The Delhi government’s decision to launch a 15-day trial to limit cars on the roads based on their registration numbers has been greeted with a vociferous debate. Those supporting the move cite statistics that only one-tenth of Delhi uses cars to commute to work and yet this minority takes up the majority of the roads, leading to pollution and congestion. On the other side, those opposing the plan argue that such an odd-even formula has not worked perfectly anywhere in the world.
The cacophony has drowned out another, equally important, debate on Delhi’s noxious air: just how much of the capital’s pollution is caused by emissions from cars?
In July, facing a rap from the National Green Tribunal for its failure to check the capital’s worsening air, the central government had confessed that it doesn’t know what causes the pollution. Just a few months before that, it had filed an affidavit in the court claiming that vehicles are not a major factor behind the pollution and it wouldn’t help to ban old diesel vehicles.
Conflicting results
The Aam Aadmi Party government is restricting cars with odd and even numbered licence plates on alternate days in the hope of reducing the ultra-fine particulate matter or PM 2.5 emissions.
An Indian Institute of Technology-Kanpur report commissioned by the state two years ago had underlined the high levels of the particulate matter 2.5 which can travel deep into the respiratory system, causing ailments such as emphysema and cancer. At the same time, the report had noted that cars and jeeps contribute less than 10% of the ultra-fine pollutant – trucks, on the other hand, are bigger polluters, and a sizeable portion of PM 2.5 comes from road dust.
As per the report, while dust accounts for up to 35% of PM 2.5, domestic cooking, power plants and industrial emissions together contribute another 25% to 35%.
This was just one example of the lack of consensus on the culprits of Delhi’s pollution. Even if it’s clear that vehicles, industry, household smoke and agricultural fires contribute to the pollution levels, there’s less clarity on which component contributes how much.
A study from 2013 on the long-range transfer of airborne pollutants around Delhi said that particulate matter less than 10 micrometres in diameter, or PM 10, is being meteorologically carried to the capital from areas outside it. Another study by IIT-Delhi last year concluded that vehicles are the worst polluters of Delhi, followed by industries, power plants, and domestic sources.
Yet another study conducted by the Central Pollution Control Board in 2007-’10 concluded that while vehicular emissions are responsible for high nitrogen oxide levels, PM 2.5 is caused due to road dust. The Delhi-based Centre for Science and Environment, which monitors air pollution closely, had trashed the CPCB study, faulting its methodology.
“The CPCB study is the one most commonly used to refer to Delhi’s air pollution problem but it’s a little dated now and things have changed,” said Bhargav Krishna, research fellow at the Public Health Foundation of India. “But the study is now more than five years old. The entire character of Delhi has changed since its release. The vehicle population has nearly doubled in the city. So it is not necessarily representative of the current sources of air pollution in Delhi.”
Contested conclusions
Experts suggest that duplication of efforts in studying Delhi’s pollution doesn’t help. The central government and the city authorities constantly battle it out with their respective data and research, both of which apparently suffer from anomalies.
“There are many reasons why there’s no conclusive insight into causes of the Delhi pollution so far but duplication of monitoring is the biggest reason,” said Polash Mukherjee, a researcher working on air pollution with the Centre for Science and Environment. “Each government authority is working against each other with their respective departments and hence, there’s no consensus.”
Mukherjee cautioned against relying overly on any specific study, and added that policymakers should take methodology and limitations of each report into account before writing legislations. For instance, many studies use data collected in the past – that is, secondary data – and extrapolate conclusions from it, while others collect data during a specific time period and estimate indicators for the rest of the year, again ending up skewing the analysis.
“Some studies measure data only at certain time periods when the pollution from agricultural fires in neighbouring states is peaking,” Mukherjee said. “Those studies are prone to overestimating the impact of these fires while they miss out on what causes pollution during the rest of the year.”
A researcher who works on analysing pollution levels recorded by government meters said he has often found discrepancies in the data from CPCB and the Delhi Pollution Control Committee.
Both these organisations have roughly equal number of monitors in the city, he said, “but the pollution readings often vary more than they should. Sometimes, there is gross underreporting of pollution levels, which has the potential to spoil secondary research and impact long-term policies.”
