Vehicle emissions fell to 5% in early lockdown: Study
Contribution of vehicular emissions to Delhi’s PM 2.5 concentrations reduced from 19% during the pre-lockdown period to only 5% during the lockdown period between March 25 and 17. It again increased to 15% during phase 3 of the lockdown in May, a new analysis has shown.
The impact of the nationwide lockdown to halt spread of Covid-19 starting March 25 was visible on Delhi’s air quality but a source apportionment study commissioned by Central Pollution Control Board (CPCB) to IIT Kanpur and IIT Delhi has revealed what exactly changed during the various phases of lockdown until May.
The study was referred to by CPCB in its report titled “Impact of Lockdown on Ambient Air Quality” released on Wednesday.
Vehicular emissions, local coal and waste burning and urban organic aerosols (generated from urban sources) reduced sharply from the pre-lockdown phase into lockdown phase and were found to be steadily rising again with increasing relaxations under the Centre’s Unlock plan.
The share of biomass burning reduced 21% in the pre-lockdown period to 17% during the initial lockdown phase until April 17. The share of contribution from power plants increased from 10% before lockdown to 25% in the lockdown period. This could be because of decrease in contribution from other sources, the report said.
The source apportionment study was conducted in four phases--pre-lockdown (February 19 to March 24), lockdown phase-1 (March 25 to April 17), lockdown phase-2 (April 18 to May 3) and phase-3 (May 4 to May 18). Maximum restrictions had been imposed during the first phase of lockdown.
It was also observed that contribution from vehicular emissions in PM2.5 levels were found to be higher (14%) only in the pre-lockdown phase, while for all consequent phases the factor was found to contribute only in trace amounts. Similarly, both the coal combustion and waste incineration sources decreased steadily during lockdown months.
Black carbon which is primarily contributed from biomass burning and traffic emissions in total PM2.5 composition dropped from 12% during pre-lockdown period to 6-8% during lockdown phases.
Secondary chloride remained unaffected by the lockdown. “This is a research question as to why secondary chloride concentrations didn’t change. Secondary chloride is generated due to various other chemical compounds which may have chloride in them interacting with each other. We are still studying this,” said SN Tripathi, head, civil engineering department, IIT-Kanpur.
Air quality in Delhi had improved compared to 2019 even during the pre-lockdown period in 2020. This may be due to meteorological conditions as well as the fact that a few restrictions such as those on cinema halls, schools, colleges, etc. were already in place during the first half of March, the CPCB report said.
PM2.5 (fine, respirable pollution particles) levels reduced by 24% during the pre-lockdown phase, it further reduced by almost 50% during both lockdown phases as compared to levels observed during 2019. PM10 (coarse pollution particles) reduced by a massive 60%, with nitrogen dioxide (NO2) levels falling by 64%, benzene by 62% and sulphur dioxide (SO2) by 35%, during the second phase of lockdown as compared to levels in the same time period in 2019.
“Real time source apportionment shows us the immediate effect of taking action against pollution sources. It can be a very important tool for decision making because it also shows how toxicity of emissions reduces with stopping of certain emissions and hence having health benefits,” said Anumita Roychowdhury, executive director, Centre for Science and Environment.