Journal of Civil and Environmental Engineering

Determination of Safe Roadway Buffer Width to Protect Human Health from NO₂ Exposure: A Case Study for Grand Prairie, TX

Abstract

Hetal Bhatt ,Melanie L. Sattler *,Stephen P. Mattingly

According to the U.S. Environmental Protection Agency (EPA), in 2010 mobile sources in the U.S. contributed
58% of carbon monoxide (CO), 56% of nitrogen oxide (NOx), and 33% of Volatile Organic Compounds (VOCs). Onroad
sources also emit a variety of air toxics, including benzene, toluene, and xylenes. The case study presented here
determines a safe roadway buffer width to protect human health from nitrogen dioxide (NO2) exposure along an arterial
in Grand Prairie, Texas. NO2 health effects include eye, nose, throat, and lung irritation; cough; shortness of breath;
tiredness and nausea. In the Dallas Fort Worth region, where Grand Prairie is located, on-road vehicles contribute
about half of NOx emissions.
Vehicle NOx emission rates along Great Southwest Parkway were measured using a Horiba 1300 OBS onboard
emission measurement system, to determine a maximum g/mile emission factor for the corridor. Hourly DFW
meteorological data for a 5-year period was processed using CAL3QHCR to determine the 10 worst-case hourly
meteorological combinations. The maximum emission factor and worst-case meteorological conditions were input into
the line source dispersion model CALRoads View to determine worst-case NO2 concentrations at 5- m intervals away
from the roadway. CALRoads View output was post-processed in Arc View GIS to plot concentrations at receptor
locations.
Worst-case concentrations were compared to the 1-hour NO2 National Ambient Air Quality Standard (100 ppb). For
the current Great Southwest traffic volume, it was found that the standard would not be exceeded. Additional CALRoads
View runs were conducted to determine how much the traffic volume could increase, and still avoid exceedances
outside a 20-foot buffer width, which is a common setback distance in residential areas. It was determined that the
traffic volume could increase by a factor of 10 and still protect human health from NO2 impacts, using a 20-foot buffer.