Smoke rises from a chimney of a garbage processing plant on the outskirts of Chandigarh, December 2011. Photo: Reuters/Ajay Verma.
We observed four lockdown phases between March and May 2020: (a) March 24 to April 14 (21 days); (b) April 15 to May 3 (19 days); (c) May 4 to May 17 (14 days); and (d) May 18 to May 31 (14 days). From June 1, individual states started to ease the restrictions in phases and some states also imposed partial lockdowns depending on the community infection rates.
At the end of each phase, two reports in The Wire Science – this and this – explored the air-quality trends in cities with at least one ambient monitoring station each, for all pollutants responsible for defining India’s official air quality index. (The data is available here.)
The most important lesson from this forced lockdown experiment is the fact that we can achieve “clean air” and national ambient standards. The 2-month period of lockdowns, with the restrictions at the fullest in the first phase and little relaxed in the fourth, demonstrated that the only way to achieve “clean air” is by cutting emissions. There is no scope for short-cuts or silver-bullets in this goal.
Second lesson is that a city-centric or sector-centric approach is not enough. Going forward, looking beyond these COVID times, we must plan to cut emissions at all the sources inside and outside the city limits, in order to maintain sustained reductions. We should also avoid band-aid solutions like smog-towers, mist-cannons and odd-even rules, which only benefit small pockets of a city.
What happened during the lockdown periods across the country?
1. All the offices implemented work-from-home and all the schools, colleges, universities, training institutions, markets, malls, religious centres, and other public spaces were shut – this reduced most of the demand for passenger movement on the roads.
2. All the shops and small-scale industries in the urban and rural areas were shut – with exceptions introduced after for essential food and medicine supply chains.
3. All the construction activities were banned including brick manufacturing – this reduced the dust loading in the hotspots, debris movement, and construction freight movement.
4. All the open waste burning activities were banned – this was possible also due to the fact that movement on the roads and within/outside the residential communities was restricted.
5. All the passenger and public transport movement was stopped – with exceptions for police, press, and medical practitioners and some with special permissions on a need for basis.
6. All the freight movement was stopped on the highways and at the interstate border crossing. This was eased after the first week in response to supply shortages in the cities, mostly for essential goods.
7. Heavy industries (like power plants, refineries, fertilisers, cement, iron and steel, and other ore processing units) limited their operational times and fuel consumption loads, in response to the lower demand.
As the lockdown periods were extended, air quality improved at various degrees, not just in the big cities like Delhi, Mumbai, Kolkata, and Chennai, but across the country.
Airshed management approach
Looking beyond the city limits is critical, especially for a region like the Indo-Gangetic plain, with cities in proximity and feeding each other, not only for commerce but also pollution. My colleagues and I at Urban Emissions evaluated the air quality trends for 60 cities.
We established a baseline emissions inventory for every city at 1-km resolution and for all India at 25-km resolution, using a database compiled from statistics, energy, industrial and environmental departments. We then combined this with local and regional meteorological data through a state-of-the-art chemical transport modelling system to evaluate contributions of different sources inside and outside cities.
For cities in Punjab like Amritsar, Ludhiana, Patiala and Chandigarh, outside contribution is more than 50%. For cities like Chennai, with the sea on one side and mostly agricultural activities on the other, this share is 15%. On average, 30% of the observed PM2.5 pollution in the 60 cities is regional in nature, originating outside city limits.
More contribution means need for more regional and sometimes inter-state collaboration to achieve clean air. Delhi and Mumbai are classic examples of big cities with many satellite settlements. While Mumbai enjoys the luxury of most of its influential regions in the same state, Delhi needs a strong regional coordination with Haryana, Punjab, Uttar Pradesh, and Rajasthan.
This airshed approach is not new for India. We use this concept in various other sectors, but never internalised it for air quality management per se.
The Central Electricity Authority maintains and records information across India in five electricity zones: northern, southern, western, eastern and northeastern. All states within each zone pool their information of demand and supply in real time.
Studies of India’s climate are split into six zones: mountainous north covering the Himalayan ranges, humid subtropical covering most of the Indo-Gangetic plain and the northeast, tropical wet and dry which is most of the Central and East India covering the Deccan plateau, tropical wet which is most of the regions west of the Ghats, arid regions covering the desert and semi-arid regions between the Ghats and plateau. Each of these zones is unique in their land-use and annual precipitation profiles.
Similarly, we divided India into 10 biogeographic zones, 20 water basins and 24 land-use categories. The last category is fragmented with no smooth boundaries to define.
The most interesting and useful approach comes from the India Meteorological Department, with 36 sub-divisions. These are drawn along the district boundaries with similar temperature, precipitation, and landcover classification. The daily reports for each of these sub-divisions range from short-term (1-2 days) dust, thunder, lightning, and storm alerts to long-term (10 days to a month) meteorological predictions to help the local farmers.
An ideal set of airsheds necessary to define air quality management zones lies somewhere between the 10 biogeographic zones to 36 meteorological sub-divisions.
To take the lessons from the lockdown forward, we must adopt an airshed approach to strengthen the state and regional efforts. This will benefit all cities – like trends observed during the lockdowns, where pollution reductions in any city are complemented with similar reductions in the region (beyond the airshed) to reach and sustain the national ambient standards.