Atmosphere And Weather

How is Air Quality Measured

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As many parts of society begin to focus more on the notion of being “green” many individuals, organizations, and even large businesses are beginning to realize the importance of caring for and preserving this planet. Air quality is an important part of Earth's overall health as well as the health of all its inhabitants. Air quality depends on many things including types and amounts of pollutants in the air, wind speed, atmospheric stability, and landscape. The environmental Protection Agency (EPA) along with its corresponding state run agencies is responsible for monitoring air quality.

The Clean Air Act was passed in 1970 (along with amendments in subsequent years) and the EPA was given the task of coming up with standards for air quality and protecting public health as well as the environment. This is a tremendous responsibility. Bad air can be created in many ways and is often referred to as stagnant air. Science writer, Desonie, points out that stagnant air collects more pollutants because clean air is not coming in to replace it, thus the build up of pollutants.

She goes on to say that seasons like winter and summer can create more bad air days for specific reasons. Winter often brings with it a build up pollutants like wood smoke. Summer can produce an overabundance of photochemical smog which is a type of air pollution produced when sunlight acts upon motor vehicle exhaust gases to form harmful substances such as ozone (O3).

Winds are important to air quality because they either move polluted air away or bring in fresh air to replace it. Strong winds can equal a quick cleansing of the air while little or no winds may mean stagnant air.

Temperature inversion is another key factor in air quality levels. Inversion is when warm air traps cool air beneath it creating a situation where the cool air cannot rise. The area becomes a sort of closed environment and any pollutant entering gets trapped. New York and Los Angeles are two cities well known for experiencing high levels of temperature inversion.

The EPA and its corresponding state run agencies utilize two main methods for tracking major air pollutants such as ozone, particulates, sulfur oxides, nitrogen oxides, carbon monoxide, and lead: measurements and approximations.


Measurements are made at over 4,000 ground stations located around the country. Data is collected at these stations hourly and daily and annual reports on the findings are developed.

Satellites are also used to monitor air quality because they can detect pollutants in ways that ground stations cannot.


Most people living in the United States are well aware of the requirement to get emissions inspections on most operating motor vehicles. Emissions are approximated using estimates of factors like vehicle miles traveled and fuel used. Attention is also paid to amount of goods produced and materials used. 

The EPA also uses a rating scale called the Air Quality Index (AQI)to help cities and areas that are not in compliance make improvements to the factors that impact air quality. The AQI makes people aware of the quality of the air on any given day. It is divided up into six categories: Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, and Hazardous. Desonie states that the AQI “is normalized so that, for each pollutant, values below 100 are healthful and those above 100 or not”.

States that do not meet the standards set forth by the EPA can suffer consequences such as sanctions or loss of federal funds for interstate highways. Maintaining good air quality is not only important for those living today, but it is essential for the health of future generations as well as for the survival of this magnificent planet.


Desonie Ph.D., Dana. (2007). Atmosphere: Air Pollution and Its Effects. New York: Chelsea House.

Mogil, H. Michael. (2007). Extreme Weather. New York: Black Dog & Leventhal Publishers.

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