Assessing the Marginal Impact of a Trip on Population Exposure to Air Pollution

Abstract

Purpose: There are different reasons to assume that not every vehicle kilometre yields the same environmental impact. For instance, some vehicle kilometres are driven at high speeds on highways, while others are driven at low speeds in urban environments. This will have an impact on the resulting exhaust missions. Furthermore, the timing of a trip determines its impact on the resulting concentration levels. Pollutants emitted during trips at night will have a larger impact on the ground-level concentrations than emissions exhausted during the day, due to the greater atmospheric stability. And, concerning the impact on exposure, emissions produced in cities will affect a larger number of people than emissions exhausted in sparsely populated areas. These aspects are examined in this paper using an integrated model chain involving an activity based traffc demand model (to assess people's travel behavior), an emission model (to convert the trips into emissions) and a pollutant concentration module(to stimulate detailed concentration maps and assess the impact of each trip on the resulting concentration level). By combining the model output with detailed population information, the marginal impact of a trip on the population exposure to NO2 was assessed. Results demonstrate that not every vehicle kilometre and not every trip motive yields the same impact on the population exposure.