The study shows that the mass concentration of black carbon - carbon particles released by incomplete combustion of fuel - reduced from 15 micrograms per cubic metre on December 31 to 7.6 micrograms per cubic metre on January 5. The test was conducted at the monitoring station on the university campus in Manesar.

"Vehicles are a major source of black carbon after wood burning. Stranded vehicles, in particular, are responsible for emitting black carbon. We have noticed that due to reduction in traffic jams during the odd-even scheme, the level of unburnt carbon in the atmosphere has come down," said Dr P C S Devara, president of Indian Aerosol Science and Technology Association, who mentored the students during the study.

According to the United Nations Environment Programme, black carbon is a sooty substance, which is a solid component of fine particulate matter (PM2.5). It has severe health impacts, including cardiovascular and respiratory diseases, and also contributes to climate change. Vehicles are responsible for nearly 20% of black carbon emissions globally, and diesel vehicles, in particular, are a major contributor to emissions.

Talking about the mechanism used for the study, Munshi Pavel Alam, a student of BSc (Earth Sciences) said, "We used data from the air monitoring system installed on our campus in Manesar and data provided by SAFAR (System of Air Quality and Weather Forecasting And Research) of the ministry of earth sciences. The team comprising two mentors and three students used a Seven Beam Aethalometer (instrument to measure suspended particles) to measure the concentration of black carbon and an aerodynamic particle sizer to measure PM levels."

The study brought out the correlation between the drop in time required to cover a particular distance during the odd-even scheme and the reduction in the consumption of fuel, which reportedly led to the decline in the concentration of black carbon in the air.

"For instance, a distance of 70km, which was earlier covered in more than two hours, can now be covered in just over an hour. This directly relates to approximately 30% reduction in fuel consumption for the same distance travelled on odd-even days, which led to reduction in black carbon in the atmosphere," Alam said.

Doctors in the city said the drop in levels of black carbon is a good sign and have welcomed the news, saying that black carbon can be carcinogenic.

"Black carbon particle is one of the main components of PM 2.5. Reduction in their concentration is definitely a good sign. PM 2.5 are extremely small particles that go straight to the lungs and can cause severe respiratory diseases. Even if there is a decrease in only one component of particulate matter, it should be seen as an achievement. However, it is too early to say that there is reduction in the level of overall air pollution in the city," said Dr Himanshu Garg, another pulmonologist.