Glossary

This Clean Air Action Plan website reports on many parameters. This glossary tells you what all those parameters mean, and will help you understand the data better.

AQI Definitions
The AQI is divided into six categories and each category is assigned a color to help visualize the information on the Current AQI map.

 

 Good (0 to 50). Air quality is considered satisfactory, and air pollution poses little or no risk.

 

 Moderate (51 to 100). Air quality is acceptable; however, unusually sensitive people should consider limiting prolonged outdoor exertion.

 

 Unhealthy for Sensitive Groups (101 to 150). The following groups should limit prolonged or heavy outdoor exertion: People with heart disease, pregnant women, children and older adults, people with lung disease, such as asthma

 

 Unhealthy (151 to 200). Everyone may begin to experience some adverse health effects (e.g. difficulty breathing and throat irritation), and members of the sensitive groups may experience more serious effects. The following groups should avoid prolonged time outdoors: People with heart disease, pregnant women, children and older adults, people with lung disease, such as asthma.

 

 Very Unhealthy (201 to 300). This would generate a health alert suggesting that everyone may experience more serious health effects. The following groups should avoid all outdoor physical activity: People with heart disease, pregnant women, children and older adults, people with lung disease, such as asthma. Everyone else should avoid prolonged or heavy outdoor activity.

 

 "Hazardous" (greater than 300). This would trigger a health warnings of emergency conditions. The entire population is more likely to be affected. Everyone should avoid all physical activity outdoors.

Carbon Monoxide (CO)
Carbon Monoxide (CO)

Source: burning of gasoline, natural gas, coal, oil etc.

Health Effects: reduces ability of blood to bring oxygen to body cells and tissues; cells and tissues need oxygen to work. Carbon monoxide may be particularly hazardous to people who have heart or circulatory (blood vessel) problems and people who have damaged lungs or breathing passages.

Monitoring: The instrument measures the reduction in infrared light due to absorption of the light by CO.

Nitrogen Dioxide (NO2)
Nitrogen Dioxide (NO2)

Source: burning of gasoline, natural gas, coal, oil etc.

Health Effects: lung damage, illnesses of breathing passages and lungs (respiratory system).

Environmental Effects: nitrogen dioxide is an ingredient of acid rain (acid aerosols), which can damage trees and lakes. Acid aerosols can reduce ambient visibility. NO2 can also combine with volatile organic compounds in the presence of sunlight to form ground-level ozone.

Monitoring: O3 is injected into the instrument. The light given off by the chemical reaction between O3 and NO is measured.

Ozone (O3) ground-level
Ozone (O3) ground-level

Source: chemical reaction of pollutants; VOCs and NOx.

Health Effects: breathing problems, reduced lung function, asthma, irritates eyes, stuffy nose, reduced resistance to colds and other infections, may speed up aging of lung tissue.

Environmental Effects: ozone can damage plants and trees; smog can cause reduced ambient visibility.

Monitoring: The instrument measures reduction of UV light due to absorption of O3.

PAHs (polycyclic aromatic hydrocarbons)
PAHs (polycyclic aromatic hydrocarbons)

Source: PAHs are generally products of incomplete combustion – inefficient combustion of solid and liquid fuels such as coal, wood, kerosene, and jet fuel can lead to PAH formation. PAHs are often adsorbed on soot and other particulate matter emitted from combustion processes, and gasoline and diesel engines.

Health Effects: The toxicity of individual PAHs ranges from nontoxic to extremely toxic. EPA has classified seven PAH compounds as probable human carcinogens.

Monitoring: PAHs are measured using UV light to measure changes in the particle electrical charge. The real-time instrument measures total PAHs in the air sample, and does not distinguish between the individual PAHs. Additional 24-hour integrated filter samples are collected every third day at the POLA monitoring stations and analyzed in a laboratory. This monitoring system will distinguish 32 individual PAHs collected on the filters, including the seven probable carcinogens. Another analysis program will compare the results of these two measurement programs.

Fine Particulate Matter (PM2.5); (e.g., soot, smoke)
Fine Particulate Matter (PM2.5); (e.g., soot, smoke)

Source: Primarily formed by burning of wood, diesel and other fuels; and by industrial plants.

Health Effects: nose and throat irritation, cardiovascular and respiratory problems.

Environmental Effects: fine particulates are the major cause of reduced visibility (haze) in parts of the United States. In addition, particles can acidify lakes and streams; damage sensitive forests and farm crops; and stain and damage stone and other materials.

Monitoring: The particulates are filtered through an inlet that only allows particulates smaller than 2.5 micrometers to enter. These particulates are then collected on a tape for a specified duration and compared to a baseline tape using Beta radiation.

Coarse Particulate Matter (PM10); (dust, smoke)
Coarse Particulate Matter (PM10); (dust, smoke)

Source: agriculture (plowing, burning off fields); paved and unpaved roads, wind erosion.

Health Effects: nose and throat irritation, cardiovascular and respiratory problems.

Environmental Effects: Particles can acidify lakes and streams; damage sensitive forests and farm crops; and stain and damage stone and other materials.

Monitoring: The particulates are filtered through an inlet that only allows particulates smaller than 10 micrometers to enter. These particulates are then collected on a tape for a specified duration and compared to a baseline tape using Beta radiation.

Sulfur Dioxide (SO2)
Sulfur Dioxide (SO2)

Source: burning of coal and oil, especially high-sulfur coal from the Eastern United States; industrial processes (paper, metals), diesel fuel.

Health Effects: breathing problems, may cause permanent damage to lungs.

Environmental Effects: SO2 is an ingredient in acid rain (acid aerosols), which can damage trees and lakes. Acid aerosols can also reduce ambient visibility.

Monitoring: The instrument measures SO2 fluorescence when exposed to UV light.

Ultrafine Particles (UFP)
Ultrafine Particles (UFP)

Source: UFPs are produced by combustion processes. In an urban environment, gasoline and diesel engines are the major source of these particles, and the highest UFP number counts tend to be found near freeways. High UFP counts are very localized and dependent on nearby source activity, and they exhibit large geographical and temporal variation.

Health Effects: UFPs have much higher numbers and surface areas compared to larger particles, and these particles can be inhaled and deposited deeper into the lungs. This may allow UFPs to transport more toxic pollutants into the lungs than larger particles. However, at this stage, the information on health effects of UFPs is limited.

Monitoring: UFPs are measured using a particle counter. The instrument used to monitor for UFPs can count particles in the size range of 6 to 2,500 nanometers (0.006 to 2.5 µm), although most particles will be in the UFP size range below 100 nm. The instrument reports data in particle counts per unit volume, or particles/cm3.

Data Averaging Periods
Data Averaging Periods

1-hour averages – These averages are the mean of samples collected within a one-hour period.

8-hour samples (for CO) – This average is the mean of samples collected within the most recent eight hours.

8-hour samples (for O3) – This average is the highest 8-hour average measured within a calendar day.

24-hour samples – This average is the mean of samples collected within the most recent 24 hours.