Vehicles are the biggest contributor among the local sources in Delhi

  • Analyses real time source contribution data generated by Indian Institute of Tropical Meteorology -- shows among the local sources, vehicles have contributed more than half of Delhi’s particulate pollution between October 24-November 8
  • Other sources (in descending order):household sources, industries, construction, waste burning and road dust
  • During November 2-6 (Diwali period), contribution from other NCR districts was substantially high;this reduced duringthe smog episode post-Diwali-- share of Delhi’s contribution and biomass-burning increased
  • Contribution of biomass-burning until November 3 remained low – was the lowest in last four years. But it increased significantly from November 5
  • During this phase,traffic speed plummeted and congestion bounced back to pre-pandemic levels
  • While Delhi needs to speed up action on all key sources of pollution, it requires urgent action to scale up integrated public transport systems, walking and cycling infrastructure, and city-wide parking area management plans to restrain vehicle use
  • In absence of this reform, Delhi is unable to enforce emergency action to control traffic volumes during smog episodes. Vehicle numbers are explosive at 1.32 crore  
  • To meet clean air target integrated multi-sector regional action plan will have to be implemented across NCR and beyond with strong compliance strategy.

Find the complete CSE analysis click here

New Delhi, November 11, 2021:Vehicles have emerged as the biggest contributor to particulate pollution in Delhi – their real time share has increased to more than 50 per cent during the early phase of winter (October 24-November 8, 2021), says another new analysis from Centre for Science and Environment (CSE) released here today. CSE had released an analysis yesterday of Delhi-NCR’s smog scenario
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Today’s CSE study has analysed the real time data on source contribution done by the Decision Support System for Air Quality Management of the Indian Institute of Tropical Meteorology (IITM) in Pune. 

The other contributors -- in descending order -- are household pollution, industries, construction sector, solid waste, and road dust. 

An additional CSE analysis of the trends in traffic speed in the city –a measure of congestion -- during early winter (October 27-November 6, 2021) on 15 road stretches of key roads show that traffic congestion is back to pre-pandemic times and correlates with the pollution peaks. 

“Clearly, after the closure of all coal-based power plants, expansion of natural gas usage in industry and controls on dirty fuels, vehicles have emerged as the biggest real time contributor among the local sources of winter pollution in Delhi this year. Action on transportation has to gather strong momentum. At the same time, action on waste management, clean energy access in households,and dust control must be speeded up,” says Anumita Roychowdhury, executive director-research and advocacy, CSE. 

Key highlights 

Vehicles dominate real time source contribution to Delhi’s particulate pollution: CSE has analysed the real time data on the relative contribution of different pollution sources to Delhi’s air quality.It has accessed data forevery alternate hour for the period October 24-November 8. The pollution sources include transport, industry, construction, waste burning, energy, residential sources, road dust and other groups of sources. 

The analysis clearly shows vehicles’ contribution is half or more. This is followed by household pollution that has ranged between 12.5-13.5 per cent, industry (9.9-13.7 per cent), construction (6.7-7.9 per cent), waste burning and road dust (each varied between 4.6-4.9 per cent and 3.6-4.1 per cent, respectively). This indicative trend is based on the trendsvisible every alternate hour during 24 hoursof the study period. 

The Decision Support System (DSS) of IITM is part of the 'Air Quality Early Warning System' and provides information on the potential emission sources to air quality in Delhi.This uses an online chemistry transport model 'Weather Research and Forecasting with Chemistry' (WRF-Chem); its modelling uses available emissions inventory for Delhi and the surrounding 19 districts, as well as the PM2.5 data from the Central Pollution Control Board (CPCB) monitoring stations and satellite imaging of pollution. This provides quantitative information on contribution of emissions from Delhi’s own sources and the 19 districts in the National Capital Region (NCR),andalso the contribution from biomass-burning in neighbouring states. This can also estimate the effects of possible emission source-level interventions on the airquality event in Delhi. 

