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How does air pollution become water pollution?

Air pollution doesn’t just cloud the air we breathe. It also harms our land and water.

What goes up must come down: just like anything else, pollution released into the air will eventually fall back to the earth’s surface. This process is called atmospheric deposition.

• Pollution is emitted into the air. Wind and weather can carry pollution over long distances.
• Eventually, air pollution falls on the land or water when it rains or snows, as well as through dry particles.
• Pollution that falls directly onto the water’s surface becomes water pollution. Air pollution that falls on the land can also become water pollution when it runs off into storm drains or soaks into groundwater.

What are the main sources of air pollution in the Chesapeake Bay region?

There are four main sources of air pollution in the Chesapeake Bay region: stationary and area sources, mobile sources, agricultural sources, and natural sources.

Stationary and area sources

Stationary and area sources do not move. They have a fixed location.

• Stationary sources are usually large point sources that release relatively consistent amounts of air pollution. Stationary sources include power plants, chemical facilities and manufacturing facilities.
• Area sources are smaller stationary sources such as dry cleaners and gas stations. Area sources are often clustered near each other, and can emit substantial amounts of pollution.

Mobile sources

Mobile sources move. Collectively, mobile sources produce a significant amount of air pollution.

Mobile sources include cars ans trucks, boats, airplanes, gas-powered lawn tools, farm and construction equipment, and other off-road vehicles.

Agricultural sources

Agricultural sources include farm operations that generate emissions of gases, particulates and chemicals.

Ammonia is the main type of air pollution emitted from agricultural sources. Ammonia comes from animal manure that is stored in holding areas and applied to the land as fertilizer.

Natural sources

Natural sources of air pollution are not caused by human activities. Natural sources include lightning, dust storms, forest fires, erupting volcanoes, and wild animals in their natural habitat.

What types of air pollution affect the Chesapeake Bay’s health?

Nitrogen and chemical contaminants are two kinds of air pollution that can eventually reach the Bay and its rivers.

Nitrogen

Airborne nitrogen is one of the largest sources of pollution to the Chesapeake Bay and its rivers. Scientists estimate that about one-third of the nitrogen that pollutes the Bay comes from the air.

Nitrogen oxides and ammonia are the two major types of airborne nitrogen that pollute the Bay.

• Anything that uses gas, coal or oil – including cars, trucks, boats and power plants – releases nitrogen oxides (NOx) into the air. NOx accounts for approximately two-thirds of the airborne nitrogen that winds up in the Bay. It is also a major contributor to ground-level ozone pollution.
• Ammonia emissions come primarily from animal operations on farms. Ammonia makes up the remaining one-third of nitrogen pollution that comes from the air.

About 50 percent of the airborne nitrogen that reaches the Bay comes from sources within the Bay watershed. The other half originates as far away as Ohio, Canada and South Carolina. The area of land where nitrogen released into the air can eventually wind up in the Bay is known as the Chesapeake Bay airshed. The Bay’s NOx airshed is very large: approximately 570,000 square miles, or nine times as large as its watershed.

When too much nitrogen gets in the water, large algae blooms can form. Algae blooms block sunlight from reaching bay grasses and lead to low-oxygen areas where no life can exist.

Chemical Contaminants

Mercury, PCBs and PAHs are three chemical contaminants that are released into the air and can pollute the Bay.

• Mercury is released into the air when coal, oil, natural gas and hazardous are burned. Power plants are the largest source of mercury emissions to the air.
• PCBs can escape from old electrical equipment and pass into the atmosphere as a vapor.
• PAHs are emitted into the air when gas, coal and oil are burned.

Once in the water, these contaminants bind to sediment and move through the food web when larger animals eat small, bottom-dwelling organisms. Humans can be exposed to these toxic chemicals when they eat contaminated fish. Fish consumption advisories are widespread throughout the Chesapeake Bay region due to mercury and PCB pollution.

How can we reduce air pollution in the Chesapeake Bay region?

To restore the Chesapeake Bay, we must also clean up our air. Overall, emissions of harmful pollutants such as nitrogen and mercury are decreasing. However, more reductions are needed to meet new pollution limits for the Bay and its rivers.

New federal and state regulations, as well as better technology, are significantly reducing harmful emissions from vehicles and power plants. However, ammonia emissions have remained steady. As stronger laws take effect and on-the-ground restoration efforts continue, overall air pollution is expected to decline even further.

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From Around the Web

• "What Goes Up… Goes Into the Bay" - The Baltimore Chronicle (Mar. 2001)
• Air Pollution - Chesapeake Bay Foundation
• Air Pollution and Water Quality - U.S. Environmental Protection Agency
• Frequently Asked Questions about Atmospheric Deposition: A Handbook for Watershed Managers - U.S. Environmental Protection Agency