the exercise of developing methodologies for building two basic tools of air quality management for Delhi - an air quality index (
aqi) and an emission inventory - was launched at an international workshop in the capital recently. The workshop was organised by the Delhi-based Centre for Science and Environment (
cse), and was attended by experts from the
us , Sweden, India, Pakistan, Bangladesh and Nepal.The Indian participants included representatives from the Central Pollution Control Board (
cpcb), Delhi Pollution Control Committee (
dpcc), National Environmental Engineering Research Institute (
neeri), Indian Institute of Petroleum (
iip), Automotive Research Association of India (
arai), Delhi College of Engineering (
dce) and the Indian Institute of Technology (
iit), Delhi. In 1997,
cse had published a study which showed that Delhi's air pollution claimed one life every hour. But, despite the warning and worsening pollution levels, no action has yet been taken by the government to inform the public of the daily pollution levels and how it affects people's health. The government maintains a silence, while semi-government and independent research organisations make sporadic half-hearted efforts, which only add to the confusion. This is primarily because there are numerous gaps in our knowledge about the sources of the deadly cocktail of pollutants and the quantities emitted in the air everyday. In view of its extended campaign for 'Right to Clean Air',
cse decided to take the initiative to assess the ambient air quality through an
aqi and the emission levels through an emission inventory. An
aqi is used to keep the public informed about the pollution level and its effect on the health of different groups of people like asthmatics, children and the elderly. The result was three days of hard deliberations. And this was only the beginning.
The challenges Developing an
aqi for Delhi had its peculiar problems. Models employed by other countries were not found suitable here.
The first step in developing an
aqi is to identify the major pollutants and decide how to convey to the public the effects of current levels of the pollutants on health. The general practice the world over is to bring out a daily
aqi report on the pollutant which records the highest ambient concentration. But Delhi has the distinction of having a number of pollutants exceeding the permissible limits on any given day. The other issue, therefore, was to be able to provide warnings of the health effects of high levels of a mixture of pollutants simultaneously exceeding their safe limits.
The first task was to identify the pollutants which should be taken into account while preparing Delhi's air quality index? Experts made it clear that the three pollutants - sulphur dioxide, nitrogen dioxide and suspended particulate matter - regularly monitored at all sites by the
cpcb, were not enough. For a proper
aqi, it is absolutely essential that the range of pollutants monitored be increased to include pollutants like carbon monoxide, ozone and
pm10 and that the daily levels of all pollutants be disclosed to the public. According to Joseph Cassmassi, senior meteorologist in the South Coast Air Quality Management District, California, the highest priority should be given to
pm2.5 (particulate matter smaller than 2.5 microns),
pm10 (particulate matter smaller than 10 microns), carbon monoxide and ozone.
According to the experts, measurement of total suspended particulate matter would serve no practical purpose. Even monitoring
pm10 is not enough, they felt. The focus of monitoring particulate matter should shift to
pm2.5
because these are fine particles emitted by combustion sources and can penetrate deeper into the lungs, causing more harm than
pm10, they pointed out.
Credibility of data The experts who analysed the air quality data and geographical and meteorological features of Delhi, were puzzled to find that data provided by
cpcb shows extremely low levels of ozone in the city. However, when Viney P Aneja, Research Professor at the North Carolina State University, used the air pollution data of Delhi in an air quality model, he found that the ozone level could be as high as 4,000 microgrammes per cubic metre (g/cum) an exceedingly high figure. He also pointed out that ozone has a strong correlation with particulate matter and the very high concentration of particulate matter suggests that the ozone concentration could be high as well. Commenting on why
cpcb data failed to record such high ozone levels, he said that it could be due to the faulty location of ozone monitors.
This brought into focus another critical issue the number of air quality monitors that are needed to adequately capture the amount of air pollution before the air quality data is used to calculate the
aqi. At present there are only 12 monitoring sites in Delhi, but going by the
us epa standards, the
aqi need to be notified for every 350,000 people. In other words, Delhi would need at least 30 monitoring stations and need to notify
aqi for all these sub-areas. More importantly, for the data to be credible, all the monitors would have to be online, to provide air pollution data by the minute.
Another question hotly debated was whether to include toxic air pollutants like benzene in the
aqi. It is now a well-known fact that there is an extremely high concentration of benzene, a known carcinogen, in Delhi's air. However, the experts suggested that a cancer risk map of Delhi should be prepared based on the annual average concentration of benzene, rather than announcing its daily levels, as according to the World Health Organisation, there is no safe level for benzene.
AQI: what and how much A crucial question to emerge was that since the content of the
aqi notification would be vital to the success of the system, what message would it convey to the public and how was the air quality to be categorised so as to reflect the health effects of air pollution in the simplest terms. The experts explained that since protection of public health is the main aim of developing an
aqi, it should be able to clearly spell out which group of the population is at risk and to identify the responsible pollutant. Arden Pope, Professor at Brigham Young University pointed out that it is not sufficient to tell people whether the quality of air they are breathing is good or bad. According to him, a majority of the people affected by pollution do not understand its health implication. Therefore, it should be the primary aim of the
aqi to inform them about the consequences.
