Indian cities, especially Delhi-National Capital Region (NCR) and the other major cities in North India are in the middle of an air quality emergency, with several air quality monitoring stations in Delhi-NCR registering above 999 in the Air Quality Index. This was no surprise though — extremely high levels of air pollution have become the norm around this time of the year across Northern India. As winter approaches, Delhi braces itself for yet another period of toxic smog. With worsening air quality, authorities are springing into action to take short-term measures to ensure air quality doesn’t reach emergency levels. To address air quality for the long term, the national government has launched a National Clean Air Programme, which aims to reduce particulate matter (PM) levels by 30 percent in 5 years.
Air pollution is taking a heavy toll on the health of Indians. A 2018 WHO study finds that indoor and outdoor air pollution resulted in the deaths of nearly 6,00,000 children under the age of five in 2016. Of these, an estimated 101,788 child deaths were in India. A 2017 Lancet Commission study found that ambient air pollution causes a staggering 1.09 million deaths each year in India. A 2017 tool finds that residents of the cities in India’s Indo-Gangetic Plain, home to over 300 million individuals, may lose up to 7 years of life to the toxic health effects of air pollution. A September 2019 study found that air pollution is directly affecting unborn children in the womb.
The state of air quality in Delhi-NCR in 2019
In 2019, Delhi has had a relatively good summer in terms of its air quality. According to government data, the annual air pollution levels in Delhi have reduced by 25 percent between 2014 and 2018. While the data to prove this is contested, the following images of the Delhi sky definitely indicate that the air quality in Delhi was relatively satisfactory till early October this year:
Image of sunset from the same spot, October 22, 2019 (above) and October 31, 2019 (below).
However, with the onset of winter and around the time of Diwali, the regions begin to experience the worst of the air pollution. This is attributable to a combination of meteorological conditions and seasonal episodic sources of pollution which add to the ongoing emissions by sources of pollution – vehicular emissions, industrial and power plant emissions, dust from construction and demolition activities, diesel generator sets, biomass and waste burning as well as other sources.
Meteorology plays an important role. Delhi and much of North India have a winter inversion layer that traps pollution, much like Los Angeles’ summer inversion layer. Low wind speeds prevent the dispersion of pollutants. The temperature inversion layer results in trapping of pollutants further causing higher pollution concentrations. The period from mid-September onwards, Delhi experiences a drop-in temperatures and wind speeds, further reducing dispersion of pollutants and increase in ambient pollutant concentrations.
During this time of year in particular, a significant proportion of Delhi’s air quality woes is from the long-range transport of emissions from crop stubble burning by farmers in the states of Punjab, Haryana and Uttar Pradesh. Soon after the harvesting of the monsoon crop, mid-October – mid-November, an estimated 20 million tonnes of paddy stubble is burned in the northern states of Punjab, Haryana and Western Uttar Pradesh. This coincides with the change in the meteorological conditions, and adds to the pollution concentrations in the region.
Post-Diwali scenario (October 27 onwards)
The ratio of PM2.5 to PM10 indicates the nature of the source of emissions. PM2.5 can attributed to sources of emissions that involve high temperature combustion, such as vehicular engines, industrial boilers, diesel gensets and fireworks, as well as secondary particulate formation. PM10 is usually attributed to sources of emissions including naturally occurring dust, construction and demolition and relatively lower temperatures of combustion, including biomass burning in the form of paddy stubble. A higher ratio indicates a higher share of the former set of sources, while a lower ratio indicates that the latter set of sources is contributing more to air pollution. The normal ratio is around 50 percent for the Delhi-NCR region. NRDC’s analysis looked at this ratio for the period between 0000 hours on October 27 and 0000 hrs on November 4, 2019. The data used was CPCB’s hourly concentration data for about 70 CAAQMS stations in NCR.
Diwali was on October 27-28. By the day after Diwali, the air quality in Delhi-NCR plummeted from the ‘Very Poor’ category to the ‘Severe’ category. The PM2.5-PM10 ratio during this period increased nearly 36 percent, from 0.5160 at midnight of October 27 to a peak of 0.7008 by 4 pm on October 28, indicating that the extensive use of fireworks in the city was a definite factor in this rise in pollution levels.
