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CPCB, a look at the science behind the air quality index

Scattered across Delhi, like many antennae, are the monitoring stations – nine manual and three automatic. Three of these manual stations are run by the National Environmental Engineering Research Institute, financed by CPCB. These, along with Delhi Pollution Control Board, give the AQI.

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Aradhna Wal

Updated: Dec 30, 2015, 08:11 AM IST

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At 4 pm on Tuesday, as averages based of real time readings of New Delhi's air were rolled out in the laboratories of the Central Pollution Control Board, the city had a relatively better day. From the slew of 'Very Poor' days the capital saw this month, on Tuesday, at 269 air quality index (AQI), it was now only at 'Poor'. Instead of 'respiratory illnesses on prolonged exposure', Delhi's residents were only exposed to 'breathing discomfort to most people on prolonged exposure'.

These are the daily tabulations carried out by the scientists, statisticians and the technicians of the Air Laboratory of the CPCB, who have to monitor, and maintain, air quality across India. It is much in the spotlight as air pollution has become a health emergency, a talking point for media and the public, causing governments to respond with drastic measures. This conversation, say scientists, has become possible because of the AQI, a quantifiable way of explaining air quality to those who breathe, which was launched this year by the central government.

Scattered across Delhi, like many antennae, are the monitoring stations – nine manual and three automatic. Three of these manual stations are run by the National Environmental Engineering Research Institute, financed by CPCB. These, along with Delhi Pollution Control Board, give the AQI.

Out of the 12 established parameters to monitor pollution – Sulphur dioxide, nitrogen dioxide, PM2.5, PM10, Ozone, Lead, Carbon monoxide, ammonia, benzene, Benzo[o]Pyrene, Arsenic, Nickel – eight are monitored by the automatic stations at ITO, Dilshad Garden, Shadipur. These collect information and update it online in real time.

Scientist at the Air Laboratory for 29 years, DC Jakhwal, calls these stations the CPCB's white elephants. Necessary as they are, each costs 1.1 crore to set up, roughly 12 per cent of that to maintain the sensitive equipment annually -- eight machines for eight parameters – and depend heavily on connectivity to monitor remote areas. For now, the lab has 39 such stations across India connected to it, with Gaya joining on Tuesday itself.

"Over the years, because we have started to monitor better, and our knowledge has increased we've seen the PM2.5 and PM19 particulate matter increase in Delhi, with rapid urbanisation and increase in automobiles," Jakhwal told dna. Sulphur dioxide has gone down, as sulphur usage has decreased in diesel and gas. These two are consistently the most prominent pollutants in Delhi.

It is the manual processes that truly hit home how toxic Delhi air is. Unfolding the filter papers that have been processed as samples at the stations, Jakhwal showed how the pristine white paper had gone pitch black. These papers – three a day to monitor 24 hours, daily – are inserted in a dust sampler that sucks in air for them to collect the dust. These samples are later sent to CPCB, to detect metal. The gases are absorbed in a solution, TMC, that is analysed by a spectrophotometre. The average of these samples are released monthly, except on Diwali, day when CPCB works long hours while the country is on holiday.

This particular sample was from November 4, Nizamuddin, between 10pm to 6 am. Comparatively, the same day's samples from 7 am to 3 pm were a dull grey, indicating far less dust.

On top of the building, is the SODAR device – Sound waves and Radio Detection Range – that emits a sound wave to a maximum of a kilometre up in the air. The point where it comes back from, is the mixing height, where the maximum pollutants mix with the air, which informs scientists about conditions for dispersing.

"Engineers can establish these stations, technicians can run it, but you need people who understand atmospheric science, to understand the data," said Jakhwal. Hence, CPCB regularly absorbs students from various universities training them in their special sets of skills.

With two more automatic stations being set up, their biggest asset to maintain air quality, is knowledge, said Jakhwal, which has finally made people take note of the state of affairs.

Meanwhile, the honour of 'severe' air went to Muzaffarpur, Bihar, on Tuesday.

White elephants
Scientist at the Air Laboratory for 29 years, DC Jakhwal, calls these stations the CPCB's white elephants. Necessary as they are, each costs 1.1 crore to set up, roughly 12 per cent of that to maintain the sensitive equipment annually – eight machines for eight parameters – and depend heavily on connectivity to monitor remote areas. For now, the lab has 39 such stations across India connected to it, with Gaya joining on Tuesday itself.

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