In the first week of September, Delhi government released newspaper advertisements claiming pollution in the National Capital had dropped by 25%. The advertisements appeared just as Delhi approaches its peak pollution season with crop burning due to begin in the neighbouring states of Punjab and Haryana.

In the advertisements, chief minister Arvind Kejriwal claimed that levels of PM 2.5 – or particulate matter the size of 2.5 microns – had reduced to an average of 115 between 2016 and 2018 from an average of 154 between 2012 and 2014. This amounted to a reduction by 25%.

Particulate matter consists of tiny particles that can enter the bloodstream and lungs. The permissible limit of pollutants PM 2.5 is up to 40 cubic metres and 60 cubic metres for PM 10 or particulate matter the size of 10 microns.

The reasons for this reduction were attributed to measures taken by the Delhi government: providing round-the-clock electricity, imposing hefty fines on violation of construction norms, implementing a court-mandated Graded Response Action Plan, opening two expressways to ease vehicular congestion on Delhi’s periphery and closing two thermal power plants operating within the city limits.

Delhi government cited data compiled by the Central Pollution Control Board, a statutory organisation that functions under the environment ministry. But an analysis of the data by revealed a hazy picture of the actual levels of pollution in the National Capital.

Delhi government's advertisement in The Indian Express on September 7, 2019.

What the data shows

The Delhi government based its claim on an analysis published by Centre for Science and Environment on August 30. Kejriwal quoted from the non-profit’s findings when he addressed a press conference about pollution levels on September 6.

Researchers of CSE claimed they had analysed data from the Central Pollution Control Board that had been “submitted to Parliament”. They also stated that there were “data gaps” in the numbers analysed from 2010 to 2014 and “major gaps” in data from 2014 to 2015.

The data showed that PM 2.5 levels were recorded as 118 in 2016. This came down to 106 in 2017, but rose to 121 in 2018, a 14% increase, according to the organisation.

Despite that, there was a 25% decrease in the PM 2.5 level average from 2016 to 2018 compared to the average taken between 2012 and 2014, the Centre for Science and Environment claimed.

But’s analysis found that the government has submitted different sets of pollution data to the Lok Sabha and the Rajya Sabha.

In the Rajya Sabha on February 11, Minister of Health and Family Welfare Harsh Vardhan furnished data on the average PM 2.5 levels while answering a question on the “deteriorating air quality in Delhi”. Vardhan’s answer stated that the annual average for PM 2.5 levels was 135 in 2016, 124 in 2017 and 115 in 2018. He attributed the numbers to “available data”.

These numbers vary from the ones that appeared in the Lok Sabha a few months later. On July 12, while responding to a question in Lok Sabha on the “rising pollution levels in the country”, Minister of Environment, Forests and Climate Change Prakash Javadekar gave details of particulate matter levels according to the National Air Monitoring Program’s manual recordings.

The Central Pollution Control Board along with other State Pollution Control Boards monitors the air quality in 240 cities across the country under the National Air Monitoring Program.

Javadekar’s answer stated that annual averages of PM 2.5 levels in Delhi was 118 in 2016, 106 in 2017 and 121 in 2018. These figures were also cited by the Delhi government.

Three days later, however, different numbers appeared in an answer in the Rajya Sabha. On July 15, Minister of State for Environment, Forest and Climate Change Babul Supriyo, while answering a question on “pollution in Delhi”, claimed that there was a “reduction of 7.3% in PM 2.5 levels in 2018 over 2017 and 14.8% over 2016”. These percentage reductions were taken from the numbers cited by Vardhan in February.

Furthermore, data recorded by the Delhi Pollution Control Committee recorded numbers in stark contrast to the ones cited by the Central Pollution Control Board. The pollution committee monitors 26 air quality stations across Delhi. The Central Pollution Control Board, on the other hand, runs 12 stations and relies on eight other station operated by the Indian Meteorological Department. Both the Central Pollution Control Board and the Delhi Pollution Control Committee publish the pollution readings on their websites.

The annual averages calculated by the Delhi Pollution Control Committee that were accessed by state that the average PM 2.5 levels from 2016 to 2018 was 131, which is 15% lower than the annual average of 154 from 2012 to 2014 – not 25%, as the Delhi government has claimed.

“It can be debated how the claim of 25% was made,” said an official from the Delhi Pollution Control Committee requesting anonymity.

Data gaps?

Experts said there were several gaps in the available data to conclude that PM 2.5 levels had reduced by 25% in Delhi.

For instance, some monitors run by the Central Pollution Control Board did not record pollution levels daily, said Hem Dholakia of Council on Energy, Environment and Water. “We could not get daily averages for 2014 when the CPCB had seven stations,” he said. This, he said, made it difficult to calculate the yearly average. “We had to rely on the annual reports published by the CPCB for numbers we could not verify.”

Dholakia said that such gaps made it difficult to assess policy interventions. “Such gaps do not allow us to reach conclusions about whether such policies have worked or not.”

Other analysts said that they took the Central Pollution Control Board’s data with a “pinch of salt” because it manually monitored air quality, which means samples of data are collected once or twice a week and later analysed.

“We do not know what is missing [in data collected manually],” said Santosh Harish of Centre for Policy Research. Harish said that meteorological conditions also impacted the yearly averages of particulate matter. “This is what tends to complicate matters when it comes to drawing conclusions.”

Broadly, Harish said that PM 10 levels, of which PM 2.5 is a subset, have remained the same over the years. “The increases and decreases we see yearly in PM 10 levels can be attributed to weather changes,” he said.

Besides, experts also pointed that it was difficult to compare data from the last two years with data from 2013 to 2015. This is because the number of monitoring stations in Delhi have significantly increased from just four in 2010 to 46 at present.

“There are much lesser data gaps in 2018 than in previous years,” Harish said. “This would also make 2018 a good base year to start with.”