HT launches pollution dashboard that puts air quality data in context

Delhi's official air quality figure was 350 on Tuesday, in the 'very poor' band and the city's worst since January 20. At 6pm, 11 of Delhi's 57 reporting stations were in the 'severe' band, with Jahangirpuri highest at 459 and Lodhi Road lowest at 212. The air at Safdarjung had been calm for most of Monday night, and Nasa's satellite had counted 167 farm fires in Punjab and Haryana that day, a count well short of the real number.

HT has brought all of these together on one screen in its new HT Pollution Dashboard. Available on the HT app and the website -- just type hindustantimes.com/breathe -- the new dashboard gives residents of Delhi and the National Capital Region (NCR) the government's own air quality figures, updated every hour, labelled with who measured it and when; juxtaposed with wind speed, wind direction, farm fires, and the mixing height above ground level where the toxins have settled.

Phone apps can show different numbers for the same hour, from different sensors and on different scales. HT uses only data from the Central Pollution Control Board (CPCB), the India Meteorological Department (IMD) and Nasa. The government goes by CPCB's figures when it halts construction or takes vehicles off the road, and HT's newsroom checks them.

On October 29, Delhi's official figure was 222, in CPCB's Poor band. Between that evening and the next morning, 60.5mm of rain fell at Safdarjung, 50mm of it in the three hours after 11.30pm. The next day's figure was 60, Satisfactory, a drop of 162 points and the sixth-biggest one-day fall in any October or November since 2015.

Two days later, on November 1, the figure was 261, Delhi's worst since April 17. The air at Safdarjung had been calm in six of the airfield's eight reports through the night, and Nasa's satellite had counted 106 farm fires in Punjab and Haryana on October 31. With the rain day in it, the week to November 1 was still the cleanest for those dates in 12 years.

Any one of those figures, taken alone, gives a misleading picture of the week, and it takes all of them together to see what happened. The argument over how far Delhi's monitors can be trusted will go on, but the way their numbers move, from hour to hour and against past seasons, remains the clearest guide to what is happening to the air the city breathes.

HT has reported on Delhi's air this way all season, setting the government's pollution figures beside the weather, the fires and the years before. The dashboard now does this for every reader, every hour, on one screen. Three agencies publish the figures it brings together, in a dozen places, and no other site sets them side by side.

At the top is CPCB's hourly average for Delhi, with how far it has moved since the same hour the day before. Beneath it is the official figure from CPCB's 4pm bulletin, which covers the 24 hours to 4pm. The two can be far apart in the morning: at 7am on November 1, the hourly figure was 207, while the last official figure, for October 31, was still 117.

Readers can tap "Use my location" to see the monitoring station nearest them, and the location stays on their phone. Delhi's stations are also ranked from worst to best, so readers can see how far their neighbourhood is from the city average.

Further down are the wind and rain at Safdarjung and a short reading, every morning and evening, of whether the weather helped clear the air or worked against it. On calm nights, smoke and dust stay close to the ground, and the morning figure tends to climb.

The farm-fire count is labelled an undercount every time it appears, because Nasa's satellite passes over Punjab and Haryana at about 1.30pm and most burning now happens later in the day. Readers can also compare this year's daily figures with every season since 2015-16.

The dashboard covers Delhi, Noida, Ghaziabad, Gurugram, Faridabad and Greater Noida, at hindustantimes.com/breathe and on the HT app.