NEW DELHI: High air pollution levels in Delhi have been generally associated with winters, when atmospheric inversion traps pollutants close to the ground and causes smog. It's time to revise that view. Of late, the air quality continues to be poor even when temperatures are high, indicating that bad air in the capital is not longer just a seasonal phenomenon accentuated by weather conditions.
In fact, in summer it's a double whammy, say experts. Not only do levels of fine, respirable particles (PM2.5) remain fairly high, there's a rise in toxic ozone (O3), making Delhi's summer air dangerous for health.
According to an analysis by the System of Air Quality Weather Forecasting and Research (Safar), between April 17 and April 20, the daily average PM2.5 levels went up from a 'good' 80 micrograms per cubic metre to 163, which falls in the poor category.
Ozone levels are also gradually rising as summer sets in, going up from 52 parts per billion (ppb) to 70 ppb during the same period. The safe standard for ozone is 50 ppb.
Delhi Pollution Control Committee's real time air quality at 6.30pm also showed PM2.5 and PM10 levels to be considerably high. The PM10 concentration at Punjabi Bagh was about three times the safe standard at 346 microgram per cubic metre and PM 2.5 was 106, when the safe standard is 60. At Anand Vihar, PM2.5 levels were 105 and PM10 556.
During winter, cold air with high concentration of pollutants is trapped close to the earth's surface because a layer of warm air acts as a lid on top of this layer. This effect is known as inversion. The summer heat ensures that inversion does not take place. Experts say particulate pollution, especially PM10, goes up in summer due to dust but this dust is coated with toxins due to polluted emissions from various sources.
Anumita Roychowdhury of Centre for Science and Environment (CSE)'s clean air programme said in summer it's a multi-pollutant crisis. "Ozone has severe health effects and can easily trigger respiratory distress among the vulnerable population. It is true that dust is a problem in summer but toxic pollutants from various sources cling to the dust particles. The dust acts as a carrier for other toxic substances."
Exposure to ozone can be dangerous even when these are slightly above the safe standard. Ozone tends to trigger immediate health impacts in those with respiratory conditions. Ozone forms from chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Emissions from industries, vehicles, petrol vapours and chemical solvents are some of the major sources of NOx and VOCs.
"High ozone levels cause acute problems such as irritation in the throat, restlessness, complications among asthmatics and others. The impacts of particulate pollution are chronic," said Dr S K Chhabra, head of cardiorespiratory physiology at Vallabhbhai Patel Chest Institute.
In winter, the number of hospitalizations and complications associated with air pollution go up substantially due to a number of reasons. The recovery time is longer in winter, and compounding infections are also higher when temperatures are low. Influenza viruses such as H1N1 are much more active in winter.
"Air pollution in winter and summer are different in nature. While in winter it's more from combustion, in summer it's often from natural sources such as dust," said Chhabra. While there are no scientific studies to confirm that number of people with respiratory illnesses is going up in Delhi, globally there is consensus that the incidence of respiratory conditions are rising.
