Photochemical Smog The brownish shroud

We can survive without food for several days, without water for a few days, but we cannot survive more than a few minutes without air. Yet we are altering the chemical make-up of air via rampant emissions of gaseous and particulate matters. The pollutants vented into the atmosphere come from a number of different sources natural and man-made. Among the man-made sources, most harmful are the effluents from vehicles and emissions from industries. They are precursors to the formation of smog, a term coined to describe a mixture of smoke and fog.
Smog is produced through a complex set of photochemical reactions involving particulate matter (dust, soot, etc) and various gases nitrogen oxides, water vapor, carbon monoxide, and carbon dioxide which come out through the exhaust system of a vehicle. They react in the presence of sunlight to produce a witch's brew of virulent pollutants. Among some of the worse are formaldehyde, peroxyacyl nitrate (PAN), and acrolein. Furthermore, ozone is formed at the ground-level through chemical reactions involving unburned hydrocarbons in gasoline, volatile organic compounds, various oxides of nitrogen, and sunlight. The net result is a brownish orange shroud of air pollution called photochemical smog. In addition, smog in industrial towns forms when smoke and sulfur emissions from burning fossil fuels combine with fog. Smog occurs more frequently in communities situated in valleys with surrounding hills and mountains where there is less air circulation and more accumulation of pollutants in the air.
Ozone is one of the most prevalent chemicals in smog. Problematic ozone levels occur mostly on hot summer afternoons when there is little wind and temperatures soar above 30 degrees Centigrade. Effects of ozone are primarily health related. Lungs are ozone's primary target. It aggravates respiratory diseases, particularly asthma, emphysema, and chronic bronchitis. When inhaled, ozone can inflame pulmonary membranes causing significant temporary reduction in lung capacity, from 15 to 20 percent. Adults with respiratory diseases are most susceptible to the adverse effects of ozone. Even healthy adults engaged in strenuous outdoor activities like jogging, gardening, manual labor, etc., will suffer from ozone-related health effects. Ozone can also impair our immune system.
In tandem with ozone, the inherent toxicity in smog can cause chest pains, coughing, throat irritation, and shortness of breath. In the worst case scenario, it may contribute to lung cancer. Formaldehyde, a component of smog, is a colorless gas with pungent smell. It is toxic and will cause burning sensations in the eyes, nose, and throat. The PANs are extremely potent oxidant. They are irritating and harmful. They act like tear gas and irritate the skin, eyes, and nasal passages. The other component of smog, acrolein, is a colorless liquid with an acrid smell. It is a strong irritant for the eyes. Unfortunately, human body has very little defense against these pernicious effects of smog.
Children with asthma are especially vulnerable to the harmful effects of ozone and smog alike. Because of their physiology, they are much more likely than adults to develop smog-related lung damage. Even healthy children are at risk because their respiratory systems are still in the developmental stage.
To make a bad situation worse, smog remains under siege for days if it is accompanied by temperature inversion (TDS, 8 January 2013). We witnessed it earlier this month when major parts of China were trapped in a toxic blanket of smog leaving the citizens literally breathless. Scenes of Chinese cities smothered by smog are a disturbing reminder of the Great London Smog of 1952 which killed over 4,000 people. Ironically, smog-related problems are non-local. The pollutants in smog drift in the wind and can travel to faraway places making the smog in those places more severe.
For many years we viewed pollution as a sign of progress. Today, pollution is seen as signs of failed technologies. The “airpocalypse” in China is clear evidence our atmosphere is too finite to absorb the pollutants dumped into it. Also, it is disquieting to note that except for our lungs, we have run out of place to put them away. If we want to pursue a reasonably healthful existence, we have to live by the maxim “solution to pollution is dilution.” The air we breathe should not make us cough.
Next time you see the setting Sun painting the sky pink and orange, remember it is smog which made the colors so brilliant. There is an ugly story “behind every pretty picture.”