Black carbon consists of pure carbon in several linked forms. It is formed through incomplete combustion of fossil fuels, bio-fuel, and biomass, and is emitted in both anthropogenic and naturally occurring soot. Black carbon is notorious for causing human morbidity and premature mortality.

According to IIT-Guwahati’s findings, diesel-driven vehicles are the main causes of adding diesel carbon level in the traffic fleet nearby Lachit Nagar in Guwahati along Guwahati-Shillong Road. “Of them autorickshaws, which are mostly diesel driven, occupy a larger share. Apart from that, other heavy and light diesel-driven vehicles also contribute to black carbon and to the overall PM2.5 levels significantly,” IIT Guwahati said in its findings, adding that black carbon constituted 30-40 per cent share in the daily average PM2.5 levels. Black carbon concentrations, according to the findings, change with seasons drastically. “In monsoon it has decreased by about 47 per cent as compared to values observed in the winter season, considered to be the worst season for air pollution in the city,” IIT-Guwahati findings said.