What is the thick haze that has enveloped Delhi and surrounding areas since Monday night?
It is smog. Smog occurs in a location that is far away from the actual source of pollution, and is a result of various factors: geography of the place, sunlight, calmness of winds, post-harvest crop burning, firing of brick kilns, pollution emitted by vehicles and industrial activity. The processes that lead to smog usually take place after the hazardous pollutants have drifted away in the wind. In Delhi, there are two winds — one carrying pollutants from stubble burning in Punjab and the other bringing in moisture from Uttar Pradesh — that are colliding above the national capital. This, combined with the near-still wind conditions near the ground level, have effectively trapped the pollutants, leading to the smog.
How is smog different from fog?
Fog in just condensed water vapour close to the ground. When water vapour saturates the air, the vapour starts to condense back into a liquid, as water droplets. These droplets, suspended in the air, appear as the thick haze that is known as fog. This results in low visibility. On the other hand, when pollution is high, nitrogen oxides and dust particles interact with sunlight to form ground-level ozone, leading to the building up of haze. This is smog, a result of a photochemical reaction of sunlight with pollutants that have been released into the atmosphere.
What are these pollutants?
WHO classifies particulate matter — the major components being “sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water” — into two broad types, PM10 and PM2.5, with the numbers indicating the diameter of the particles in microns. In Delhi, the ground-level ozone and PM 2.5 play the most significant role in formation of smog.
Chronic exposure to both PM10 and PM2.5 can lead to the “risk of developing cardiovascular and respiratory diseases, as well as of lung cancer”, says WHO. Both can penetrate and lodge deep inside the lungs; PM2.5 can “cross into the blood, causing damage in many organ systems,” says WHO.
How serious is this smog?
On Tuesday, Delhi’s air inched towards an “emergency scale”, with the Central Pollution Control Board recording the average air quality at 487 (it dropped to 448 on Wednesday) with an upper limit of 500. The Indian Medical Association, which has termed it a “medical emergency”, says that this air can be equated to smoking 50 cigarettes a day.
How harmful is it?
The direct impact of smog is on the lungs and the heart. Higher levels of nitrogen dioxide precipitate asthma; higher levels of sulphur dioxide precipitate chronic bronchitis.
Particulate matter, Delhi’s main concern, can damage the lungs and worsen asthma due to inflammation of the air tract. PM2.5, which can enter the lungs and also the lung lining, carries long-term risks including lung cancer, reduced lung function, skin diseases and reduction in life expectancy.
There has been evidence that PM2.5 can also enter the bloodstream, and prolonged exposure can cause cause inflammation of heart arteries. It can lead to thrombosis, when clotting inside a blood vessel obstructs the flow of blood, and can atherosclerosis, a condition in which the diameter of blood vessels is reduced and can result in hypertension. Recent studies have also linked high levels of particulate matter to strokes and nuero-degenerative illness.
Is everyone vulnerable?
The impact is gradual, when one has been exposed to pollutants for prolonged periods, and also depends on the age of the individual. The most vulnerable groups include newborns, children, pregnant woman and those with pre-existing health conditions such as asthma, chronic bronchitis, diabetes and cardiac diseases. There is evidence that high pollution can lead to premature birth, make pregnant women prone to miscarriage, and cause foetal growth problems and lethargy.
But when the levels are so high, they can also affect persons with no history of respiratory disease. The most common symptom is breathlessness, watering of the eyes and nose, burning sensation in the eyes, coughing, dizziness, headache and lethargy. Doctors in Delhi have been seeing patients with “smoker’s cough” in healthy patients with no history of respiratory illness.
What precautions can people take?
Children and elderly can wear air masks when outdoors. The efficacy of these, however, has not yet been proven, and it is safer for all, across age groups, to avoid walking when the smog is heavy. Doctors recommend that the vulnerable population take an influenza vaccination before the onset of the season, and that those suffering from chronic illnesses visit a physician.
How long will the smog remain?
Union Environment Minister Harsh Vardhan said Tuesday’s air pollution was “the result of adverse meteorological conditions”. What that means, a Delhi government official explained, is that “Delhi and its neighboring areas have nearly still wind near the ground, but two wind masses — one from Punjab that’s bringing pollutants from crop burning and the other from eastern UP, which is bringing moisture — are colliding in the upper atmosphere. This is leading to pollutants being trapped.”
The Met department estimates the situation would continue until at least Saturday, when some wind movement is expected on the ground. “The situation is likely to improve on Saturday, but even then it will not clear away in a day,” said an official.
“The situation will clear if there is rain or winds,” the Delhi government official said. “But this is not a situation that will improve unless crop burning is handled, due to Delhi’s unique weather conditions.”