CHENNAI: With the World Health Organisation raising the bar in setting revised air pollution reduction targets, the new cut-off limits for particulate matter, ozone and sulphur dioxide could make for a stiffer challenge in cities like Chennai.

WHO recently unveiled its new Air Quality Guidelines with dramatically lower standards for levels of pollutants in the hope that stricter air pollution standards could reduce deaths in polluted cities by 15 per cent.

Reducing particulate matter, identified as a major concern, can produce the biggest health benefits. Produced mainly by the burning of fossil fuels, particulate matter has been increasingly linked to respiratory illness and heart disease.

Most cities currently have levels of particulate matter - known as PM10 - in excess of 70 micrograms per cubic meter. The new guidelines recommend cutting levels of PM10 to 20 micrograms, a reduction WHO says can reduce deaths from air pollution by 15 per cent a year.

The recommended daily limit for ozone is down from 120 to 100 micrograms per cubic meter — a stiff challenge for cities where sunny days are the norm when ozone concentrations are highest, causing respiratory problems and asthma attacks. The guidelines call for reducing levels of sulphur dioxide from 125 to 20 micrograms per cubic meter.

"These guidelines represent the most consensual and contemporary assessment of health effects of air pollution," said Kalpana Balakrishnan, professor and head, Department of Environmental Health Engineering, Sri Ramachandra Medical College and Research Institute (Deemed University), who was in the team that finalised the document.

The Tamil Nadu Pollution Control Board will need to have a closer look at the new cut-offs before chalking out a compliance strategy, a spokesperson said.

The Air Quality Guidelines, put together after a worldwide consultation with more than 80 leading scientists and review of recent studies from all regions of the world, for the first time addresses all regions of the world and provides uniform targets for air quality. These targets are far tougher than the national standards currently applied in many parts of the world — and would, in some cities mean, reducing current pollution levels by more than three-fold.

The revised guidelines have emerged from a backdrop of increasing evidence of the adverse health effects of air pollution in the form of particulate matter or sulphur dioxide, ozone or nitrogen dioxide.

According to WHO, air pollution is estimated to cause approximately 2 million premature deaths worldwide per year with developing countries accounting for more than half this burden.

While the WHO accepts the need for governments to set national standards according to their own particular circumstances, these guidelines indicate levels of pollution at which the risk to health is minimal. In that sense, the new guidelines provide the basis for all countries to build their own air quality standards and policies supporting health with solid, scientific evidence, said Dr. Balakrishnan.

The guideline level for nitrogen dioxide remains unchanged; however, meeting these limits, which are essential to prevent the health consequences of exposure such as bronchitis, remains a great challenge in many areas where car traffic is intensive. The guidelines also propose progressive interim targets and provide milestones in achieving better air quality.