Winter’s knocking, but Delhi’s real smog culprit might surprise you

Delhi pollution

As Delhi braces for its annual winter air quality crisis, a key forecasting tool has been reactivated. The findings from its initial data present a surprising picture of the city’s early-season pollution sources.

The Decision Support System (DSS) for Air Quality Management is now operational for the winter, as reported by The Indian Express. Developed by the Indian Institute of Tropical Meteorology (IITM) in Pune, the system tracks and estimates the daily contribution of various pollution sources.

It uses a numerical model to pinpoint the origins of harmful particulate matter (PM2.5 and PM10). This helps project the potential impact of measures designed to curb emissions.

The first available data, from Sunday, reveals that farm fires are not yet a significant factor. The contribution from stubble burning was a minimal 0.22%. Instead, the transport sector emerged as the single largest contributor to Delhi’s PM2.5 levels. It accounted for 16.96% of the pollution.

Other notable sources included residential emissions at 4.28% and industries at 3.11%. This data, cited by The Indian Express, is based on satellite fire counts up to Saturday evening.

Despite its utility, the DSS is not without its critics. Its current estimates rely on an emissions inventory formulated in 2021. An IITM official confirmed that this could affect the precision of its source-wise breakdown.

The system was temporarily suspended last year by the Commission for Air Quality Management (CAQM) over data accuracy concerns. The CAQM is the statutory body tasked with managing air quality in the capital region.

Nevertheless, the DSS remains the only operational framework for identifying source-wise pollution. A planned real-time source apportionment study by the Delhi Pollution Control Committee (DPCC) has not yet resumed after being halted last year.

The IITM portal acknowledges the need for "the latest emission fields" for more accurate estimations. A new inventory is in preparation and will be incorporated upon completion.

The DSS generates forecasts and decision-support information for the next five days. According to IITM, it provides quantitative data on several key areas. It shows how much Delhi’s own emissions and those from 19 surrounding districts affect its air quality. It also breaks down the contribution from eight different sectors within the city.

Furthermore, it estimates the impact of biomass burning in neighbouring states. Finally, it models the effects of potential interventions during severe air quality episodes.

A study by the Council on Energy, Environment and Water (CEEW) earlier this year praised Delhi’s Air Quality Early Warning System. It successfully predicted the vast majority of severe air quality episodes in the last two winters. However, the study noted a significant limitation. The DSS currently operates only in winter. For full effectiveness, the CEEW argued, it should run year-round and incorporate more modelling scenarios.

The model’s forecasts for the next three days use climatological data on fires and emissions. It has also shown an ability to retrospectively refine its analysis, such as revising stubble-burning estimates to account for firecracker emissions from wedding celebrations.