Wonder why people are choking on Delhi's air much before Diwali? The reason is the calm weather conditions prevailing over the city which has led to the build up of several air pollutants. Such conditions also prevent the dilution and dispersal of air pollutants.
The rapid build up of pollution since the month of October, after the monsoons ceased, is stunning. For instance, in Civil Lines area in north Delhi, the PM 2.5 (particulate matter or air pollutants containing particles with 2.5 micrometre diameter or less) levels in the first week of October exceeded the permissible limit by 1.3 times. By the last week, the levels exceeded the standard four times over.
This month, the 24-hourly levels exceeded the standard by close to six times. On November 3 afternoon, the PM 2.5 levels in Punjabi Bagh area in west Delhi was 458 microgramme per cubic metre (ug/m3); at Mandir Marg it was 273, which was much higher than the safe level (see graph). The PM 2.5 levels in other areas of the city were as follows: R K Puram: 247 ug/m3, IGI Airport: 408.40 ug/m3, far exceeding the safe limit of 60 ug/m3. The ozone levels simultaneously touched 208.85 ug/m3, higher than the safe level at 180 ug/m3 at Civil Lines.
The prevailing calm weather conditions are indicated by very low wind speeds, recorded in the range of 0.12 to 1 metre per second in different locations. Studies indicate that small particles aggravate respiratory and cardiac symptoms in the short term and can lead to lung cancer in the long term.
| PM2.5 levels in Civil Lines, Delhi (October 1 to November 3, 2012) The levels exceed safe levels six times |
| Note: the redline indicates 24-hourly average standard of 60 microgramme per cubic metre Source: Based on DPCC data |
| Visibility at Palam airport, Delhi 1/01/2012 to 01/02/2012 |
| Source: http://amssdelhi.gov.in/ |
Besides particulate matter and ozone levels, nitrogen dioxide (NO2) and carbon monoxide (CO) levels too are exceeding the standards. These pollutants (NO2 and CO), come predominantly from vehicles. NO2 is a trigger for serious respiratory condition and sudden death syndrome among infants. CO curbs blood’s oxygen carrying capacity.
| CO levels in Civil Lines (26-31 October, 2012): Levels exceeding the standard on several instances. Levels exceed as much as 3.5 higher than the standard |
| Benzene level in Civil Lines (27-31 October, 2012): Benzene does not have a short-term standard. An indicative comparison of 24-hourly levels with the annual average standard indicates the levels are several times higher |
The potential of lower vehicular emissions in Indian cities
Multi-pollutant emissions inventory for the National Capital Region of Delhi
Status of the vehicular pollution control programme in India
Level of air pollution in Delhi
Urban outdoor air pollution database