IMD’s new improved air quality models capture air pollution spike in Delhi

Air quality forecast models for Delhi — and the rest of India — have been enhanced, enabling more granular predictions this year with the identification of pollution hotspots in Delhi, according to the India Meteorological Department (IMD).

October 15 forecasts for the country show PM 2.5 concentrations ranging from 100 to 200 micrograms per cubic metre, much above the level deemed to be safe, in many parts of northwest India and the Indo-Gangetic Plains. The 24-hour safe standard for PM 2.5, one of the main air pollutants, is 60 micrograms per cubic metres.

When it comes to PM 2.5 in Delhi, the entire city seems to be enveloped by concentrations of over 250 micrograms per cubic metres, according to IMD’s ENFUSER air quality forecast model launched on Wednesday. But sulphur dioxide hotspots can be easily identified in the model as the concentrations are variable in different parts of the city.

Also Read: Delhi’s AQI improves marginally but remains in ‘poor’ zone

“Forecasting is a very important part of emergency action. It helps in doing proactive planning. If there is good science, it certainly helps you refine your strategy. The graded response action plan (GRAP) which is currently in force will greatly benefit from it. If there is hotspot-based data, even vulnerable populations whose health could be impacted by high air pollution can be identified,” said Anumita Roy Chowdhury, executive director, Centre for Science and Environment.

GRAP, is a set of curbs triggered in phases as the air quality deteriorates, which is typical of the October-November period. Farm fires in neighbouring states and cooling weather typically combine at this time of the year to blanket the region in smoke.

The air quality forecast model, System for Integrated Modelling of Atmospheric Composition (SILAM), meant for the entire country, has been improved by implementing global emission inventories for coarse and fine particulate matter at 10 km resolution.

“Earlier we had 50 km resolution. Plus, we have also added land cover and land use data to obtain a better forecast,” explained Vijay Soni, a scientist at the air pollution division of IMD.

A very high-resolution city scale model has been operationalised for Delhi to identify the air pollution hotspots and pollution up to the street level. The model uses air quality observations, the road network, buildings, land use information, high resolution satellite maps and population data to generate forecasts.

The results are being evaluated to capture pollution hotspots in Delhi, Soni said.

Now the air quality warning system will also provide forecasts for Lucknow, Kanpur and Varanasi at 2 km resolution. “For the Delhi model, we are using real time air quality data from ground monitors, traffic congestion data, road network data etc to identify hotspots. We will be able to share this information in our bulletins also,” he added.

Also Read: Choking NCR districts: Haryana gets into action after EPCA highlights violations leading to pollution

The spike in Delhi’s current air pollution levels is being attributed to calm conditions in the morning and evening hours and variable winds during the day. Widespread stubble fires are seen on satellite images from both Punjab and Haryana.

“Whenever the wind direction is changing to north-westerly, the impact of stubble fires can be felt in Delhi. Plus, there is no dispersion of pollutants due to calm conditions,” explained Soni.

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