In the study, “Evolution of size and composition of fine particulate matter in the Delhi megacity during late winter”, carried out by IIT-Kanpur, winter air pollution data was analysed at IIT-Delhi and Manav Rachna University in Faridabad. The influence of vehicular density was found to be a key feature in the formation of primary and secondary aerosols.
The researchers assessed the aerosol size and change in composition of particles during late winter, analysing data at both sites from February to March 2018. It found Delhi’s aerosols to be more “acidic” compared with those at Manav Rachna University.
Such high acidic conditions were responsible for promoting acid-catalysed secondary organic aerosols in the air, which had the potential to cause more damage to human health compared with primary aerosols, said experts.
“Further, organic aerosol families (amines and hydrocarbons) and inorganics, such as chloride and nitrates, also showed distinct concurrent diurnal growth patterns at IIT-Delhi,” the report stated. The researchers included those from Laboratory of Atmospheric Chemistry, Switzerland, Geosciences Division of Physical Research Laboratory at Ahmedabad and Department of Civil and Infrastructure Engineering at IIT-Jodhpur.
“Our study indicates that prevailing local conditions of high vehicular density and heterogeneity and the presence of growth-promoting factors, such as acidity and relative humidity conditions, significantly affect the growth of fine particulate matter,” the study added.
Sachchida N Tripathi, one of the researchers, said the two sites acted as a good representation of Delhi and NCR as a whole. Delhi was characterised largely by vehicular density, along with impact from power plants in the vicinity as well as waste burning.
“Delhi’s air was more acidic as it had more sulphur content compared with nitrates or ammonium levels. More sulphate in the air is generally from vehicles or power plants, with vehicles likely to be the lead cause in this case. This highly acidic air is playing a great role in fine aerosol particles in Delhi compared with Faridabad,” added Tripathi.
Aerosols are either emitted directly in the atmosphere in the form of primary aerosols, or can be produced in the atmosphere after a combination of gases and particles. Describing these aerosols to be close to PM1, Tripathi said high amines and chlorine content in winter was another interesting aspect, each of which could highlight key sources of pollution.
“Chlorines could be due to burning of solid waste or industries. High amines also come from vehicular traffic. Delhi has overall more finer particles than the rest of the NCR, which needs action in the long run,” said Tripathi.
The research suggested switching to electric vehicles in the long run, along with control over industries and power plants to reduce aerosol formation.