Estimation of real-world traffic emissions for CO, SO, and NO through measurements in urban tunnels in Tehran, Iran.

Mobile sources are considered to be one of the most important sources of air pollution among which are motor vehicles, recognized as the major contributor of air pollutants in urban areas. To determine the emissions for CO, SO, and NO from motor vehicles as part of the attempt to realize the extent of traffic air pollution, measurements were carried out in two heavily traversed traffic tunnels in Tehran metropolitan area. The concentrations of pollutants and metrological and traffic data were collected through intensive measurements from September 27 to October 17, 2016. Resalat Tunnel fleet was composed of about 10% diesel-fueled vehicles and 90% non-diesel-fueled vehicles while throughout the entire duration of our campaign, only non-diesel-fueled vehicles traversed Niayesh Tunnel. Under an average traffic speed of 43 km h, emission factors from Resalat Tunnel campaign were measured to be (6.59 ± 2.69)E+3, (1.42 ± 0.84)E+2, and 6.80 ± 4.99 mg km for CO, SO, and NO, respectively. These values were respectively 11% higher, 22% lower, and 40% higher than those from Niayesh Tunnel measurements which were recorded at a traffic speed of 30 km h. Current results indicate that the vehicular emissions in certain countries, especially the developing ones and in this case, Iran, are quite different from those measured in developed countries and that the high emission levels of SO in Iran are associated with the high sulfur content of the gasoline.