Last Updated: 04/28/2019
The Air District maintains one of the most comprehensive air quality monitoring networks in the country, consisting of over 30 stations distributed among the nine Bay Area counties. This network measures concentrations of pollutants for which health-based ambient air quality standards have been set by the U.S. Environmental Protection Agency and the California Air Resources Board. The network also measures concentrations of various pollutants designated as Toxic Air Contaminants by the state of California.
How clean or polluted the air is and the level of health concern is in the Air Quality Index (AQI). The AQI categorizes air quality based on air measures collected from Department of Environmental Quality (DEQ) air monitors. The AQI provides real-time monitoring and alerts in response to changing air quality levels. The AQI accounts for five different pollutants, including: 1) ground-level ozone; 2) particle pollution (also known as particulate matter); 3) carbon monoxide; 4) sulfur dioxide; and 5) nitrogen dioxide. Of these, ground-level ozone and particulate matter are the most common and most concerning pollutants for outdoor physical activity. The AQI value for the day, is based on the 24-hour average concentration as established by the U.S. EPA, so hourly readings are only estimates. The one-hour average is meant to protect against acute exposure and the 24-hour average is meant to protect against more long-term exposure at lower levels. Both will impact your health.
- PM is usually measured in two size ranges: PM10 and PM2.5.
- PM10 refers to particles with diameters that are less than or equal to 10 microns in size (a micron, or micrometer, is one-millionth of a meter), or about 1/7 the diameter of a human hair.
- PM2.5, also called "fine particulates," consists of particles with diameters that are less than or equal to 2.5 microns in size. PM2.5 is a more serious health concern than PM10, since smaller particles can travel more deeply into our lungs and cause more harmful effects
During northern California's wildfire season, the Air District monitors general air quality in the Bay Area and will issue a health advisory if wildfire smoke appears to be causing elevated levels of particulate pollution in the region.
In addition to the AQI, you can use your own observations to determine the air conditions in your area. To do a visual inspection:
- Go outside.
- Face away from the sun.
- Determine the limit of your visible range by looking at objects at known distances (miles).
- Visible range is the point at which even high contrast objects totally disappear.
Low-cost air quality sensors are a relatively new technology that measure specific air pollutants, typically particulate matter and some gaseous pollutants, and cost much less than traditional air quality monitors. Since this emerging technology is still under development, little information exists on the quality of data that these sensors produce. In the United States, air quality has traditionally been measured according to standards established by the United States Environmental Protection Agency (EPA) using regulatory monitors that are designated as federal reference method (FRM) or federal equivalent method (FEM). These monitors cost tens of thousands of dollars and require significant infrastructure and trained personnel to operate, whereas, low-cost sensors may only cost a few hundred dollars and can be simple to operate. Low-cost air quality sensors cannot replace traditional regulatory monitors, but they do create new opportunities to increase and expand access to air quality monitoring and can play a part in tracking air quality.
PurpleAir Sensor FAQ
The PA-II Dual Laser Air Sensor uses laser beams to detect the particles going past by their reflectivity, like dust shimmering in a sunbeam. The PM 2.5 and PM 10 micro-gram weights are calculated from the counts. The displays points correlates with the Federal Environmental Protection Agency (EPA) Air Quality Index (AQI) scale. The AQI allows comparison for different pollutants with an easy to visualize color scheme. The values are averaged every 20 seconds versus the 24-hour average concentration as established by the U.S. EPA.
Most studies comparing Purple Air sensors to regulatory monitors have found Purple Air sensors report higher levels than regulatory monitors. Recognizing this discrepancy, Purple Air has added the ability to apply "Conversion" factors to their website map. AQandU applies to University of Utah and the Salt Lake City region. LRAPA applies to Lane Regional Air Protection Agency located in Springfield Oregon. There currently isn't a conversation formula established for this region.
- Wildfire smoke can make asthma symptoms worse. It can trigger asthma attacks. Symptoms of asthma include coughing, shortness of breath, wheezing and chest tightness. Even students without known asthma can have symptoms when exposure to unhealthy levels of wildfire smoke pollutions.
- Students with asthma should follow their Asthma Action Plan. This will help them decide if they need to take special precautions while engaging in outdoor activities. Athletes with asthma should have rescue inhalers readily available. Use should be as directed by their health care provider.
- Anyone experiencing symptoms should contact a health care provider.
- Call 911 in an emergency.