In Delhi-NCR, updated AQI warning system to form backbone of new Grap

The system is called the the Decision Support System (DSS), and has been developed by the Indian Institute of Tropical Meteorology, Pune (IITM) in collaboration with the Union government’s ministry of earth sciences.

The air pollution forecasting model that will inform what degree of pollution control curbs should be in place has an accuracy of 80% and is being improved further this year, scientists involved in the process said, explaining the updates will also bring the ability to assess whether the restrictions are helping.

Traffic in Delhi-NCR. (Parveen Kumar/Hindustan Times)

The Commission for Air Quality Management (CAQM) unveiled the new Graded Response Action Plan on Wednesday, a blueprint of pollution control measures that lay down what activities should be restricted before the air reaches certain thresholds of pollution.

The past version of the plan was activated only when pollution breaches those trigger points, which meant the steps were often inadequate to pre-empt a crisis period.

“We are working on the updated features and we are trying to implement these before the pollution season this year so that it can be put to use. Essentially with this new feature authorities will be able to see that by implementing each restriction under Grap how much is the pollution level getting impacted,” a senior scientist involved in the development of what is known as the Decision Support System (DSS) told HT on the condition of anonymity.

The DSS has been developed by the Indian Institute of Tropical Meteorology, Pune (IITM) in collaboration with the Union government’s ministry of earth sciences in what may be the most sophisticated pollution forecasting model in the country.

The efforts of the system are focussed on Delhi, and it takes into account a host of factors and observations. Among these are what the agency describes as a “state-of-the-science” online chemistry transport model that makes use of an emission source database created by The Energy and Resources Institute for Delhi and 19 of its surrounding districts, as well as readings from pollution monitoring stations dotted all over north India, satellite data of aerosols – or particles in the air – that can be seen through instruments known as spectroradiometers and the number of farm fires that can be seen from space.

These data points are then fed into a model to create projections for the next three, five and ten days.

“Long-range forecasts have low accuracy as compared to the three-five-day forecasts that we send out. We had developed the 10-day forecasts on the request of CPCB so that they get ample time to initiate action to control pollution sources. We have an error margin of around 20% with short-range forecasts, but it is not completely off the mark. For instance, if we predict that the air quality will be in the ‘severe’ level in 100 instances, it has settled in the ‘very poor’ level in 20 cases,” the scientist said.

Data maintained by IITM-Pune showed that the DSS system had an accuracy of nearly 82% for short-range forecasts—for three to five days—and around 60-65% for long-range forecasts, which are issued for the next 10 days.

The accuracy data is for the modelling system’s forecasting for three years—2019, 2020 and 2021. In 2019 and 2020, the DSS was being used on a pilot basis by the Central Pollution Control Board (CPCB), before it was formally launched in 2021.

The scientists also said that an analysis of how these predictions helped government control the forecasts was carried out earlier this year and showed that agencies were able to control pollution levels by 18-22% after inputs.

Anumita Roychowdhury, executive director (research and advocacy), Centre for Science and Environment (CSE), said: “While Grap was formulated as a reactive plan because it is an emergency action plan, there was also a comprehensive action plan that aimed at year-long action to preventive high pollution levels. We have been reiterating time and again that pollution action cannot be restricted to one season and it has to be done throughout the year. Forecasting models give a heads-up to agencies and should be used to preventive extreme pollution episodes.”

Beginning this year, the Grap, split into four sets of curbs, each progressively stricter in step with higher bands of the air quality index. Among the curbs that will come into place if pollution is predicted to worsen beyond the ‘very poor’ AQI of 301 and above are a ban on the use of diesel generators, an embargo on the use of diesel vehicles, including private cars not conforming to the Bharat Stage VI standard, and a restriction on the use of coal-fired ovens.