NOx refers to a group of toxic gases that are also called nitrogen oxides (e.g. Nitrogen oxide NO and Nitrogen dioxide NO2). These gases have been listed among the six criteria pollutants by the US EPA, and are closely monitored and regulated under a cap-and-trade program. NOx gases are emitted from various sources, esp from anthropogenic activities such as th euse of fossil fuels in internal combustion engines (including cars, trucks, motorcycles, rickshaws etc), industrial/commercial/residential uses, and power utilities, esp coal and gas-fired plants.
According to the EPA, NOx causes several harmful effects, including:
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.
Climate Change – One member of the NOx, nitrous oxide or N2O, 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.
I just came across this chart showing NO2 levels in some major Pakistani cities (Reference). The levels are alarmingly high! Just for reference, the US National Ambient Air Quality Standards set the annual arithmetic average value of NO2 that is tolerable at 100 ug/m3. Even our cleanest cities are above that level.
Soon I will try to post something a bit more detailed on the deteriorating environmental air quality in major Pakistani cities, the major sources of air pollution, and some ideas that are being mulled around in the environmental policy circles. I will attempt to apply a technology/science lens to the available information to look at both the complexity of the problems, and validity of the proposed solutions.