Faulty samplers and data fudging hamper India's air pollution fight

India is changing the way it maps pollution, with an update to its air quality index. In its initial phase, eight pollutants will be tracked in 46 cities with populations exceeding a million people. After five years, the rest of the country will slowly be brought into the system.

At the launch, the minister for environment and forests, Prakash Javadekar, said it wouldn't be "business as usual'' anymore. The move couldn't have come a moment sooner.

Five months ago, the World Health Organisation declared Delhi to be the worst polluted city on earth. In a study spanning 1,600 cities across 91 countries, the organisation used India's own officially released data to show the city had the world's highest annual average concentration of microscopic airborne particles known as PM2.5.

These extremely fine particles of less than 2.5 micrometres in diametre are linked with increased rates of chronic bronchitis, lung cancer and heart disease as they penetrate deep into the lungs and pass into the bloodstream. Delhi's annual PM2.5 reading was 153 compared to London's 16. Indian officials contested the study's finding but agreed Delhi was as bad as Beijing, although the latter's PM2.5 reading was only 56.

In fact, Delhi's air quality may be even worse. The Economic Times reports that the central pollution control board compared some India-made PM2.5 samplers with international ones a couple of years ago.

A manufacturer of samplers, Rakesh Agarwal of Envirotech, candidly said: "There was a 100 per cent difference in readings.''