A Look at Visible and Invisible Air Pollution

Eilene Toppin Ording

Driving past a factory with a white plume floating out of the smokestack, the average person may think they’re seeing a big pollution problem. Maybe they are, but maybe not.

Water Vapor is Everywhere

Most white plumes, especially those seen in cold weather, contain simple water vapor. Feedwater tanks for boilers always have a stack that emits plain water vapor and air. Water is one of the main byproducts of combustion, so water vapor is found in coal-fired, natural gas and oil-fired boiler stacks.

Cooling towers also have plumes that are mostly water, though a small amount of chemicals used to treat the water may be present. A cooling tower without water treatment chemicals will grow algae or other biological species. Metal corrodes faster with pure water in contact with it, so some anti-corrosion treatment is usually needed. Some chemicals chosen for cooling towers in the past have since been banned for their toxicity to the environment.

Industrial facilities run with heated and cooled processes as a matter of course. Food companies for instance bake, fry, or boil then cool, even freeze finished product. These facilities and others will emit a great deal of water vapor with the discharge of hot gases from the process.

Combustion Products that Nobody Wants

The number one pollutant that most people are currently concerned about is carbon dioxide. No matter what is burned, combustion produces end products. Hydrogen combustion produces water vapor. All combustion of carbon based fuels must produce carbon dioxide. Carbon dioxide is colorless and odorless and not detectable from the street side of the fence.

Particulates and Acid Gases

Particles of dust or chemicals are of more concern to persons suffering from asthma and lung diseases. These are called particulates in the environmental community. Particulates are grouped by size: larger than 10 microns, less than 10 microns, and less than 5 microns.

Black smoke contains visible particulates that a filter can catch. White smoke can contain the smaller size particulates. Companies use fabric filters and other more elaborate methods to catch the particulates before they leave the stack.

Acid gases contain the precursors of acids. When combined with precipitation, they form acid rain. The two types most commonly regulated are sulphur dioxides and nitrogen oxides, sometimes called SO2 and NOX. Forests are damaged by acid rain. Major legislation regulates the output of acid gases from power plants and large boilers. Neither SO2 nor NOX are visible to the naked eye.

Volatile Organic Chemicals

Some of the truly toxic chemicals fall into the category that chemists call “organic.” That refers to the carbon-hydrogen atom structure of these chemicals. Gasoline is a mixture of organic chemicals. Volatile chemicals evaporate easily, even without heating.

Products of combustion contain organic chemicals and some of them are rather nasty to the human body. The gases emitted from a car’s tailpipe, even after the catalytic converter, are a laundry list of carcinogens. The rate of emission of the toxic chemicals depends on the efficiency of the engine or external combustion source, such as a boiler. Almost all are invisible, though they do sometimes have an odor.

Visible Safety

Uncontrolled pollution is not always visible, but sometimes the controlled gas stream is visible. Water is commonly used to strip particulates or acid gases out of the air, causing the white plume. A flare or visible flame on a stack usually indicates that volatile organic chemicals are being burned instead of being released untreated. The burning increases the carbon dioxide released, but the toxics are reduced to relatively harmless gases.

Citizens who wish to be proactive about industrial pollution can report black smoke. Something is probably wrong with a stack where nothing was visible yesterday, but today is belching visible emissions. Be aware that rules allow for malfunctions to occur for up to six hours, depending on the age of the facility and local environmental law.

A better approach to finding out what the factory next door is emitting is to go to the Environmental Protection Agency website and look for community resources. Citizens can search databases by zip code to find out what toxic chemicals and pollutants may be emitted by the company down the road.

Smokestack, darnok on morgueFile.com
Think that toxic chemicals are spewing into the air from every factory chimney? What is visible is not usually the most harmful.

Driving past a factory with a white plume floating out of the smokestack, the average person may think they’re seeing a big pollution problem. Maybe they are, but maybe not.

Water Vapor is Everywhere

Most white plumes, especially those seen in cold weather, contain simple water vapor. Feedwater tanks for boilers always have a stack that emits plain water vapor and air. Water is one of the main byproducts of combustion, so water vapor is found in coal-fired, natural gas and oil-fired boiler stacks.

Cooling towers also have plumes that are mostly water, though a small amount of chemicals used to treat the water may be present. A cooling tower without water treatment chemicals will grow algae or other biological species. Metal corrodes faster with pure water in contact with it, so some anti-corrosion treatment is usually needed. Some chemicals chosen for cooling towers in the past have since been banned for their toxicity to the environment.

Industrial facilities run with heated and cooled processes as a matter of course. Food companies for instance bake, fry, or boil then cool, even freeze finished product. These facilities and others will emit a great deal of water vapor with the discharge of hot gases from the process.

Combustion Products that Nobody Wants

The number one pollutant that most people are currently concerned about is carbon dioxide. No matter what is burned, combustion produces end products. Hydrogen combustion produces water vapor. All combustion of carbon based fuels must produce carbon dioxide. Carbon dioxide is colorless and odorless and not detectable from the street side of the fence.