Evaluating near highway air pollutant levels and estimating emission factors: Case study of Tehran, Iran

- Size segregated PM and CO were measured on a highway roadside and in a tunnel.
- Sharp increase of pollutant levels found in 100-150 m downwind of highway shoulder
- The EFs for CO and PM10 were estimated to be ~ 4-12 and 0.1-0.2 g/km, respectively.
- Variation of EFs under real working condition with speeds was determined.
- Particle aging and size change by distancing downwind of highway were evaluated.

A field sampling campaign was implemented to evaluate the variation in air pollutants levels near a highway in Tehran, Iran (Hemmat highway). The field measurements were used to estimate road link-based emission factors for average vehicle fleet. These factors were compared with results of an in tunnel measurement campaign (in Resalat tunnel). Roadside and in-tunnel measurements of carbon monoxide (CO) and size-fractionated particulate matter (PM) were conducted during the field campaign. The concentration gradient diagrams showed exponential decay, which represented a substantial decay, more than 50-80%, in air pollutants level in a distance between 100 and 150 meters (m) of the highway. The changes in particle size distribution by distancing from highway were also captured and evaluated. The results showed particle size distribution shifted to larger size particles by distancing from highway. The empirical emission factors were obtained by using the roadside and in tunnel measurements with a hypothetical box model, floating machine model, CALINE4, CT-EMFAC or COPERT. Average CO emission factors were estimated to be in a range of 4 to 12 g/km, and those of PM10 were 0.1 to 0.2 g/km, depending on traffic conditions. Variations of these emission factors under real working condition with speeds were determined.

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