Wednesday, July 06, 2011

Estimating Road Dust Resuspension for Air Pollution Modeling

In the developing country cities, the vehicular exhaust emissions are increasing and is a nuisance with every day highs in the air pollution (especially particulates); more than the national and international standards. Among the vehicle types, passenger cars and motorcycles take the largest market share and are experiencing the highest growth rate in the recent years. In the big cities, transport sector tends to be the largest contributor to the growing air pollution problems and increasing health exposure problems.

See a video of the pollution exposure on the roads of Delhi, India. In a recent pole, looking at the published information on air quality monitoring from cities across the world, the city of Delhi was declared the most polluted city in the world (tied with Beijing, China) and also the "Asthma Capital" of India.

Also see "Who's more toxic - China and India?".

Also see "Rising Urban Challenges in India"

Besides the direct exhaust emissions, a major source of PM is the fugitive dust due to vehicular activity on the road. This resuspended dust includes (a) wind blown dust which settles on the road (b) wear and tear of tires and (c) dry deposits of other pollutants. For the emissions associated with the vehicular movement, this is the source of the most importance. Estimating the road dust emissions is not an easy process. As part of the SIM-air family of tools at UrbanEmissions.Info, here is a tool to estimate resuspended road dust emissions in a city.

(Also see Dust Busters on CAI-Asia network)

Assuming that the car weighs an average 2 tons and an average slit loading of 100 grams per square meter on the paved roads, following the empirical methodology presented in USEPA’s AP-42, I estimated an average of 30 gm/km of resuspended PM10 emissions.

This implies, every new car on road for 30 km a day, 6 days a week will resuspend 0.28 tons of PM10 annually.

When compared to an emission rate of 0.05 gm/km of PM (for a petrol based car with less than 1000 cc engine) is ~600 times more (=30/0.05). So, adding a car on the road is not the problem for air pollution, but the possible dust emissions due to an extra car on the road is.

See the list of databases for average emission factors.

Please note that the example calculations is based on the assumption that the average silt loading is 100 gm/m2, which could be lower if the city is administering wet sweeping or if the roads are generally wetter, often due to rains.

Download the v-dust, vehicular fugitive dust calculator, to better understand the parameters involved in these calculations.

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