On Tuesday, the Indian government announced a big change in how the people of Delhi get their air quality data.

So far, the three agencies monitoring air quality in the city – the Central Pollution Control Board, the Indian Meteorological Department and the Delhi Pollution Control Committee – collect and disseminate their numbers separately. The Indian Meteorological Department  has digital displays across the city. The Central Pollution Control Board and the Delhi Pollution Control Committee put their numbers online.

But in the new system, the Delhi Pollution Control Committee and the Indian Meteorological Department  will stop making their numbers public. Instead, their data will be sent to the Central Pollution Control Board for analysis. "Authenticated air quality information will be communicated to Delhi Pollution Control Committee on daily basis for further dissemination to the public at large," the government statement said.

Coming at the end of a year where Delhi came to be known as one of the most polluted cities in the world, the announcement has been greeted with suspicion. The head of a company which manufactures air quality measuring instruments, who spoke to Scroll on the condition of anonymity, expressed concern that the government would start manipulating numbers in the guise of vetting them.

The fear is not far-fetched. Last year, when reporting about the flawed processes India uses to measure her air quality, this correspondant and his team were told by a senior official of the Delhi government that when the city's monitoring system was being set up, officials debated on whether to cap emission numbers being put out. “But luckily, the member secretary insisted we report the correct data,” he said.

As the article reported, there is pressure on the government to read down air quality numbers. Every time air quality worsens, there is a public outcry, followed by parliamentary questions. In recent times, the Delhi government has also been pulled up by the National Green Tribunal.

But Shashi Shekhar, the chairman of Central Pollution Control Board, maintained the recent changes are needed to fix the problems in the reporting of air quality data. Between the three agencies, Delhi has 21 monitoring stations, the highest number for any city in the country. But Shekhar said they were still inadequate for giving a representative view of the city. “We need to divide Delhi into representative zones and then move around some of the stations to get a better sense of the city's air quality,” he said. The need to relocate stations might be valid but questions remain.

How is a single, centralised system better than three independent agencies reporting air quality data?
Three independent agencies collecting (and reporting) air quality data introduces checks and balances. This was very evident during last Diwali. That night, at around 10 pm, "real-time" air quality data on the website of the Central Pollution Control Board was anything but real time. Its station at Civil Lines in north Delhi, for instance, reported air quality numbers captured on September 12, 2013.

In contrast, the Delhi Pollution Control Committee's numbers, getting updated every 30 seconds, painted a worrying picture. At 10.15 pm, at Delhi University near Civil Lines, the main indicators of air pollution, the particulate matter counts, PM10 and PM 2.5 stood at 1,000 and 995.60 respectively, vastly exceeding the safety limits of 100 and 60.

In the new system, these numbers won't be visible to the public, until the Central Pollution Control Board has audited them.

Shashi Shekhar, the chairman of Central Pollution Control Board, argues that there is a need for his organisation to audit the data. In the absence of a representative, city-wide overview, he says, the media is reporting the highest readings – from say, a busy intersection like Delhi's ITO traffic intersection – creating a possibly exaggerated picture of air quality in the city. This problem, he added, is intensified if the press uncritically reports outliers – numbers that might be too high or too low, possibly due to a technical glitch.

Wouldn't it be better to eliminate glitches than pore over data to spot and remove outliers? Glitches are a sign of poorly calibrated monitoring machines. Miscalibration is one way of manipulating high-end, realtime monitoring machines. Tell the machine that a 0.01% concentration of sulphur dioxide is actually a 0.001% concentration and all subsequent readings will be proportionately under-reported. If Central Pollution Control Board wanted to spot and remove outliers in Delhi Pollution Control Committee numbers, said one of its official, speaking on the condition of anonymity, it would be better to "regularly test the units' calibration [to make sure they are working well] instead of asking them to send their raw numbers over”.

Is the government planning to do away entirely with real-time numbers?
According to Shekhar, the new system will report real-time numbers after vetting. The Central Pollution Control Board would put out a 24 hour rolling average, an analysis of the last 24 hours, and a forecast. However, a second press release from the government, released a day after the first one, said the new system will report air quality concentrations only as averages. Concentrations of carbon monoxide will be reported as hourly and eight-hourly averages. That of PM 2.5 and PM 10 would be reported as a daily average.

There are two issues here. One, the distinction between reporting real-time numbers and as averages is critical. Shekhar said peaks and troughs can create a misleading image of air quality. “I need to give 24-hour averages so that people have the correct sense of air quality,” he said. The member secretary of Central Pollution Control Board, AB Akolkar agreed. “A 24-hour average is the global standard for reporting PM 2.5,” he said.

But the CEO of a company which manufactures air quality measuring instruments countered the view. “Only reporting averages hides peaks and troughs and artifically reduces air pollution numbers,” he said.

An official working with the Central Pollution Control Board added, “If I have a kid suffering from asthma and I want to decide whether he should play in the evening or not, what good is a 24-hour average?”

Why is the government focusing on Delhi?
India's capital, despite all the glitches mentioned by Shekhar, has the country's best air quality monitoring system. It has 21 realtime monitoring stations. In contrast, the Central Pollution Control Board website shows Mumbai, Patna, Kanpur and Ahmedabad have just one station each.

This, incidentally, is the main reason why Delhi has India's most polluted air. It has the best air quality monitoring system of all cities. In contrast, others State Pollution Control Boards – out of apathy or wilful negligence – do not report numbers correctly. An excellent instance of this is Bihar. Last year, while working on the air quality stories, we found that its station in Patna was reporting – for months together – an Ozone level of - 46.

Given the endemic mess in India's air quality monitoring systems, the key question is: why is the government focusing on Delhi instead of getting the rest of the country up to the level where Delhi is?