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Behind air crisis: High baseline pollution, multiplicity of factors

Nov 22, 2024 08:48 AM IST

Delhi's pollution remains severe, with AQI at 441. Reducing sources won't suffice; a unified effort beyond politics is crucial for improvement.

New Delhi Both pollution and the political blame game around it have become toxic cliches in Delhi. What would it take to actually bring down pollution in Delhi to permissible levels? According to the National Ambient Air Quality Standards (NAAQS) this would work out to an AQI (Air Quality Index) reading of up to 100.

Vehicles ply on a road as the sky is enveloped with smog after Delhi's air quality worsened due to air pollution, in New Delhi, India, on Wednesday. (REUTERS) PREMIUM
Vehicles ply on a road as the sky is enveloped with smog after Delhi's air quality worsened due to air pollution, in New Delhi, India, on Wednesday. (REUTERS)

Building a quantitative correspondence between pollution levels and its causes requires the use of a modelling exercise. For Delhi, these estimates are given by the Decision Support System for Air Quality Management in Delhi (DSS). DSS calculates the contribution by feeding a model with data on different sources of pollution, such as the number of fires recorded in Punjab and Haryana, the air quality in Delhi’s neighbouring districts, and other satellite-based indicators of pollution (and as we learnt on Tuesday, DSS also uses some off-the-wall measures, such as the number of weddings in Delhi, and assuming that fireworks will be used in each). These factors are then made to interact with meteorological factors such as temperature, humidity, wind direction and speed to generate an estimate of air quality and the contribution of different factors.

If one were to believe the DSS numbers, what would it take to bring Delhi’s pollution levels within NAAQS levels?

On November 17 (the AQI on the day was 441 and it is the latest data available from the DSS), even halving each source of pollution would not bring the AQI down to permissible standards, an HT analysis of DSS data shows.

Read more: 50% Delhi government employees to work from home due to air pollution, announces Gopal Rai

DSS has 29 sources of pollution in its model. The biggest contributor to Delhi’s PM2.5 concentration on November 17 was the “Others” category, which contributed 29.4%. Completely removing the pollution from this source would bring down Delhi’s AQI by a big amount – from 441 to 372. However, an AQI of 372 is also in the “very poor” category, and not very far from the “severe” category, which begins at 401. Similarly, the second and third biggest contributors to Delhi’s air pollution on November 17 were Delhi’s own transport sector (17.2%) and stubble-burning in neighbouring states (13.1%). Just stopping all transport in Delhi on the day would bring down AQI to 401 and just dousing all the fires in Punjab and Haryana would bring down the AQI to 411, both of which would still land Delhi in the “severe” category. In fact, even if all sources were halved, Delhi’s AQI on November 17 would only be 323.

To be sure, this analysis needs to be read with the fact that AQI levels show a diminishing relationship with rise in air pollution levels and therefore reducing pollution from very high to high levels would have muted impact on AQI reduction.

And to be sure, this analysis is based on DSS, which is likely inaccurate or inadequate or both.

Still, the fact remains that bringing down pollution in Delhi needs a more concerted effort than the ongoing blame game between political parties.

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