Air Pollution

Air pollution not only affects the quality of the air we breathe; it also impacts 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 poor water quality in the Bay and its tributaries.

What types of air pollution impact water quality?

Nitrogen and chemical contaminants are two groups of pollutants that are of concern to water quality and are known to be emitted into the air.

Nitrogen compounds include nitrogen oxides (NOx), ammonia and organic nitrogen. Scientists estimate that one-quarter to one-third of the nitrogen that enters the Bay comes from air deposition: nitrogen released into the air that falls onto the land and runs off into the water, or falls onto the water itself.

• Nitrogen oxides (NOx) are primarily released into the air as a by-product of combustion: the burning of fossil fuels like oil, gas or coal.
• Ammonia is primarily released into the air by evaporation and emissions from industry processes. Every living creature—including humans—releases wastes that include ammonia.
• Organic nitrogen is released through organic nitrogen compounds (like pollen, nicotine and caffeine) that contain carbon.

Chemical contaminants include mercury and other metals, 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 primarily released into the air when fuel is burned.

Where does air pollution come from?

The Bay's NOx airshed—the area where emission sources contributing the most airborne nitrates to the Bay originate—is about 570,000 square miles, or seven times the size of the Bay's watershed. Close to 50 percent of the nitrate deposition to the Bay is from air emission sources located in Bay watershed states. The other half comes from sources located as far away as Ohio, Canada and South Carolina. The nitrogen emitted throughout the airshed eventually reaches the Bay watershed's rivers, forests and wetlands.

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 urban and suburban areas.
• 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 contribute significantly to air pollution.
• Agricultural sources are farm operations that can generate emissions of gases, particulate matter and chemical compounds. The main pollutant 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 impact water quality?

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 runoff or groundwater into streams and rivers, adding to excessive nutrient loads to the Bay.

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

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

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 up the food web and impacting growth and reproduction in living creatures of all sizes.