Air Pollution

Air pollution affects not only the quality of the air we breathe, but also the land and the water. What goes up must come down: just like anything else, pollutants released into the air will eventually make their way down to the earth's surface.

In particular, airborne nitrogen is a major contributor to pollution in the Chesapeake Bay and its rivers; it accounts for about one-third of the total load of nitrogen pollution to the Bay. Airborne chemical contaminants such as mercury can also affect the Bay.

What Types of Air Pollution Affect the Chesapeake Bay?

Nitrogen — a type of nutrient — and chemical contaminants are two pollutants that are emitted into the air and are of concern to the health of the Chesapeake Bay. These air pollutants can become water pollutants when they either fall onto the water itself or fall onto the land and are carried by stormwater runoff to the nearest waterway.

Nitrogen

Scientists estimate that approximately one-third of the nitrogen that reaches the Chesapeake Bay comes from air deposition.

Nitrogen oxides (NOx), ammonia and organic nitrogen are three specific nitrogen compounds that are released into the air and can harm the Bay.

• Nitrogen oxides (NOx) are primarily released into the air as a by-product of combustion (the burning of fossil fuels like oil, gas and coal). NOx accounts for approximately 60 percent of the inorganic airborne nitrogen that winds up in the Bay.
• Ammonia is primarily released into the air through evaporation and emissions from industry processes. Every living creature — including humans — releases wastes that include ammonia. The remaining 40 percent of inorganic airborne nitrogen that affects the Bay is from ammonia emissions.
• Organic nitrogen is released through organic nitrogen compounds (like pollen, nicotine and caffeine) that contain carbon.

Chemical Contaminants

Chemical contaminants that are released into the air and can affect the Bay include metals such as mercury and organic contaminants such as PCBs and PAHs.

• Mercury is released into the air when coal, oil, natural gas and hazardous wastes are burned.
• PCBs can pass into the atmosphere as a vapor from old electrical equipment.
• PAHs are released into the air when fuel is burned.

Where Does Air Pollution in the Chesapeake Bay Region Come From?

The Chesapeake Bay's NOx airshed — the land area where nitrogen emitted into the air can make its way to the Bay — is about 570,000 square miles, or nine times the size of the Bay's watershed. Nearly 50 percent of the airborne nitrogen that pollutes the Bay is from sources located in the Bay watershed. The other half comes from sources as far away as Ohio, Canada and South Carolina.

Within the airshed, there are four main sources of airborne pollutants: stationary and area sources, mobile sources, agricultural sources and natural 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 pollutants, such as power plants and chemical and manufacturing facilities.
• Area sources are smaller, clustered sources that collectively produce significant amounts of pollutants. These include dry cleaners and gas stations, which are located close to one another in cities, towns and suburbs.
• Mobile sources move. Cars, trucks and other on-road vehicles are part of this category. Non-road sources, such as boats, airplanes, gas-powered lawn tools and farm and construction equipment, are also mobile sources. Collectively, mobile sources are a significant contributor to air pollution.
• Agricultural sources are farm operations that can generate emissions of gases, particulate matter and chemical compounds. The main air pollutant from agricultural sources is ammonia, which emits from manure that is produced in animal houses, stored in holding areas and applied to the land as fertilizer.
• Natural sources are not caused by human activities. These include lightning, dust storms, forest fires, plants and trees, erupting volcanoes and wild animals in their natural habitat.

How Does Air Pollution Affect the Chesapeake Bay?

Pollutants released into the air are carried by winds and fall back to the earth's surface via rain, snow, fog or dry particles. Airborne pollutants that fall on the land can be transported by stormwater runoff or groundwater into the streams, creeks and rivers that eventually flow to the Bay.

In addition to its effects on the Bay itself, nitrogen released into the air can contribute to:

• Increased acidity of surface waters and soils. This can diminish the growth, reproduction and survival of trees and underwater life.
• The formation of ground-level ozone, which is known to cause serious human respiratory problems and damage plants and other animals.
• Contamination of drinking water sources as it filters through the ground and accumulates in groundwater aquifers.

Chemical contaminants released into the air can have the same effect as those released on the ground: they can persist in the environment and accumulate in the tissues of plants and animals, moving through the food web and affecting growth and reproduction in living creatures of all sizes.