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RISS 인기검색어
- 검색키워드
- 저자 : DeShazo, J.R. (검색결과 3 건)
- 무료
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Choi, Wonsik,Ranasinghe, Dilhara,DeShazo, J.R.,Kim, Jae-Jin,Paulson, Suzanne E. Elsevier 2018 Environmental pollution Vol.233 No.-
<P><B>Abstract</B></P> <P>Epidemiological studies have shown that exposure to traffic-related pollutants increases incidence of adverse health outcomes. Transit users in cities across the globe commonly spend 15–45 min or more waiting at transit stops each day, often at locations with high levels of pollution from traffic. Here, we investigate the characteristics of concentration profiles of ultrafine particles (UFP) with 5 m spatial resolution across intersections, to determine the best place to site transit stops to minimize exposures. Cross-intersection UFP profiles were derived from 1744 profiles covering 90 m before and after each intersection center with a mobile monitoring platform. Measurements were made at 10 signalized intersections located at six urban sites, each with a distinct built environment, during both mornings and afternoons. Measurements were made within 1.5 m of the sidewalk and approximately at breathing height (1.5 m above ground level) to approximate sidewalk exposures. UFP profiles were strongly influenced by high emissions from vehicle stops and accelerations, and peaked within 30 m of intersection centers; from there concentrations decreased sharply with distance. Peak concentrations averaged about 90% higher than the minima along the block. They were accompanied by more frequent and larger transient concentration spikes, increasing the chance of people near the intersection being exposed to both short-term extremely high concentration spikes and higher average concentrations. The decays are somewhat larger before the intersection than after the intersection, however as siting transit stops after intersections is preferred for smooth traffic flow, we focus on after the intersection. Simple time-duration exposure calculations combined with breathing rates suggest moving a bus stop from 20 to 40–50 m after the intersection can reduce transit-users' exposure levels to total UFP substantially, in proportion to the reciprocal of the magnitude of elevation at the intersection.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Roadway pollutant concentrations generally peak within ±30 m from the intersection. </LI> <LI> Pollutant concentrations decrease sharply with distance to local minima at ∼45 m. </LI> <LI> Placing bus stops 40–50 m from intersections significantly reduces UFP Exposure. </LI> <LI> UFP enhancement is correlated queue lengths in the intersections. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Choi, W.,Ranasinghe, D.,Bunavage, K.,DeShazo, J.R.,Wu, L.,Seguel, R.,Winer, A.M.,Paulson, S.E. Elsevier Pub.Co 2016 The Science of the total environment Vol.553 No.-
This study attempts to explain explicitly the direct and quantitative effects of complicated urban built-environment on near-road dispersion and levels of vehicular emissions at the scale of several city blocks, based on ultrafine particle concentrations ([UFP]). On short timescales, ultrafine particles are an excellent proxy for other roadway emissions. Five measurement sites in the greater Los Angeles with different built environments but similar mesoscale meteorology were explored. After controlling for traffic, for most sampling days and sites, morning [UFP] were higher than those in the afternoon due to limited dispersion capacity combined with a relatively stable surface layer. [UFP] at the intersection corners were also higher than those over the sampling sites, implying that accelerating vehicles around the intersections contributed to [UFP] elevation. In the calm morning, the areal aspect ratio (Ar<SUB>area</SUB>), developed in this study for real urban configurations, showed a strong relationship with block-scale [UFP]. Ar<SUB>area</SUB> includes the building area-weighted building height, the amount of open space, and the building footprint. In the afternoon, however, when wind speeds were generally higher and turbulence was stronger, vertical turbulence intensity σ<SUB>w</SUB> was the most effective factor controlling [UFP]. The surrounding built environment appears to play an indirect role in observed [UFP], by affecting surface level micrometeorology. The effects are substantial; controlling for traffic, differences in Ar<SUB>area</SUB> and building heterogeneity were related to differences in [UFP] of factors of two to three among our five study sites. These results have significant implications for pedestrian exposure as well as transit-oriented urban planning.
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