Chennaiites are breathing toxic air for at least 100 days in a year, although it may not always be visible except when it shows up as smog. The concentration of harmful particulate matter (PM) in the city is several times higher than the prescribed limit.

An analysis of the Central Pollution Control Board (CPCB) data of the last four years establishes that levels of PM 2.5 - the most harmful pollutant - has shot up to as high as 995 ug/m3 on many occasions. The World Health Organisation prescribes 25 ug/m3 as safe limit, while India has fixed a standard of 60 ug/m3.

PM 2.5 particles are 20 times smaller than the width of human hair. On breathing this air, these ultra-fine particles are quickly absorbed into one's bloodstream, penetrating deep into the respiratory and circulatory systems. This sooty, smoke-filled air fills our lungs, affecting our ability to breathe properly and reducing our life expectancy. Even short-term exposures to these particles on high-pollution days can trigger symptoms of asthma and cause respiratory or cardiovascular health problems.