Air & Waste Management Association (A&WMA)

A quantitative approach to the traffic air quality problem: the traffic air quality index

The Traffic Air Quality (TAQ) model is a simple tool to estimate traffic fine particulate emissions on roadways (g/km) and can be used for both real-time analysis and for localized conformity analysis (“hot-spot” analysis for nonattainment areas) as defined by 40 CFR 93.123. This paper is a follow-up to a study published earlier regarding the development of the TAQ model. This paper shows how local air quality levels can be a factor in traffic management in nonattainment areas. Similar to the industrial source quotas measured in tons per year, it is proposed that road segments are to be assigned emission quotas (or TAQ indices) measured in pollutant mass emitted per road length (g/km) above which traffic-measures have to be taken to reduce the fine-particulates emissions on such road links. The TAQ model as well as traffic-rerouting measures along with the Intelligent Transportation System (ITS) protocols can be used to have a real-time control of the traffic conditions along expressways to maintain the fine-particulates emissions below the quota assigned per road link and consequently improving the over all local air quality in nonattainment areas.

Fine particulates, that is, those less than 2.5m in diameter (PM2.5) have been identified by the U.S. Environmental Protection Agency (EPA) to be one of the most dangerous of the pollutants known to adversely affect humans.1,2 They penetrate deep into the human lung and because of their relatively large surface area-to-volume ratio, adsorb and absorb other toxic pollutants in the air, thus delivering an enriched concentration of these toxic substances ultimately into the blood stream. Mobile sources are major contributors to air pollution in urban areas, hence, it is important to characterize and quantify the impact of traffic on air quality. Pollutants from transportation sources such as diesel and gasoline engines, brake dust, and tire/road dust are exacerbated during unstable conditions on expressways because of acceleration, deceleration, braking, and lane changing.

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