Within a period of 48 hours of Diwali, the contribution of such crop residue burning increased dramatically. According to the SAFAR programme of the Ministry of Earth Science’s Indian Institute of Tropical Meteorology-Pune, the contribution of crop residue burning increased from 4 percent on October 25 to an estimated 44 percent on October 31. The drop in the PM2.5-PM10 ratio also corroborates this, with the ratio dropping 15 percent from 0.7008 to 0.5978 by 3 pm on October 31. However, while the sources of emissions changed, the total pollutant concentrations in the Delhi-NCR region spiked sharply, with PM2.5 average concentrations nearly touching a peak of 400 µg/m3 by November 1, plummeting further into the “Severe Plus” category. By November 2, the contribution of crop residue burning reduced further, to 17 percent.
On November 2, the city experienced very light drizzles in some places, along with a drop in windspeeds. While initially this resulted in a drop-in air pollution concentration back to the “Severe” category of air quality, this relief was short-lived. The average concentration of PM2.5 increased by nearly 300 µg/m3, or about 120 percent, within a 24-hour time period. By the evening of November 3, PM2.5 average concentrations were touching the season’s highest levels – 550 µg/m3, with the government issuing a city-wide Air Quality Emergency as well a health advisory to protect its citizen from exposure to toxic levels of air pollution.
In the past, rainfall has always been a factor to reduce air pollution by suppressing particulate matter. Further, given a drastic drop of the contribution from crop reside burning, the expectation was that rainfall on November 2 would lead to an improvement in the air quality. However, the situation on the ground is quite to the contrary.
Our analysis shows that the PM2.5-PM10 ratio has increased rapidly from 0.6104 at 4 pm on November 2 to 0.8672 at 2 am on November 4 and it continues to increase. Such a rapid deterioration in the air quality, coupled with the increased proportion of PM2.5 pollutants in the ambient air, points towards the heavy and rapid contribution of secondary particulate formation as the key cause of the ongoing pollution spike in the NCR region. The light drizzle resulted in elevated relative humidity levels, which, along with calm wind speeds and high gaseous pollutant concentrations (SOX, NOX and other pollutants such as NH4) acted as a catalyst towards the rapid formation of secondary particulates, resulting in a mechanism where fine particulate matter concentrations continue to spike rapidly.
The formation of secondary particulates is usually associated with the meteorological conditions prevalent in Delhi during peak winter, in the months of December and January. The unusual occurrence of such a phenomenon at such scale during this time of the year indicates shift in weather patterns the influence of changing climatic conditions. The impact of ongoing Cyclone Maha, which is currently over the Arabian sea and is likely to make landfall this week, is also a factor that needs to be considered.
However, the occurrence of such secondary particulate formation definitely points at the elevated concentration of SOX, NOX and other such gaseous pollutants, which normally remain undiscussed during the conversation about air pollution in India. These gases are important elements which contribute to secondary particulate formation, and ultimately to higher PM levels. Therefore, in terms of addressing the sources of emissions, the control of gaseous pollutant emissions at their sources is necessary alongside particulate matter emission reduction.
What action is being taken?
The Environment Pollution (Prevention and Control) Authority for Delhi and NCR, or the EPCA, is a Supreme Court Appointed Committee that has been overseeing all air pollution related regulations in the NCR region since 1998. This committee has worked in coordination with the Central Pollution Control Board, as well as the State Pollution Control Boards of 5 states – Delhi, Haryana, Uttar Pradesh, Rajasthan and Punjab in the past. In 2016, the EPCA, along with the central as well as state governments began implementation of the Graded Response Action Plan.
In 2019 so far, the following measures have been announced under GRAP:
Country-wide efforts needed
In addition to the actions under GRAP, the various governments in the region have announced the following measures:
Given the situation in the region, various cities in the Delhi-NCR region on Sunday recorded AQI’s between 445 and 496, which is in the “Severe” category of Air Quality. SAFAR’s forecast for “the coming 2 days indicates that the “Air Quality is likely to remain in the “Severe” category” till November 5. However, there is a possibility of heavy rains, which will bring relief.
While Delhi receives the most media attention, many Indian cities are facing the same problems with air quality. These cities, often, also lack a capacity to take action on air pollution. Addressing air quality issues in the most impacted cities will require a country-wide effort. Collaboration and coordination across government levels is crucial. Implementation of judicial orders, and plans developed by empowered committees will also be key. In addition, industry and the public must also be engaged to create a holistic approach for air quality management.
Polash Mukerjee is Lead, Air Pollution and Climate Resilience at Natural Resources Defense Council.
First Published: IST