Clearing the air

  • Blog Post Date 23 February, 2017
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In this article, Naini Jayaseelan, former Secretary, Environment, Government of National Capital Territory of Delhi, discusses the pitfalls of basing policies to curb air pollution on comparisons of air quality indices across countries or cities.

Just when Delhi had recovered from two phases of the odd-even experiment1 in January and April 2016, and the dust was settling at least until the following winter when another phase was expected, it was definitely a calmer time to reflect on the real issues.

However, in November 2016, due to a sudden but anticipated hike in the pollution levels, which was the worst in the last 20 years, the Supreme Court solicited and heard the responses of the Central Pollution Control Board (CPCB), Ministry of Environment and Forests (MoEF), and the state governments of the National Capital Region, and directed framing and submission of a Graded Response Action Plan (GRAP) for various categories of the national Air Quality Index (AQI). The GRAP lists suggested actions for each category – ‘moderate to poor’, ‘very poor’, ‘severe’, and ‘emergency’. The GRAP has now been notified by the MoEF and an institutional arrangement for its implementation has been put in place.

It is an accepted fact that Delhi has the dubious distinction of being classified as one of the most polluted cities in the world, based on the results of various studies undertaken at various points of time. These studies make headlines for a few days and it is but natural that the general public, fed on these media reports, demands that the concerned agencies wake up and take concrete and visible action against air pollution. But beyond the eye-catching media reports, it is important to pause and reflect whether the comparisons made between countries and across cities are even valid and relevant. Do these voluminous reports give a clear picture, to any decision-maker or to the common man, of the air quality? For the sake of the confused public, the air needs to be cleared on whether before deciding and implementing policy prescriptions, are we even aware of the dangers inherent in inferring policy prescriptions on the basis of these studies? Are we even asking the right questions so that the well-intentioned answers we want to hear and propagate as public policy prescriptions are actually the right answers to the right questions?

Defining the air quality index: Lack of consistency

Air pollution is a complex and dynamic phenomenon, caused by a combination of different pollutants. The main pollutants identified are particulate matter (PM10 and ultrafine PM2.5), nitrogen dioxide or nitrous oxide (NOx2), sulphur dioxide or sulphur oxide (SOx), carbon monoxide (CO), ozone, benzene, etc. The World Health Organization (WHO) has formulated guidelines on four parameters - PM10 and PM2.5, O3, NOx, and SOx. WHO has also laid down their average acceptable limits over a 24-hour period. WHO air quality guidelines are based on extensive scientific evidence on the health effects of air pollution. However, these guidelines are not legally binding on countries and can at best be looked upon as a moral guiding force for countries to set their own national standards. In fact, most countries have set their own standards for different parameters.

Some countries have an AQI that captures the extent of air pollution in a single figure, rather than the values of individual pollutants. The recently developed AQI for India includes eight parameters with different weightage, which includes lead, benzene, SOx, NOx, CO, ozone, and ammonia, in addition to PM10 and PM2.5. The USEPA (United States Environmental Protection Agency) AQI, however, focusses only on four major air pollutants regulated by the US Clean Air Act: ground-level ozone, PM, CO, and SOx. In such a scenario, can comparisons of AQI be valid?

Firstly, if we look at individual pollutants, PM consists of a mixture of both solid and liquid droplets and there is enough evidence that fine particles (those with less than 5 mm diameter) can cause or aggravate a large number of health problems, especially for those with existing diseases or for the aged and children. Based on the effects on health indicators, Indian guidelines exist for both short-term (24 hours) and long-term (annual) limits for both PM10 and PM2.5. It is an accepted fact that PM levels in most Indian cities are about 4-5 times higher than in American and European cities. PM is one of the major concerns of air pollution in Indian cities in general and in Delhi in particular. But basing decisions on studies on PM only would never give the right policy prescriptions. Alternatively, a study on benzene only or ozone only, may not be enough to categorise a city as being polluted. For example, studies exclusively on levels of NOx or SOx, both of which are toxic and formed as a result of combustion processes, can give vastly different results from studies on PM. High SOx and NOx levels would require stringent action on thermal power plants in the vicinity rather than control of tail pipe vehicular emissions. Hence, the appropriate policy prescription varies.

Complexities of monitoring air quality

Monitoring of air pollution is both difficult and complex. The methodologies differ not only across countries but also between the central and state government agencies in India. Manual and automatic monitoring stations are bound to give vastly different results, even in the same location.

Leave aside different methodologies, the same method of monitoring will give different readings if the monitoring instruments are differently calibrated. A robust system of checking calibrations of monitoring instruments is still not in place. Very often, even if protocols exist, they are not followed.

The location of monitoring stations and instruments can give vastly different results even in the same city. Monitoring in a residential area or at a traffic intersection in the same city can throw up hugely different results. Hence, monitoring results from a pollution hotspot cannot, by itself, be generalised for the entire city or country.

Lastly, different meteorological conditions can give vastly different results. Adverse meteorological conditions can sometimes play a pivotal role in increasing the frequency of extreme pollution events. And there is no doubt that due to climate change, the frequency and duration of such events has increased in recent times. Comparisons of data during periods of sudden forest fires in Australia and Indonesia with Indian or Chinese data can lead to completely inaccurate results and meaningless conclusions. In fact, the winter pollution in Delhi is a result of – among other things - adverse metrological conditions like low wind velocity, low mixing height, etc.

Recall that different agencies produced vastly differing results during the odd-even experiments. This then becomes an ideal recipe to confuse the public and add further haze.

Concluding thoughts

The utility of AQI lies in helping residents to protect their health by alerting them to plan their outdoor activities accordingly. However, a single AQI figure, cannot capture differences in the levels of air pollution across cities, leave alone countries. Comparisons based on the AQI method are actually misleading because every country has its own parameters and its own scale. The levels of air pollution at which other countries evoke their action plans are actually far lower relative to India. The GRAP will be more effective if it takes into account the factors enumerated above, in defining and measuring air quality.

Let us then not get drowned in the cacophony of comparisons. Distilling the data is the key for policy prescriptions. The public waiting for solutions needs more understanding than mere rhetoric and hopefully this would lead to more informed policy decisions.

May be we could learn a thing or two from cities like London or Paris, which before pressing the panic button ensure that public transport is not only available but accessible. In Paris, by law, all companies employing more than nine employees actually pay for the running of the efficient metro system. A systemic change in both the existing laws as well more efficient monitoring of air pollution levels can only then clear the air.


  1. In an attempt to address Delhi’s grave pollution problem, the state government experimented with a driving restrictions policy for a fortnight in January and then in April 2016. The Delhi odd-even policy prohibited cars with license plates ending with an odd digit from being on the road on even days of the month, and vice versa. The government issued several exemptions from the policy, notably for women drivers, vehicles running on compressed natural gas (CNG), and two-wheelers. The policy was in effect every day for 15 days each in January and April except Sundays, and from 8 am to 8 pm.
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