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What is Visible Air Pollution? | Visible Air Pollution | Photochemical Smog

The atmosphere is almost completely made up of invisible gaseous substances. Most major air pollutants are also invisible, although large amounts of them concentrated in areas such as cities can be seen as smog. One often visible air pollutant is particulate matter, especially when the surfaces of buildings and other structures have been exposed to it for long periods of time or when it is present in large amounts. Particulate matter is made up of tiny particles of solid matter and/or droplets of liquid.Natural sources include volcanic ash, pollen, and dust blown by the wind.

Coal and oil burned by power plants and industries and diesel fuel burned by many vehicles are the chief sources of man-made
particulate pollutants, but not all important sources are large scale. The use of wood in fireplaces and wood-burning stoves also produces significant amounts of particulate matter in localized areas, although the total amounts are much smaller than those from vehicles, power plants, and industries.

Smog hanging over cities is the most familiar and obvious form of air pollution. But there are different kinds of pollution—some visible, some invisible—that contribute to global warming. Generally any substance that people introduce into the atmosphere that has damaging effects on living things and the environment is considered air pollution.

Carbon dioxide, a greenhouse gas, is the main pollutant that is warming Earth. Though living things emit carbon dioxide when they breathe, carbon dioxide is widely considered to be a pollutant when associated with cars, planes, power plants, and other human activities that involve the burning of fossil fuels such as gasoline and natural gas. In the past 150 years, such activities have pumped enough carbon dioxide into the atmosphere to raise its levels higher than they have been for hundreds of thousands of years.

Other greenhouse gases include methane—which comes from such sources as swamps and gas emitted by livestock—and chlorofluorocarbons (CFCs), which were used in refrigerants and aerosol propellants until they were banned because of their deteriorating effect on Earth’s ozone layer.

Another pollutant associated with climate change is sulfur dioxide, a component of smog. Sulfur dioxide and closely related chemicals are known primarily as a cause of acid rain. But they also reflect light when released in the atmosphere, which keeps sunlight out and causes Earth to cool. Volcanic eruptions can spew massive amounts of sulfur dioxide into the atmosphere, sometimes causing cooling that lasts for years. In fact, volcanoes used to be the main source of atmospheric sulfur dioxide; today people are.

Smog alerts in large urban areas across the country are not uncommon these days, and exposure to particulate matter (PM) has long been known as a serious health threat, linked to respiratory problems, heart attacks, lung cancer and most recently potentially deadly blood clots. With so many sources of the combustion processes that produce these fine particles, it may come as no surprise that this type of pollutant is three times as dangerous to human health as previously thought.

Scientists with the Air Resources Board say up to 24,000 Californians die an average of 10 years prematurely each year from exposure to PM over a long period of time. Children, the elderly, and those with weakened immune systems are more at risk of experiencing the adverse effects of PM exposure, even in small increments. They also found that the shipping of goods throughout the state is accountable for approximately 3,700 deaths per year and emissions from the ports of Los Angeles and Long Beach account for around 120 deaths per year.

Their report, called “Methodology for Estimating Premature Deaths Associated with Long-term Exposures to Fine Airborne Particulate Matter in California,” was based on the analysis of 60 studies worldwide, including studies by the World Health Organization (WHO), and was presented May 22 to the California Air Resources Board. “Particle pollution is a silent killer,” said Mary Nichols, Air Resources Board Chairman. “We must work even harder to cut these life-shortening emissions by further addressing pollution sources head-on.”

PM particles are especially dangerous because they are so small; 20 times smaller than the width of a human hair. These minute particles are inhaled deep into the lungs and embedded in tissue or absorbed into the bloodstream. PM comes from many sources, including trucks, passenger cars, off-road equipment, electric power generation and industrial facilities, wood-burning fireplaces, as well as forest and agricultural burning.

Photochemical smog is also appearing in regions of the tropics and subtropics where savanna grasses are periodically burned. Smog’s unpleasant properties result from the irradiation by sunlight of hydrocarbons caused primarily by unburned gasoline emitted by automobiles and other combustion sources. The products of photochemical reactions includes organic particles, ozone, aldehydes, ketones, peroxyacetyl nitrate, organic acids, and other oxidants. Ozone is a gas created by nitrogen dioxide or nitric oxide when exposed to sunlight. Ozone causes eye irritation, impaired lung function, and damage to trees and crops. Another form of smog is called industrial smog.

This smog is created by burning coal and heavy oil that contain sulfur impurities in power plants, industrial plants, etc… The smog consists mostly of a mixture of sulfur dioxide and fog. Suspended droplets of sulfuric acid are formed from some of the sulfur dioxide, and a variety of suspended solid particles. This smog is common during the winter in cities such as London, Chicago, Pittsburgh. When these cities burned large amounts of coal and heavy oil without control of the output, large-scale problems were witnessed.

In 1952 London, England, 4,000 people died as a result of this form of fog. Today coal and heavy oil are burned only in large boilers and with reasonably good control or tall smokestacks so that industrial smog is less of a problem. However, some countries such as China, Poland, Czechoslovakia, and some other eastern European countries, still burn large quantities of coal without using adequate controls.

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