New Delhi: As Delhi and the National Capital Region brace for the upcoming winter, it remains to be seen if the seasonal average of PM2.5 during winter -- that had improved during the pandemic but had stagnated post-pandemic -- will further bend or increase. This winter season is also starting from a much cleaner benchmark due to rains in September and October.

Centre for Science and Environment’s Urban Lab has released its winter pollution assessment – the objective, says Anumita Roychowdhury, executive director of research and advocacy, has been “to understand the trend and the starting line of the onset of the winter pollution season or pre-winter levels in this region. This would also capture the longer term context of seasonal variation and annual trends in particulate pollution.”

This is the first analysis of the third edition of Urban Lab’s Air Quality Tracker Initiative which was started in 2020-21 winter to study the impact of the pandemic lockdown on the air quality of Delhi-NCR.

“The intensity of winter pollution and severity of smog episodes will depend on the effectiveness of the long-term multi-sector action so far in the entire region of Delhi and NCR and also on the enforceability of the short-term emergency action. Only the effectiveness of the air pollution control measures targeting all key sources will determine if the winter pollution trend that had stabilized post-pandemic, will continue to hold and improve or worsen further,” says Roychowdhury.

“The onset of the winter has been much cleaner this year due to the rains. But the intensity of the early winter pollution will depend a lot on the trend in the crop fires and also the impact of Diwali. Though Diwali happened during the warmer part of the early winter, prolonged rains can delay and lead to concentrated burning later compounding the problem,” says Avikal Somvanshi, an analytic expert at the Urban Lab.  

This is an assessment of annual and seasonal trends in PM2.5 concentration for the period 1 January 2015 to 17 October 2022. This captures seven successive winter seasons and pre-winter trends in Delhi and the National Capital Region. This analysis is based on the real-time data available from the current working air quality monitoring stations in Delhi-NCR. A huge volume of data points has been cleaned and data gaps have been addressed based on the USEPA method for this analysis.

This analysis covers 81 continuous ambient air quality monitoring stations spread across cities of Delhi-NCR. Meteorological data for the analysis is sourced from the Palam weather station of the India Meteorological Department. Fire count data is sourced from NASA’s Fire Information for Resource Management System, specifically Moderate Resolution Imaging Spectroradiometer and Visible Infrared Imaging Radiometer Suite product is used. The estimate of the contribution of farm stubble fire smoke to Delhi’s air quality is sourced from the Ministry of Earth Science’s System of Air Quality and Weather Forecasting and Research.