How is AQI calculated? Here’s how you can monitor your local air quality in California
As fire season lengthens and excessive heat plagues California more often, checking air quality goes hand-in-hand with your local weather forecast.
External everyday factors such as vehicle fuel emissions, gas from industrial facilities and wildfires affect daily pollution. To measure this, the U.S. Environmental Protection Agency calculates a daily air quality index, known as the AQI, that’s presented on a scale of zero to 500.
“California has a lot of micro climates and a lot of unique topology which really impacts where the air travels and where the pollution accumulates,” said Keith J. Bein, associate professor and air quality researcher at University of California, Davis. “What one neighborhood is experiencing can be vastly different than what’s happening down the road.”
To calculate accurate AQI that is specifically representative to California’s cities and rural communities, distributed sensor networks are put into place to gather data.
What contributes to poor air quality?
The EPA monitors ground-level ozone pollution, particle pollution, carbon monoxide, sulfur dioxide, lead and nitrogen dioxide. The agency is required to monitor these “criteria pollutants” under the Clean Air Protection Act.
Each criteria pollutant can uniquely contribute to harmful health effects and negative environmental consequences.
According to AirNow, a federal partnership with the EPA, the U.S. National Oceanic and Atmospheric Administration and other government entities, ozone is naturally present in the earth’s atmosphere. However, pollutants such as ground-level ozone, which are emitted through vehicles, contribute to poor air quality and can “irritate the respiratory system.”
“Good ozone” occurs naturally in the upper atmosphere and protects us from harmful sun rays, according to the EPA. Its counterpart, ground-level ozone, is the harmful pollutant that “the main ingredient” in smog. Ozone is typically more prevalent in the heat when air is stagnant.
Particle pollution is often a result of wildfires. A study published in the AirNow discovered that “wildfires contribute 15 to 30% of atmospheric primary fine particulate matter emissions in the Untied States”.
PM2.5, also known as particle pollution, can be spotted in the air. The small floating particles can sometimes create a foggy appearance.
“Emissions of fire pollution is the biggest concern,” said UC Davis professor Qi Zhang, who teaches in the Department of Environmental Toxicology and conducts research on air pollution.
What is the AQI chart?
The AQI chart is used to classify air quality levels using a formula and the criteria pollutant numbers. A number is calculated daily unless there is an extreme condition, such as a wildfire, when it’s updated more often.
Zhang said when air quality is stable, the EPA uses 12-hour averages to calculate an AQI.
During fire season, air quality is calculated in real time. Zhang said ozone levels are calculated hourly and PM2.5 is calculated every three hours.
The AQI chart is broken into six colors: green, yellow, orange, red, purple and maroon. Each color represents a range on the AQI chart from zero to 500, with zero being “satisfactory air quality” and 500 being “health warning and emergency conditions.”
How can you protect yourself from bad air quality?
The first step to staying protected from poor air quality is to stay informed with the most up-to-date AQI in your neighborhood. AQI scores are posted daily on AirNow or can be found in the weather app on your smartphone. If you don’t have access to either, news outlets also inform the public when poor air quality scores are underway.
Cities throughout California like Sacramento, Los Angeles and San Francisco all have air quality monitors throughout the city to track AQI and inform the community of air quality. For example, Sacramento Region Spare the Air will issue alerts to the community for poor air quality and urge residents to use less fuel.
In the event that the air quality in your neighborhood is not safe, try and avoid going outdoors as much as possible. In your house, shut all your windows and if you have access to an air purifier, use it. Another quick fix would be to switch your air filters in your home.
Staying home is not feasible for everyone, which is why if you are required to be outdoors during unhealthy air conditions it is strongly advised to wear an N95 mask.
Resources for your community:
Resources to compare air quality across the United States:
This story was originally published September 14, 2022 at 5:29 AM with the headline "How is AQI calculated? Here’s how you can monitor your local air quality in California."