Contribution of outside sources and Delhi’s own sources varies during the day and overtime: The DSS system also tracks data from sources outside Delhi – 19 districts in the NCR as well as biomass burning in neighbouring states. During November 2-6, the contribution of NCR dominated in the initial phase going upto 70-80 per cent, but its share declinedduring the smog episode post-Diwali when the relative contribution of Delhi’s own sources increased. Similarly, the contribution of biomass burning from other states remained low in the initial pre-Diwali phase but peaked post Diwali. Clearly, the calm conditions during smog episode post Diwali has reduced intrusion of cross boundary movement from NCR and enhanced the share of local pollution in Delhi. On the other hand, the long range transport wind brought more pollution from biomass burning from neighbouring states. 

Also,during the day it has been noticed that the overall contribution of Delhi’s own sources increase normally during evening hours and lasts until early morning hours (7:30 pm to 9:30 am). 

Congestion impacts during early winter: CSE has also carried out a rapid diagnostic assessment of the changing travel speeds during October 27-November 6, 2021. It has analysed the Google Maps data for 15 major roads that include the MB Road (South), Outer Ring Road (South), Outer Ring Road (North-West), Ring Road (South), Ring Road (North-West), Ring Road (North-East), MG Road (East), Mathura Road (East), ITO Road, Sri Aurbindo Marg (South), Central Delhi, Lal Bahadur Shastri Marg (South), Guru Ravidas Marg (South), and GT Karnal Road 1 and 2. 

Length of the roads was identified to be representative of the geographical spread as well as the larger mobility pattern of Delhi. The travel time from origin to destination was noted for every hour from 8 AM to 10 PM for the period, which was later converted into speed in km per hour. The data was further analysed for the peak hours (from 9 AM to 11 AM in the morning and 5 PM to 7 PM in the evening) and for the rest of off-peak hours. 

Congestion returned to close to pre-Covidtimes: Travel speed is only indicative of the level of congestion on roads; this is not to build a case for high-speed traffic that can compromise safety and impede other forms of mobility like walking and cycling and use of public transport. The overall traffic speed that had improved dramatically during the hard lockdown phases in 2020,has gradually increased with the reopening of the economy.The mean travel speed is 26 kmph; in peak hours it is 23 kmph.During off-peak hours, it has been 32 kmph. The speed during the same period in 2019 was 23 kmph in peak hour. Thus, traffic build-up has returned back to pre-Covid levels. 

Change in peak and off-peak hours: Normally, in traffic studies, peak traffic flow is usually observed during morning from 8 AM to 11 AM, and in the evening from 5 PM to 8 PM. Off-peak period is during 11 AM to 2 PM. The traffic during morning peak is comparatively lower than the evening peak. The main peak builds up from 6 PM to 8 PM in the evening. On Diwali day and the following weekend, the overall traffic in the city was observed to be relatively lower. When the traffic scenarios for specific days were compared, it was observed that congestion build-up was highest on November 2. Diwali day – being a holiday -- saw the least traffic build-up. 

The congestion-pollution link: The traffic peaks also influence the hourly build-up of pollution during the day. While PM2.5 is influenced by several other factors, nitrogen dioxide (NO2) is more closely related to traffic trends. During the study period, NO2levels show a strong correlation with congestion. The levels increase when traffic speedsgo down. 

Focus on the solutions needed

As action progresses in different sectors it is changing the relative positions of different pollution sources in the city. This, therefore, demands more nuanced and dynamic response to refine the action strategy. After the closure of coal-based power plants, expansion of natural gas in industry, clean fuel policy among others, the relative contribution of vehicles has increased significantly. 

Vehicle numbers are explosive in Delhi -- 1.32 crore registered vehicles according to the VAHAN database. While accelerating action on all key sources of pollution,Delhiurgently needs to scale up integrated public transport systems, walking and cycling infrastructure, city-wide parking area management plans,and low emissions zones to restrain vehicle use and meet the electrification target of 25 per cent by 2024. Without these reforms,Delhi will not be able to enforce emergency measures to control vehicle numberson road during smog episodes. 

To meet the air quality target in Delhi and NCR, air pollution action will have to be scaled up across  NCR region and beyond. Integrated multi-sector regional plan will have to be implemented with strong compliance strategy in all states of NCR and beyond. 

For more information, contact Sukanya Nair,, 8816818864.



Associated graphs of this CSE analysis
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Press Release
November 10, 2021
Season’s first smog episode has hit Delhi-NCR, says new CSE assessment