Why You Could Suffer From More Pollution While Driving A Car Than Riding A Bus On Highways? IIT Kharagpur Researchers Find out

New Delhi: Congestion and hazardous vehicular air pollution, which puts our health at risk, in city roads are a well-known fact. Studies done by Central Pollution Control Board in six Indian cities (Bangalore, Chennai, Delhi, Kanpur, Mumbai, and Pune) revealed that 30-50 percent of the ambient particulate matter originates from the vehicular exhaust and re-suspended road dust. To escape from the city’s congestion and pollution, we often head towards our national highways. But, how much of hazardous pollutants are you exposed to when you are travelling a long distance in your car on highways for leisure trips or for professional activities? A recent study done by researchers from Indian Institute of Technology (IIT) – Kharagpur got an answer. The study examined the contribution of different travel modes to passengers’ pollutant exposure for a long distance travel on a national highway in India, and revealed that the selection of a travel mode for long distance journey on a highway can significantly influence the passenger exposure level to the pollutants. The study also observed that the vehicle exhaust and road dust resuspension for PM2.5, and self-pollution of the car for carbon monoxide (CO) are the major polluting sources on national highway.

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The study titled ‘A comparison of personal exposure to air pollutants in different travel modes on national highways in India’ was carried out on a busy national highway of the length of 200 km, connecting Bhadrachalam in Telangana State with Vijayawada in Andhra Pradesh. The researchers gathered data by traveling this stretch for almost two months. In-vehicle concentrations were measured in the bus and the car (both diesel-powered), two most used travel modes on the study route.  They carried instruments such as the EVM-7 and the EPAM-5000 (Environment Particulate Air Monitor) to measure particulate matter and carbon monoxide concentration in the air.

The researchers found that the exposure to PM2.5 concentration was lowest in car if air-conditioning is turned on, but at the same time CO exposure was highest in the same case. In contrast, it was observed that although PM2.5 exposure was found to be higher in bus than car with its AC turned on, it was lower than the exposure in car without AC. Importantly; it was also found that CO exposure was lowest in bus when compared to car, with and without AC turned on. PM2.5 exposure levels in the car (without AC) were found to be 1.7 times the exposures in the car (with AC) and 1.4 times in bus.

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But why are the cars not a good mode to travel, rather bus is? The researchers in their study mentioned the possible reasons for higher PM 2.5 concentrations inside car with windows rolled down than the bus – car’s small size, the short distance between the car and road in comparison to bus whose larger size restricts the exhaust to get inside, and the speed at which a car travels, resulting in higher inflow of pollutants inside the car. Furthermore, the reason behind CO being recorded higher in car than bus, is the emissions leakage from car’s exhaust into the car-cabin – commonly referred as self-pollution.

Also, study noted that the mass exposure to pollutants for passengers in the car was highest, despite car taking less time than bus to travel same distance. In addition, the study indicated that for all travel modes, mass exposures in cities were higher when compared to open highway.

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