Oregon Air Pollution Index
The Department of Environmental Quality provides a daily index of air quality for certain locations in Oregon. A description of this index and details are described below. By clicking on each paragraph title, you can get a more detailed explanation of the topic.
What is the Air Pollution Index?
The index is based in air pollution standard levels as defined by the Environmental Protection Agency. While the index ranges from 0 to 500, only values below 100 are considered healthful. Nationally this standard is known as the Pollution Standards Index. In Oregon, DEQ computes the index exactly the same way as the national index but it is called the Air Pollution Index (API). Each of the pollutants monitored in an area is translated to an index value. The highest value is reported for each area along with the pollutant that caused it, the general location and an overall air quality rating.
The API is computed in Portland, Salem, Eugene, Medford and Bend, which were chosen based on population and the availability of air pollution monitoring data.
The API is computed for the selected areas automatically twice every day. The process starts by collecting the most recent air pollution monitoring data from several monitoring sites in or near the selected areas. This process starts at 10 a.m. and 4 p.m. local time. After the data is collected, the computation is completed and the results are relayed to various agencies using computer generated FAX. In addition, this web site is updated. The process is normally done within 20 minutes of the starting time.
Air Pollution Standards define concentrations above which individual air pollutants are not to exceed when averaged over a period of time. Each of the air pollutants regulated by DEQ has a unique standard that is composed of a concentration and an averaging time. The API reduces these confusing combinations of standards to a single value index. The indexes generated can be used to view daily or seasonal changes in air pollution levels in time within an area or to compare the air pollution levels at different areas.
What exactly do that numbers mean?
Since the API represents the average air pollution over a period of time, DEQ has chosen to release two values each time. The first value represents the index averaged over the period from midnight to the hour of computation (10 a.m. or 4 p.m.) while the second value represents the index for all 24 hours of previous day.
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The Environmental Protection Agency developed a nationally standardized air pollution reporting system in the 1970s. This index is called the Pollution Standards Index because it is based on the National Ambient Air Quality Standards for air pollutants. Since the index is based on the standards and the standards in turn are based on health effects, the index is a health based index. Other indices that have been used in other areas of the county are based on visibility reduction or other, non-health based measurements.
The principle advantages of the nationally standardized index is 1) it allows comparison of air quality in various parts of the country and 2) is allows consistency in reporting from different areas in the country even when computed by different air pollution control agencies.
DEQ is required by the Clean Air Act to publish an air pollution index for areas with a population over 500,000. The index must be published on working days and at least once per day.
In an effort to provide better information to the citizens of Oregon, the API is generated for five major population centers in Oregon year round. In addition, some smaller cities have an API computed (sometimes by their own city staff) during times of the year when air pollution levels can become high as a result of home heating with wood. Normally these cities couple the local air pollution index with a wood stove advisory asking citizens to curtail wood stove usage on days when the projected index shows poor air quality.
The API is computed daily at 10 a.m. and 4 p.m. The program that computes the API starts by obtaining the latest pollution levels (hourly averages) from computerized data logging equipment connected to air pollution monitoring equipment around the state. Since the collection of the data is done using dial-up telephone connections, busy connections as well as malfunctioning data collection systems can slow down the process.
After the data collection phase is complete, the index is computed for each of the target areas and those values are stored in a file that is used to update DEQ's API database on the mainframe computer. The API is then uploaded onto the DEQ Network so that it is available to staff. Next the API information is routed to the National Weather Service office at the Portland Airport where it is in turn routed to the AFOS system to become part of the nationally available weather information. Also at that point it is routed to various news services in the state using the Oregon Weatherwire circuits.
Finally a revision to the DEQ web page is created and the updated web page containing the most recent data is uploaded to this web site.
CAUTION: The data contained in the air pollution reports on this site are taken from delicate air pollution monitoring equipment whose accuracy has not been verified by the time the report is made. It is possible that instrument calibration drift or other malfunctions could compromise the accuracy of the data being reported. Final monitoring results which are maintained by DEQ must pass stringent quality assurance requirements and are not available until at least six weeks after the monitoring data is received.
The National Ambient Air Quality Standards are a complex mixture of concentration limits for air pollutants when measured over specified time intervals. Unlike many measurements, instantaneous measurements of air pollutants is not very useful in determining the impact on human health. Therefore the standard or limits defined for air pollutants have an averaging period associated with them. The following table lists the short term standards.
| Pollutant | Standard Level | Averaging time |
| Carbon Monoxide | 9 parts per million | 8 hours |
| Particulate (10 micron) | 150 micrograms/cubic Meter | 24 hours |
| 50 micrograms/cubic meter | annual | |
| Ozone | 0.12 parts per million | 1 hour |
| Sulfur Dioxide | 0.5 parts per million | 3 hours |
| 0.14 parts per million | 24 hours | |
| 0.03 part per million | annual | |
| Nitrogen Dioxide | 0.053 parts per million | annual |
The API reduces these different averaging times, values and units of measure to a single number between 0 and 500. In this scale, 0 represents zero concentration of the pollutant, 100 represents the Standard Level averaged over it's averaging time, 200 represent the Alert level, 300 represent the Warning level, 400 represents the Emergency Level and 500 represents the Significant Harm Level. Alert, Warning and Emergency Levels are defined in the Oregon Air Pollution Emergency Action Plan which is Oregon Revised Statue 340.23. The Significant Harm level is defined by the Environmental Protection Agency as the level that causes "significant and imminent harm to the general public."
| Pollutant | Alert | Warning | Emergency | Significant Harm | Units of Measure |
| Particulate | 376 | 421 | 501 | 600 | micrograms/cubic meter |
| Carbon Monoxide | 16 | 31 | 41 | 50 | part per million |
| Ozone | 0.21 | 0.41 | 0.51 | 0.6 | parts per million |
| Sulfur Dioxide | 0.31 | 0.61 | 0.81 | 1.0 | parts per million |
| Nitrogen Oxides | 0.16 | 0.31 | 0.41 | 0.50 | parts per million |
| API | 200 | 300 | 400 | 500 | no units |
For each pollutant measurement sites in an area, a sub index is computed for each pollutant measured. For each of the subindexes measured in the area, the highest subindex is reported as the API for that area. Along with the value, the pollutant responsible for that value and the general location of the responsible measurement is reported. In addition, an assessment of the general air quality based on the reported API is also reported. The assessments along with their associated API ranges are
|
Good |
0-50 |
|
Moderate |
51-100 |
|
Unhealthful |
101-200 |
|
Very Unhealthful |
201-300 |
|
Hazardous |
301-500 |