It may be recognized that identification and quantification of fugitive emissions are tedious and challenging task as these sources are irregular and often neglected. It is noteworthy that the fugitive emissions or non-point sources are not well defined and there can be no unique emission factor or method to estimate this component of the emissions. Among such fugitive sources, road dust non-exhaust emissions could be a significant emission source in urban areas. It has been reported by the emission inventory group of California State that road dust emissions were found to contribute about 15 % of the total dust emissions in urban areas. The particulate on the road may be an agglomerate of fine dust from the neighboring soils due to wind erosion, settlement of dust from tail pipe emissions or erosion of tires. Road dust (RD) emissions are resuspended particulate matter entrained in the urban street canopies due to wind erosion and movement of vehicles on the roads. RD emission is enriched with higher concentrations of toxic metals and organic compounds. Major elements reported both in the tail pipe particulate matter emissions and also in the road dust are Pb, Zn, Cd, Cu and Ba. Hence there is a need to quantify and characterize non-exhaust RD emissions. The current emission inventory data of urban cities in India do not include the road dust emissions.

In view of the importance of the non-exhaust road emissions, a study was undertaken to examine if RD emission in the city of Kanpur was a significant source of air pollution. For this purpose, extensive field sampling, laboratory analysis and computational exercises were undertaken.

Specifically, four sampling locations were identified on GT road (National Highway 91) representing variable traffic density. These locations on GT Road included: IIT Kanpur, Kalyanpur, Rawatpur and Tatmill. The RD samples were collected using a vacuum cleaner at all the study locations in three different seasons

- summer,
- post monsoon and
- winter.

The collected samples were analyzed for

(i) silt load on the road
(ii) particle size distribution and
(iii) chemical analysis - heavy metals, Total Carbon (TC) and Benzene Soluble Organic Fraction (BSOF).

The study concluded that RD emissions are significant source of air pollution in the city of Kanpur, which amounts to 25-50% of the tailpipe
emissions on GT road. The estimated RD emissions (gm/vehicle kilometer travel) in Kanpur were found to be about 300 times more than that of the values reported on roads in developed countries.

The chemical analysis of RD samples revealed that Zn and Pb were found to be 5-15 times higher than that of the background soil concentrations (of Kanpur). It was found that the relative concentration of Zn and Pb in RD matches with heavy metal emissions from vehicles, suggesting contributions from vehicle tailpipe particulate emissions to road dust. BSOF in dust samples was taken as an indicator of presence of toxic organic compound. BSOF in RD varied from 0.3-1.8%. This suggests that RD emissions are major sources of air pollution in cities like Kanpur and including heavy metals and organic compounds. Therefore, RD emissions should be considered in the overall emission inventory and measures shall be taken to control RD emissions.

Contact:

Mukesh Sharma
Prof., CE
IIT Kanpur, India.
Email: mukesh@iitk.ac.in