London, Aug 10 (IANS): Next time when you roll down car windows for some fresh air, think again. According to researchers, including one of Indian-origin, car users from the world's least affluent cities are exposed to at least 80 per cent more in-car air pollution because they rely heavily on opening their windows for ventilation.

For the study, published in the journal Science of The Total Environment, the research team investigated air pollution exposure levels for commuters in 10 different global cities across the world, including Chennai.

"To be blunt, we need as many cars as possible off the road, or more green vehicles to reduce air pollution exposure," said study researcher Prashant Kumar from the University of Surrey in the UK.

"Air-conditioned cars are unattainable for many poor and vulnerable commuters across the world, but our data is clear and coherent for all 10 participating cities," Kumar added.

According to the World Health Organisation (WHO), air pollution kills an estimated seven million people worldwide every year and nine out of 10 people breathe air with high levels of pollutants.

The research team investigated PM2.5 and PM10 exposure levels inside vehicles during peak hours in the morning and evening, as well as off-peak hours in the middle of the day.

The scientists measured how exposure levels changed when drivers used recirculation systems, fans and simply opened the windows.

The study discovered that drivers in some of the world's poorest cities experienced higher levels of in-car pollution.

Irrespective of the city and car model used, a windows-open setting showed the highest exposure, followed by fan-on and recirculation.

Pollution exposure for windows-open during off-peak hours was 91 per cent and 40 per cent less than morning and evening peak hours, respectively.

The study also found that the windows-open setting exposed car passengers to hotspots of air pollution for up to a third of the total travel length.

The findings also showed that commuters who turn on the recirculation are exposed to around 80 per cent less harmful particles than those who open their car windows.

Car cabin filters were more effective in removing pollution than fine particles, suggesting that if new cars had more efficient filters, it could reduce the overall exposure of car commuters.

"The study has drawn important conclusions that can help commuters make decisions in their day-to-day lives to protect their health," said study researcher Abdus Salam from the University of Dhaka in Bangladesh.

"Simple choices, like travelling during off-peak hours, can go a long way in reducing their exposure to air pollution," Salam said.