Ultrafine particle (UFP) number and size distributions were simultaneously measured at five urban and rural sites during the summer of 2007 in Ontario, Canada as part of the Border Air Quality and Meteorology Study (BAQS-Met 2007). Particle formation and growth events at these five sites were classified based on their strength and persistence as well as the variation in geometric mean diameter. Regional nucleation and growth events and local short-lived strong nucleation events were frequently observed at the near-border rural sites, upwind of industrial sources. Surprisingly, the particle number concentrations at one of these sites were higher than the concentrations at a downtown site in a major city, despite its high traffic density. Regional nucleation and growth events were favored during intense solar irradiance and in less polluted cooler drier air. The most distinctive regional particle nucleation and growth event during the campaign was observed simultaneously at all five sites, which were up to 350 km apart. Although the ultrafine particle concentrations and size distributions generally were spatially heterogeneous across the region, a more uniform spatial distribution of UFP across the five areas was observed during this regional nucleation event. Thus, nucleation events can cover large regions, contributing to the burden of UFP in cities and potentially to the associated health impacts on urban populations. Local short-lived nucleation events at the three near-border sites during this summer three-week campaign were associated with high SO2, which likely originated from US and Canadian industrial sources. Hence, particle formation in southwestern Ontario appears to often be related to anthropogenic gaseous emissions but biogenic emissions at times also contribute. Longer-term studies are needed to help resolve the relative contributions of anthropogenic and biogenic emissions to nucleation and growth in this region.
Crystalline microwires of a phenyleneethynylene (PE) macrocycle self-assembled from solution exhibited superior photoconductive properties. Photoswitches fabricated with single wires afforded nA-scale photocurrents with on/off ratios of ca. 10(3). At a bias of 30 volts highest gain value achieved was up to 4.5. The stable and rapid responses to light qualify these microwire-based devices for excellent photoswitches or photodetectors.
Air and water samples were collected from Taihu Lake, East China through 2004 and analyzed for 33 congeners of polybrominated diphenyl ether (PBDE) and other seven brominated and chlorinated flame retardants. The annual concentration of total atmospheric PBDEs was 220 pg m(-3); BDE-209 was most abundant (average 41% of total PBDEs), followed by BDE-47 (17%) and BDE-28 (15%). The relative abundance of tetra- and tri-BDE congeners (including BDE-47, -28, -49, -66, and -17) instead of BDE-99 indicated that a specific penta-BDE formulation might be produced and/or consumed in this region. The source was confirmed by the analysis of air-water gas exchange, which was nearly at equilibrium in spring and summer but displayed strong volatilization flux in autumn and winter, especially for BDE-28, indicating the potential wastewater discharge of PBDEs into the lake. In addition to PBDEs, hexabromobenzene, 1,2-bis(2,4,6-tribromophenoxy)ethane, decabromodiphenylethane, and Dechlorane Plus were detected in air samples, with an annual mean concentration of 23 pg m-3 for decabromodiphenylethane, and <4 pg m(-3) for the others. (C) 2010 Elsevier Ltd. All rights reserved.