It's probably the best time to be outdoors in the city. After inhaling highly-polluted air for months, Delhiites seem to be breathing easy with PM 2.5 (fine, respirable particles) levels remaining within the safe limits. The sudden spell of showers on Sunday and Monday washed out the suspended particles from the air, a rare phenomenon in Delhi.

The rain, however, has no impact on other polluting gases such as sulphur dioxide (SO2), oxides of nitrogen and others. "For the first time in the past five months, all particulate matter levels have come down to the green category. There will be good air quality on Tuesday and Wednesday too, according to our forecast model. Even ozone levels are low due to the overcast sky as production of ozone is dependent on sunlight," said Gufran Beig, project director, System of Air Quality Weather Forecasting and Research (SAFAR).

The pollution had been at the "severe" level—four to five times higher than the standard—in recent months. An analysis of Delhi's real-time air quality data by the Centre for Science and Environment showed that 65% of days in December had recorded "severe" or "hazardous" level of pollution. Last year, a report by the World Health Organization found Delhi to have the most polluted air among 1,600 cities.

According to Delhi Pollution Control Committee's real-time air quality monitoring levels at Punjabi Bagh, PM 2.5 levels ranged from 17 microgram per cubic metre to 25 microgram per cubic metre from 10.30am to 3.30am on Monday but levels rose again during peak traffic hours after 5pm when levels rose to 135 microgram per cubic metre.

At Mandir Marg too, PM 2.5 levels ranged from 25 to 60 microgram per cubic metre between 10.30am and 6.30pm. Delhi's 24-hour average PM 2.5 level on Monday was about 45 microgram per cubic metre, according to monitoring by SAFAR under the ministry of earth sciences.

Higher PM 2.5 levels are linked to several respiratory and cardiac conditions, including acute bronchitis, asthma complications, chronic obstructive pulmonary disease (COPD) and others. It can also cause arrhythmias and ischaemic heart disease. Arrhythmia is a disorder characterized by irregular heart beat or abnormal heart rhythm while ischaemic heart disease is associated with reduced blood supply to the heart.

Source: 3 March, 2015, The Times of India