Bhargav Krishna of the Public Health Foundation of India contends that uniformity and reliability is also affected because there are different monitors collecting different pollution data.
“Three agencies which collect data in the city have more than 20 stations in the city,” he said. “The data collection is not standardised. They are not necessarily measuring the same parameters. For instance, many of the CPCB and other monitors don’t measure PM 2.5 at all and even the measurement of PM 2.5 across different monitors is taken at different points of time. So you can't really do a retrospective analysis on these levels because they weren't measured at all."
In the past, CSE has slammed the government for underreporting pollution levels or not raising an alarm about the health hazards. As recently as two months ago, while the organisation found that the pollution levels on the night of Diwali were alarmingly high, the government data showed a slight dip in the pollution level as compared to the previous year.
The problem, CSE argued, was the fact that the government data didn’t take into account the real health impact of the ambient pollution levels. Even if road dust and vehicular pollution contribute less to the overall pollution levels, they hurt residents’ wellbeing much more because of the proximity.
“We may have power plants at a distance or an industrial zone which has other polluting sources, but vehicular pollution poisons the air we breathe every day and has to be a priority,” Anumita Roy Chowdhury of the Centre for Science and Environment had told Business Standard.
In the same vein, the Air Quality Index may not present the clearest picture of the pollution levels because it’s far from the actual sources of pollution.
“We go by the ambient air quality which is measured by monitors situated on high towers,” said Krishna. “That is not the true representation of your exposure to pollution since your source of pollution is the tail of the next car on the road. Hence, the quality of the air one is breathing is much worse than what the monitor will tell you, because it’s simply far from the source.”
Analysts say that there are other problems too with studies. Many of them estimate the number of vehicles because even the latest data is not real-time. Also, several studies use a common practice of estimating emissions from, say, one car to calculate roughly out how much all cars would emit.
“In places like Hong Kong, systems are much more efficient simply because there’s a clear hierarchy of organisations having a clear mandate,” said Mukherjee. “There’s no-one to interfere or misguide them and policies are made after careful deliberations. What we need is a central authority, working independently on collecting and analysing pollution data. This politics over policies needs to give way to science.”
We welcome your comments at
letters@scroll.in.
The cacophony has drowned out another, equally important, debate on Delhi’s noxious air: just how much of the capital’s pollution is caused by emissions from cars?
In July, facing a rap from the National Green Tribunal for its failure to check the capital’s worsening air, the central government had confessed that it doesn’t know what causes the pollution. Just a few months before that, it had filed an affidavit in the court claiming that vehicles are not a major factor behind the pollution and it wouldn’t help to ban old diesel vehicles.
Conflicting results
The Aam Aadmi Party government is restricting cars with odd and even numbered licence plates on alternate days in the hope of reducing the ultra-fine particulate matter or PM 2.5 emissions.
An Indian Institute of Technology-Kanpur report commissioned by the state two years ago had underlined the high levels of the particulate matter 2.5 which can travel deep into the respiratory system, causing ailments such as emphysema and cancer. At the same time, the report had noted that cars and jeeps contribute less than 10% of the ultra-fine pollutant – trucks, on the other hand, are bigger polluters, and a sizeable portion of PM 2.5 comes from road dust.
As per the report, while dust accounts for up to 35% of PM 2.5, domestic cooking, power plants and industrial emissions together contribute another 25% to 35%.
This was just one example of the lack of consensus on the culprits of Delhi’s pollution. Even if it’s clear that vehicles, industry, household smoke and agricultural fires contribute to the pollution levels, there’s less clarity on which component contributes how much.
A study from 2013 on the long-range transfer of airborne pollutants around Delhi said that particulate matter less than 10 micrometres in diameter, or PM 10, is being meteorologically carried to the capital from areas outside it. Another study by IIT-Delhi last year concluded that vehicles are the worst polluters of Delhi, followed by industries, power plants, and domestic sources.
