NOx

NOx: What is it?

Nitrogen oxides, or NOx, is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. Many of the nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide (NO2) along with particles in the air can often be seen as a reddish-brown layer over many urban areas.

Where does it come from?

Nitrogen oxides form when fuel is burned at high temperatures, as in a combustion process. The primary manmade sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. NOx can also be formed naturally.

Health and Environmental Impacts of NOx

NOx causes a wide variety of health and environmental impacts because of various compounds and derivatives in the family of nitrogen oxides, including nitrogen dioxide, nitric acid, nitrous oxide, nitrates, and nitric oxide.

Ground-level Ozone (Smog) — is formed when NOx and volatile organic compounds (VOCs) react in the presence of sunlight. Children, people with lung diseases such as asthma, and people who work or exercise outside are susceptible to adverse effects such as damage to lung tissue and reduction in lung function. Ozone can be transported by wind currents and cause health impacts far from original sources. Millions of Americans live in areas that do not meet the health standards for ozone. Other impacts from ozone include damaged vegetation and reduced crop yields

Acid Rain — NOx and sulfur dioxide react with other substances in the air to form acids which fall to earth as rain, fog, snow or dry particles. Some may be carried by wind for hundreds of miles. Acid rain damages; causes deterioration of cars, buildings and historical monuments; and causes lakes and streams to become acidic and unsuitable for many fish.

Particles — NOx reacts with ammonia, moisture, and other compounds to form nitric acid and related particles. Human health concerns include effects on breathing and the respiratory system, damage to lung tissue, and premature death. Small particles penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease such as emphysema and bronchitis, and aggravate existing heart disease.

Water Quality Deterioration — Increased nitrogen loading in water bodies, particularly coastal estuaries, upsets the chemical balance of nutrients used by aquatic plants and animals. Additional nitrogen accelerates «eutrophication,» which leads to oxygen depletion and reduces fish and shellfish populations. NOx emissions in the air are one of the largest sources of nitrogen pollution in the Chesapeake Bay.

Global Warming — One member of the NOx, nitrous oxide, is a greenhouse gas. It accumulates in the atmosphere with other greenhouse gasses causing a gradual rise in the earth’s temperature. This will lead to increased risks to human health, a rise in the sea level, and other adverse changes to plant and animal habitat.

Toxic Chemicals — In the air, NOx reacts readily with common organic chemicals and even ozone, to form a wide variety of toxic products, some of which may cause biological mutations. Examples of these chemicals include the nitrate radical, nitroarenes, and nitrosamines.

Visibility Impairment — Nitrate particles and nitrogen dioxide can block the transmission of light, reducing visibility in urban areas and on a regional scale in our national parks.

EPA’s Efforts to Reduce NOx

The U. S. Environmental Protection Agency (EPA), states, and local governments work as partners to reduce emissions of NOx. Reducing emissions of NOx is a crucial component of EPA’s strategy for cleaner air.

Emissions standards for motor vehicles

Since the 1970s, EPA has required motor vehicle manufacturers to reduce millions of tons of NOx from their products, resulting in significant improvements to public health. As a result of the Tier 2 program, all cars, SUVs, pickups, and vans will be 77-95 percent cleaner by 2009. The requirements are phased in, starting in 2004. The program will also result in cleaner-burning gasoline that contains 90 percent less sulfur. Through its clean diesel truck and buses program, EPA reduced the level of sulfur in highway diesel fuel by 97 percent starting in 2006, and will reduce NOx emissions by over 90%. The Clean Air Nonroad Diesel Rule will cut nonroad diesel vehicle exhaust emissions by more than 90 percent and fuel sulfur levels by 99 percent, beginning in 2007.

Emission standards for electric utilities

To help reduce acid rain, EPA devised a two-phased strategy to cut NOx emissions from coal-fired power plants. The first phase, finalized in a rulemaking in 1995, aimed to reduce NOx emissions by over 400,000 tons per year between 1996 and 1999. The second phase began in 2000, and aimed to reduce NOx emissions by over 2 million tons per year. The second phase reduction goal has been surpassed, in part due to additional state-initiated NOx reductions in the Northeast.