The introduction of chemicals, particulate matter, or biological materials into the atmosphere that cause harm or irritate living organism or damage the natural environment is known as air pollution. The major causes of air pollution can be in the form of solid particles, liquid droplets, or gas. Smog, which is a mixture of smoke and fog, is a type of air pollution. Smog can be seen as a brownish tint or haze in the sky in some areas. Major causes of air pollution in the modern era which result in smog are vehicle emissions, internal combustion emissions, and industrial fumes. The vehicle emissions and industrial fumes combine with other emission sources to create photochemical smog.

City Smog
Credit: praegerr via Flickr

Photochemical smog was first described in the 1950s as the product of a chemical reaction of sunlight striking nitrogen oxides and volatile organic compounds in the atmosphere. Major causes of air pollution resulting in the formation of photochemical smog include motor vehicle engines, industrial manufacturing, and coal powered plants which release volatile organic compounds such as gasoline, paints, solvents, pesticides, and biogenic sources. The product of these reactions is airborne particles (also known as particulate matter) and ground-level ozone. Although some smog is present in all modern cities, problems with smog are worse in cities with sunny, warm, dry climates which have a large number of motor vehicles and in areas where hills or mountains restrict air flow, allowing gases to build up to harmful levels.

Major causes of air pollution resulting in problems with smog in developing countries include land and forest fires. The farmers or plantation owners use fire to clear tracts of land for planting crops. Volcanic eruptions are a natural source of air pollution. Cities in the path of volcanic eruptions may be affected by problems with smog created by the emission of high levels of sulfur dixode, which creates volcanic smog (also called vog).Human health effects are the most serious of the problems with smog. Senior citizens, children, and people with emphysema, bronchitis, and asthma are the most severely impacted from ingesting smog. The smog can inflame airway passages, decrease the lungs’ working capacity, cause shortness of breath, pain when inhaling, coughing, and wheezing. Smog can also cause eye and nose irritation as it dries out the protective membranes of the nose and throat, which interferes with the body’s ability to fight infection. Statistics show that increased hospital admission and respiratory deaths correlate to periods of high ozone levels.

Reduction efforts currently employed to combat the problems with smog are control technologies, land use planning, and regulation. Industries may use particulate control devises including mechanical collectors, electrostatic precipitators, baghouses, and particulate scrubbers. The mechanical separation method removes particulates, which are one of the major causes of air pollution, from the air by using rotating air flow within a cylindrical container to create a cyclone. Larger particulates are too dense to follow the tight curve of the cyclone, strike the wall, and then fall to the bottom of the cylinder where they are removed. Electrostatic precipitators force an induced electrostatic charge which impedes the ability of gases, such as dust and smoke, from the air. Baghouses are designed to carry heavy dust loads, and are composed of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system. Particulate scrubbers function by bringing the polluted gas in contact with a scrubbing liquid to remove pollutants and is usually used to remove pollutants from a furnace flue. Land use planning and regulation are also employed to reduce the buildup of pollutants in area which are highly susceptible to smog formation.