Characterizing spatial variability of air pollution from vehicle traffic around the Houston Ship Channel area

- Heavy-duty vehicles were the largest contributor of traffic-related PM2.5 concentrations in the Houston Ship Channel area.
- Highest concentrations of traffic-related PM2.5 and NOx occurred in winter.
- Concentrations of traffic-related PM2.5 and NOx decreased by nearly 40% within 500 meters of major roads.

Mobile emissions are a major source of urban air pollution and have been associated with a variety of adverse health outcomes. The Houston Ship Channel area is the home of a large number of diesel-powered vehicles emitting fine particulate matter (PM2.5; ≤2.5 μm in aerodynamic diameter) and nitrogen oxides (NOx). However, the spatial variability of traffic-related air pollutants in the Houston Ship Channel area has rarely been investigated. The objective of this study is to characterize spatial variability of PM2.5 and NOx concentrations attributable to on-road traffic in the Houston Ship Channel area in the year of 2011. We extracted the road network from the Texas Department of Transportation Road Inventory, and calculated emission rates using the Motor Vehicle Emission Simulator version 2014a (MOVES2014a). These parameters and preprocessed meteorological parameters were entered into a Research LINE-source Dispersion Model (RLINE) to conduct a simulation. Receptors were placed at 50 m resolution within 300 m to major roads and at 150 m resolution in the rest of the area. Our findings include that traffic-related PM2.5 were mainly emitted from trucks, while traffic-related NOx were emitted from both trucks and cars. The traffic contributed 0.90 μg/m3 PM2.5 and 29.23 μg/m3 NOx to the annual average mass concentrations of on-road air pollution, and the concentrations of the two pollutants decreased by nearly 40% within 500 m distance to major roads. The pollution level of traffic-related PM2.5 and NOx was higher in winter than those in the other three seasons. The Houston Ship Channel has earlier morning peak hours and relative late afternoon hours, which indicates the influence of goods movement from port activity. The varied near-road gradients illustrate that proximities to major roads are not an accurate surrogate of traffic-related air pollution.

Annual average of predicted PM2.5 concentrations (μg/m3) and NOx concentrations (μg/m3) attributed to the running exhausts of motor vehicles and diesel trucks, respectively. The black arrows show the locations of two “hotspots”. A) PM2.5 from all vehicles; B) PM2.5 from diesel-powered heavy duty trucks; C) NOx from all vehicles; and D) NOx from diesel-powered heavy duty trucks.437