Wind Tunnel Testing of Vehicle Exhaust Dispersion at a Border Station

Land border checkpoints are high traffic areas with the potential to negatively affect local air quality. A wind tunnel study was conducted, for a planned border crossing upgrade in California, to assess indoor and outdoor air quality due to emissions from vehicular exhaust. The wind tunnel is the optimal tool to assess pollutant dispersion in highly complex building configurations, because accurate numerical simulations of dispersion for multiple wind directions and wind speeds are prohibitively expensive.

Vehicle exhaust has the potential to adversely impact air quality within the border station buildings, at the inspection booths, and at pedestrian areas around the site. Emissions from queues of idling vehicles upstream of inspection booths were evaluated in this study. This paper describes the wind tunnel testing methodology and data analysis. A scale model of the border station was installed in a boundary layer wind tunnel. Tracer gas concentrations due to vehicle sources were measured at points of interest for multiple wind directions and wind speeds. A fit function to the measured concentration data was then developed to allow for prediction of hourly and time-averaged NO2, PM2.5 and CO concentrations at air intakes, inspection booths and pedestrian areas, using hourly meteorological data from a nearby airport. Results were compared to Short Term Exposure Limits (STELs) and Time Weighted Average (TWA) exposure limits. Recommendations were provided for air intake placement, special HVAC features and procedures for inspection officers.