New Delhi, June 29 -- Heavy-duty trucks and buses comprise just 2.5-3% of vehicles on India's roads but account for about 35-36% of transport-related fine particulate matter (PM2.5) emissions, according to a study by the ministry of road transport and highways (MoRTH). The findings strengthen the case for tighter emission standards and faster fleet modernization, both being key to the government's proposed BS VII framework.

Transport emissions include pollutants such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter. But experts say it is fine particulate matter (PM2.5) that poses the greatest public health risk as it can penetrate deep into the lungs and bloodstream.

"According to our study, heavy...