Local sources behind bulk of pre-Diwali pollution in Delhi: Report

One of the key findings of the study was that vehicles are the highest contributors to local air pollution sources in Delhi — it was more than half of the pollution coming from other local sources such as industry, construction, road waste, etc.

During the pre-winter phase, the overall contribution of farm fires has only been 4.4%. “So far this year, farm fires have had a minimal impact on Delhi’s air quality, with their contribution to PM 2.5 levels remaining below 1% until October 20… Unlike previous years, smoke from stubble fires has not overwhelmed the region’s air quality yet,” said the study.

“Usually, every year, the contribution of farm fires to Delhi’s air quality during this first phase of winter is considered the biggest problem, detracting attention from local sources of air pollution. But this year, the air quality of Delhi turned from ‘poor’ to ‘very poor’ even when, for the most part of this phase, the contribution of farm fires has remained less than 1-3%, reaching up to 8-16% only on two days. This exposes the problem of higher contribution of local air pollution sources,” said Anumita Roychowdhury, executive director, research and advocacy, at CSE.

The other key takeaway from the study was the status of 13 pollution hotspots — except Mundka and Bawana which saw an improvement of 12% and 7%, the rest saw a spike in PM 2.5 levels compared to 2023.

Despite this progress, Bawana still recorded the second-highest PM 2.5 levels from October 21 to 28 with an average of 201 µg/m³. Burari Crossing led the list, averaging the highest PM 2.5 concentration at 204 µg/m³.

The study also noted that Nehru Nagar and Vivek Vihar have emerged as new pollution hotspots, each averaging 92 µg/m³ in PM2.5 concentration.  On an annual average, Anand Vihar is the most polluted hotspot in 2024, with a PM 2.5 level of 111 µg/m³, followed by Jahangirpuri at 102.

Roychowdhury said, “It is clear that while action on farm fire needs to be more aggressive and impactful to eliminate the problem, the seasonal episodic pollution cannot continue to mask and hide the significant contribution of local pollution sources and sources from the surrounding regions. Clean air benchmarks cannot be met and sustained throughout the year without stringent and upscaled action targeting the key sources of pollution including vehicles, industry, solid fuels, waste burning and construction, among others. This immediately requires an action taken report to identify the key gaps in action and the strategy to address this.”

Further, experts at CSE said pollution has been aggravated by the escalation in traffic congestion.

A strong co-relation between vehicles and hourly changes in NOx levels with congestion in the city was also found when the CSE analysed hourly travel time data for 25 road stretches in Delhi from September 15 to October 29 using Google Maps API.

Congestion was highest on the weekend before Diwali (October 27). “During this time, the hourly concentration of NO2 was notably elevated, peaking at 61 µg/m³ in the morning when traffic speed averaged 31 km/h, and reaching 75 µg/m³ in the evening with a reduced traffic speed of 21 km/h. Notably, even at midnight, the concentration of NO2 remained elevated at 68 µg/m³,” stated the analysis.