The experts found that if the
aqi of the
us , which has six air quality descriptor categories explaining the corresponding health effects, is applied to the pollution levels of Delhi, most of the days will fall under the category of unhealthy air quality, if not worse. Thus, they felt it is more important to capture the health effects at various levels of pollution exceeding the permissible limit rather than focussing on the levels below the limit. Therefore, they recommended that the
aqi for Delhi should have five health-based descriptor categories, of which two should be below and three above the permissible limits.
Besides serving the purpose of an health advisory, the
aqi could also serve as a tool for two other major purposes, the experts pointed out. First, to educate people and galvanise them into action. Experiences in Western countries have shown that once people are made aware of the severity of the problem, they take the initiative by putting pressure on politicians and administrators to bring down the emissions and to make policy level changes. Second, it can be used as a yardstick to declare a pollution emergency to combat air pollution episodes when they occur due to very high emission rates and adverse meteorological conditions.
Experts like Kirk Smith, Professor of Environmental Health Sciences at the University of California, Berkeley, and Shankar Prasad, Community Health Advisor to the Chairperson of the California Air Resources Board, who argued strongly in favour of having pollution emergency measures, pointed out that these measures should be at two levels - voluntary and mandatory. However, the levels of
aqi at which a pollution emergency should be declared and the measures that should be taken to bring down pollution levels in the short-term were left to be discussed and developed.
But is an
aqi enough to capture the risk air pollution poses to the health of people? Some of the experts thought otherwise. Therefore, in addition to the
aqi they came up with another kind of index which can capture the long-term health effects of both criteria and toxic air pollutants. To deal with these chronic effects, they suggested the creation of a Chronic Pollutants Index (see box:
Is the AQI
enough?).
Emission Inventory But it is not enough to know only about the daily or monthly levels of pollution. For any air pollution control policy to be effective it is essential to know the source of the pollutants. This needs a detailed listing of the various sources of air pollution and the emission from them in a given time frame, for instance, a month or a year. This is what an emission inventory does. It is relatively easy to identify the sources of pollutants, but the crucial part is to quantify the pollution being emitted by a source. Only then can an action plan to control the emission of that pollutant be formulated.
Till date there have been a few attempts by agencies to find out the percentage contribution of various sources to the total air pollution load. But when the
cse surveyed these reports and presented the findings to the workshop, it became clear that these reports could at best be called indicative. For example, according to the
cpcb, more than 76 per cent of the carbon monoxide in the city's air comes from vehicular sources. However, in a startling revelation, Viney Aneja pointed out that a very large amount of carbon monoxide enters Delhi's air from adjoining areas. This brings to light the fact that no study has been conducted on pollutants which might enter Delhi's air basin from surrounding areas. Moreover, it was also pointed out by the experts that fine particles are not only emitted by combustion sources, but are also formed in the air by conversion of gases directly emitted by various sources. Sulphur dioxide and oxides of nitrogen, for instance, are known to form fine particles in the air in the form of sulphates and nitrates. Only a competent air quality model based on a detailed inventory can tell us about such atmospheric conversions.
Thus, it was clear that the whole exercise needs to begin from scratch. But what does that mean in Delhi's context? According to Linda Murchison, chief of the emission inventory branch, California Air Resources Board, preparing an emission inventory is a gradual process. It involves identification of the sources of pollution and the pollutants, their distribution and trend in emission and then to identify and track if existing control policies are effective in controlling pollution.
Making an emission inventory There are well-established methods across the world to prepare an inventory. The
us, which initiated the air quality monitoring and inventorying exercise in the 1970s, has developed a system of tracking the changes in the rate of emissions from different sources through photochemical modeling of air quality and trends. But that is not possible in the Indian scenario without first putting a basic source apportionment exercise in place, pointed out Eric Fujita, professor at the
us -based Desert Research Institute. Ake Iverfeldt of the Swedish Environmental Research Institute informed that the European Union has developed a method using satellite imagery to identify land use sectors. This information along with other data can be used to estimate emissions within a geographic area. This method has been used extensively in Europe.
However, preparing such an inventory for Delhi will be highly resource intensive. Therefore, the experts group felt the best way would be to have both long-term and short-term approaches. While the short-term exercise will involve developing a preliminary inventory in one to two years time by way of rapid survey and using existing emission factors for calculating emissions, the long-term exercise is extremely detailed and can take five to 10 years. Yet even the preliminary inventorying exercise will require measurements of actual emissions to fill up the gaps in our present knowledge.
In the absence of credible emissions data for Delhi, it is not possible to use sophisticated models currently being used in the
us and Europe. Therefore, a comprehensive pollution inventory exercise for Delhi has to begin with the conventional bottom-up approach, that is survey and actual measurement of emissions from different types of sources of pollution. Without actually doing emission measurement from various sources, it is not possible to find out how much different sources contribute to the total pollution load. However, to help prioritise this exercise, satellite-based emission estimates could be of great help, the experts pointed out. Such an exercise, which is a short-term activity, has the potential of pointing out the rate of emissions from different sources.
