IIT-K study reveals biomass emissions cause high pollution in Delhi during night

A collaborative study led by Indian Institute of Technology (IIT), Kanpur has found that the high amount of particulate pollution in Delhi during nightly hours was caused by biomass burning emissions. The study published in Nature Geoscience journal is led by IIT Kanpur and is contributed by Physical Research Laboratory (PRL), IIT Delhi, Central Pollution Control Board (CPCB), Paul Scherrer Institute (PSI) Switzerland and University Helsinki, Finland. The research paper is co-authored by Suneeti Mishra and Prof Sachchidanand Tripathi, from the Department of Civil Engineering, IIT Kanpur.

According to an IIT-K release, Delhi often experiences high amount of particulate pollution also termed as haze. However exact reasons behind their formation were hitherto unknown. The exhaustive research unearthed the reason behind the severe haze events experienced during winters in Delhi which is one of the world's most-populated cities.

Prof Sachchidanand Tripathi, from IIT Kanpur who was the Principal Investigator in the study said, "The uncontrolled biomass burning for residential heating and cooking in the Indo-Gangetic plain gives rise to ultrafine particles, affecting the health of 5 per cent of the world's population and impacting the regional climate. Regulating the uncontrolled biomass-combustion emissions may help inhibit nocturnal haze formation and improve health. The study becomes important as air pollution is responsible for 18 per cent of the total annual premature deaths in India."

This study was designed for Delhi during the winter months of 2019 where aerosol size distribution and molecular composition of ambient aerosols and gases were measured. The measurements helped calculate growth of aerosols during night time along with the sources of aerosols and also the sources of gases.

The study found that very high growth rates (tens of nano meter per hour) of aerosols especially for those smaller than 100 nano meters (nano particles) have been found in unfavourable new particle formation conditions compared to other places in the world, leading to haze formation in a span of few hours during extreme pollution events. The molecular information about aerosols clearly showed that organic vapours from biomass burning contributed to the growth of nano particles. It was also found that the composition of particles whose sizes were greater than 100 nano meter particles composition were dominated by ammonium and chloride species.

Simultaneously, measurements of gases at molecular level showed that the biomass burning sources were their chief source which has preferential condensation on nano particles. Thermodynamic modelling of gaseous partitioning confirmed the observational findings. The study points out that the reduction of uncontrolled combustion, especially during conducive weather conditions, may limit the amount of supersaturated vapours available for nanoparticle growth and hence may be an effective strategy for the mitigation of nocturnal particulate number during haze in Delhi.