Passengers hang outside of a train under heavy smog in New Delhi on Tuesday. (Express Photo by Praveen Khanna)
Nov 19, 2024 22:44 IST First published on: Nov 19, 2024 at 20:44 IST
I remember writing about “a green blueprint” (‘COP & the new abnormal’, IE, December 8, 2023) around this time last year, when COP28 was underway in Dubai, pointing out that any strategy to combat air pollution must not only address immediate concerns but also have a long-term, sustainable approach based on science. Resource frameworks for such an approach must look at “airsheds”, not political or regional boundaries. As COP29 enters its second week in Baku, and global health experts are urging countries to move away from fossil fuel dependence, several northern India cities are experiencing record-breaking “severe-plus” air quality.
Worsening air quality in winter is not a new phenomenon. This year, as October and the first week of November passed without extreme pollution, many, including the authorities, rejoiced. Then, the second week of November hit hard. Toxic particulate matter engulfed most of northern India. New Delhi is covered in thick smog. The most toxic PM2.5 crossed more than 500ug/m3 and visibility fell sharply. To understand the severity, an AQI of 400 (severe) is equal to only 250ug/m3. Given that the official stubble-burning numbers, mainly driven by NASA’s satellite monitoring data, dropped significantly this season (more than 70-80 per cent), this surprised even experts. Most forecasting models also failed to predict this peak. It surprised me too, until I analysed the vertical slice of my air quality chemical transport model. After all, typical winter conditions linked to extreme air stagnation had still not set in.
There are two salient points in this regard. One, if weather conditions and wind levels are favourable for an intrusion from Punjab-Haryana and adjoining areas (around 500m to 1500m above the surface) and they are fast enough to recede over NCT, then a threshold of even 400-500 fires, combined with stagnation conditions (no dispersion) can have an adverse local impact. Two, models show a thick blanket at 500m instead of clear skies. This is just above the boundary layer that separates the lower atmosphere from the inversion layer above. This blanket descends as temperatures fall at night and is largely responsible for elevated pollution levels. However, in the week leading up to November 18, pollution shot up from sunrise until afternoon when the boundary layer breaks and rises. That is because the ominous blanket of polluted air at 500m made a downward intrusion and worsened air quality. This suggests that there is a major source of external pollution as local emissions will not rise so sharply. A combination of fossil fuels, domestic emissions and this unknown source have played havoc with Delhi’s air.
Given the reality of climate change, there are many factors at play and they demand multidisciplinary, multisectoral solutions. We are witnessing many unusual events — the warmest October on record, uncertainty around the onset of La Nina and more. La Nina, associated with a good monsoon, was initially expected by June. We have witnessed a good monsoon – and LaNina is yet to set in properly.
La Nina is important to the air quality discussion because it is associated with better wind circulation – winter 2022 was a case in point.
The air we breathe is a choice we make as a society at the expense of our health and that of young children. The air quality issue this time has thrown up more questions than answers. We need to ensure greater transparency on such an important matter. The greatest confusion was that some credible private agencies often show AQI readings of more than 1,000-1,500 while the official figure never goes beyond 500, using the same data from the authorities. This is because India’s guidelines for converting mass concentration of pollutants to the AQI figures are based on its own “breakpoint”, which are far less stringent than the WHO-prescribed guidelines. Breakpoint is the threshold level from where the AQI readings go from one category to another. Our AQI is set based on our epidemiological data and susceptibility studies that keep the Indian environment in mind. This would be fine, except for the discomfort of setting a cap at 500 AQI, regardless of how many times the concentrations exceed that level.
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Another serious issue emerged when a senior research scientist from NASA claimed that farmers in north-west India have changed the time for stubble burning by 3-4 hours to avoid detection by the MODIS instrument on board the Terra and Aqua satellites that pass over this area. These satellites are not geostationary – they only pass the areas twice in 24 hours. This conclusion was based on images from the Korean geostationary satellite (GEO -KOMPSAT 2A) which, it was claimed, showed localised puffs/clouds of smoke in the late afternoon. I do not wish to make any judgment on the issue at this stage. However, to understand the truth about the timing shift scientifically, we should analyse and process the images of our Indian geostationary satellites (INSAT-3D/3DR), which provide continuous coverage (every 15–30 minutes).
A significant amount of work using ISRO satellites is going on in India for various applications. Unfortunately, not much attention is paid to air quality in this regard. This is one reason our official fire count data is dependent on NASA satellites. We have the capability of becoming independent in this area and may even launch a new high-resolution satellite. But this requires a push. The Delhi air quality crisis is a reminder to frame strategies by scientifically integrating air quality and climate factors and prioritising health-centric measures. This can best be realised by a resource framework, as envisaged recently in a stakeholder meeting convened by the office of the Principal Scientific Advisor to the Government of India.
The writer is Ashutosh Mukherjee Chair Professor, National Institute of Advanced Studies, Indian Institute of Science (IISc) Campus
