range D = 1.7-1.9 expected from diffusion-limited cluster aggregation models.

ABSTRACT:The reactive compatibilization effect of a small molecule, bismaleimide (BMI), on poly(butylene terephthalate) (PBT)/low-density polyethylene (LDPE) and PBT/ethylene propylene diene (EPDM) rubber blends were investigated. All the blends were prepared by melt blending in the mixing chamber of a Haake Rheocord. The particle size of dispersed phase was reduced by Ͼten times by adding 1.2 wt % of BMI as observed with scanning electron microscopy. The torque-time curve recorded during mixing showed that the addition of BMI leads to a significant increase in the viscosity of PBT, LDPE, EPDM, and the blends. This indicates that a chemical reaction has taken place. It was confirmed that free radicals are involved in the reactions because the addition of a stabilizer to the blends has removed all the compatibilizing effect, and the torque-time curve does not show any increase in viscosity. A possible mechanism of compatibilization is proposed. The shear forces during melt mixing cause the rupture of chemical bond in the polymers, which form macroradicals of PBT, LDPE, or EPDM. These macroradicals react with BMI to form PBT-BMI-LDPE or PBT-BMI-EPDM copolymers. These in situ-formed copolymers act as compatibilizers to give a significant refinement of the blend morphology.

The performance of acrylonitrile-butadienestyrene (ABS) core-shell modifier with different grafting degree, acrylonitrile (AN) content, and core-shell ratio in toughening of poly(butylene terephthalate) (PBT) matrix was investigated. Results show PBT/ABS blends fracture in ductile mode when the grafting degree is high, and with the decrease of grafting degree PBT/ABS blends fracture in a brittle way. The surface of rubber particles cannot be covered perfectly for ABS with low grafting degree and agglomeration will take place; on the other hand, the entanglement density between SAN and PBT matrix decreases because of the low grafting degree, inducing poor interfacial adhesion. The compatibility between PBT and ABS results from the strong interaction between PBT and SAN copolymer and the interaction is influenced by AN content. Results show ABS cannot disperse in PBT matrix uniformly when AN content is zero and PBT/ABS fractures in a brittle way. With the addition of AN in ABS, PBT/ABS blends fracture in ductile mode. The coreshell ratio of ABS copolymers has important effect on PBT/ ABS blends. When the core-shell ratio is higher than 60/40 or lower than 50/50, agglomeration or cocontinuous structure occurs and PBT/ABS blends display lower impact strength.