Yet another study conducted by the Central Pollution Control Board in 2007-’10 concluded that while vehicular emissions are responsible for high nitrogen oxide levels, PM 2.5 is caused due to road dust. The Delhi-based Centre for Science and Environment, which monitors air pollution closely, had trashed the CPCB study, faulting its methodology.
“The CPCB study is the one most commonly used to refer to Delhi’s air pollution problem but it’s a little dated now and things have changed,” said Bhargav Krishna, research fellow at the Public Health Foundation of India. “But the study is now more than five years old. The entire character of Delhi has changed since its release. The vehicle population has nearly doubled in the city. So it is not necessarily representative of the current sources of air pollution in Delhi.”
Contested conclusions
Experts suggest that duplication of efforts in studying Delhi’s pollution doesn’t help. The central government and the city authorities constantly battle it out with their respective data and research, both of which apparently suffer from anomalies.
“There are many reasons why there’s no conclusive insight into causes of the Delhi pollution so far but duplication of monitoring is the biggest reason,” said Polash Mukherjee, a researcher working on air pollution with the Centre for Science and Environment. “Each government authority is working against each other with their respective departments and hence, there’s no consensus.”
Mukherjee cautioned against relying overly on any specific study, and added that policymakers should take methodology and limitations of each report into account before writing legislations. For instance, many studies use data collected in the past – that is, secondary data – and extrapolate conclusions from it, while others collect data during a specific time period and estimate indicators for the rest of the year, again ending up skewing the analysis.
“Some studies measure data only at certain time periods when the pollution from agricultural fires in neighbouring states is peaking,” Mukherjee said. “Those studies are prone to overestimating the impact of these fires while they miss out on what causes pollution during the rest of the year.”
A researcher who works on analysing pollution levels recorded by government meters said he has often found discrepancies in the data from CPCB and the Delhi Pollution Control Committee.
Both these organisations have roughly equal number of monitors in the city, he said, “but the pollution readings often vary more than they should. Sometimes, there is gross underreporting of pollution levels, which has the potential to spoil secondary research and impact long-term policies.”
Bhargav Krishna of the Public Health Foundation of India contends that uniformity and reliability is also affected because there are different monitors collecting different pollution data.
“Three agencies which collect data in the city have more than 20 stations in the city,” he said. “The data collection is not standardised. They are not necessarily measuring the same parameters. For instance, many of the CPCB and other monitors don’t measure PM 2.5 at all and even the measurement of PM 2.5 across different monitors is taken at different points of time. So you can't really do a retrospective analysis on these levels because they weren't measured at all."
In the past, CSE has slammed the government for underreporting pollution levels or not raising an alarm about the health hazards. As recently as two months ago, while the organisation found that the pollution levels on the night of Diwali were alarmingly high, the government data showed a slight dip in the pollution level as compared to the previous year.
The problem, CSE argued, was the fact that the government data didn’t take into account the real health impact of the ambient pollution levels. Even if road dust and vehicular pollution contribute less to the overall pollution levels, they hurt residents’ wellbeing much more because of the proximity.
“We may have power plants at a distance or an industrial zone which has other polluting sources, but vehicular pollution poisons the air we breathe every day and has to be a priority,” Anumita Roy Chowdhury of the Centre for Science and Environment had told Business Standard.
In the same vein, the Air Quality Index may not present the clearest picture of the pollution levels because it’s far from the actual sources of pollution.
“We go by the ambient air quality which is measured by monitors situated on high towers,” said Krishna. “That is not the true representation of your exposure to pollution since your source of pollution is the tail of the next car on the road. Hence, the quality of the air one is breathing is much worse than what the monitor will tell you, because it’s simply far from the source.”
Analysts say that there are other problems too with studies. Many of them estimate the number of vehicles because even the latest data is not real-time. Also, several studies use a common practice of estimating emissions from, say, one car to calculate roughly out how much all cars would emit.
“In places like Hong Kong, systems are much more efficient simply because there’s a clear hierarchy of organisations having a clear mandate,” said Mukherjee. “There’s no-one to interfere or misguide them and policies are made after careful deliberations. What we need is a central authority, working independently on collecting and analysing pollution data. This politics over policies needs to give way to science.”
