Time-series analysis to study the impact of an intersection on dispersion along a street canyon

Abstract

This paper presents data analysis from the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study to assess the transport of ultrafine particulate matter (PM) across urban intersections. Experiments were performed in a street canyon perpendicular to a highway in Brooklyn, NY, USA. Real-time ultrafine PM samplers were positioned on either side of an intersection at multiple locations along a street to collect time-series number concentration data. Meteorology equipment was positioned within the street canyon and at an upstream background site to measure wind speed and direction. Time-series analysis was performed on the PM data to compute a transport velocity along the direction of the street for the cases where background winds were parallel and perpendicular to the street. The data were analyzed for sampler pairs located (1) on opposite sides of the intersection and (2) on the same block. The time-series analysis demonstrated along-street transport, including across the intersection when background winds were parallel to the street canyon and there was minimal transport and no communication across the intersection when background winds were perpendicular to the street canyon. Low but significant values of the cross-correlation function (CCF) underscore the turbulent nature of plume transport along the street canyon. The low correlations suggest that flow switching around corners or traffic-induced turbulence at the intersection may have aided dilution of the PM plume from the highway. This observation supports similar findings in the literature. Furthermore, the time-series analysis methodology applied in this study is introduced as a technique for studying spatiotemporal variation in the urban microscale environment.

The effect of a tall tower on flow and dispersion through a model urban neighborhood : Part 2. Pollutant dispersion

“…This article is part of a larger series of papers related to the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study field work. [7][8][9][10][11][12] These papers present the results of an intensive study that comprises field measurements, physical modeling, and computer simulations of the airflow and pollutant dispersion patterns within an urban neighborhood in Brooklyn, NY, USA, composed of three-story attached row houses, one 12-story building, and a major expressway.…”

The Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) field study methodology

“…One-second timeresolved data were used in other papers where forecasting tools were employed to examine temporal and spatial correlations. [26][27][28]…”

“…These are explored in complementary papers. [26][27][28] Similar to the DAPPLE study, 16 significant effort was expended during the B-TRAPPED study on wind tunnel and computational fluid dynamics modeling to explore transport phenomena in a generic representation of the Sunset Park neighborhood. These efforts were not discussed in this paper because they were beyond the scope of the field work.…”

NOx and CO Fluctuations in a Busy Street Canyon

“…Cross-correlation analysis has proved to be of value in understanding how airflow may vary between an enclosed portion of a canyon and intersections [25]. Here, we used cross-correlation to explore the lags between the appearance of pollutants at various locations, with node R1 taken as the reference (Figure 5a).…”