Air Monitoring & AQI

What is the Air Quality Index (AQI)?

Air Quality Index (AQI) numbers come from air monitors that measure the concentration of different kinds of pollution in the air. These numbers provide a quick way to determine whether the air is safe to breathe. The lower the number, the cleaner the air. Alternatively, higher numbers indicate higher levels of air pollution.

Learn more about AQI (https://www.airnow.gov/aqi/aqi-basics/)

What kinds of pollutants does the AQI measure?

Typically, you’ll see AQI for particulate matter (PM 10 and PM2.5) and ozone.

Particulate matter exposure can cause a range of health effects, from eye and throat irritation to asthma attacks and worsening of heart and lung disease, including asthma.  Fine particulate matter (PM2.5) is small enough to get deep into the lungs and the tiniest, ultrafine particles can pass directly into the bloodstream, increasing the risk of heart attack or stroke.

Ozone can damage the tissues in the respiratory tract, causing inflammation and irritation, resulting in symptoms such as coughing, chest tightness, shortness of breath and worsening of asthma symptoms.

 Some people are more impacted by air pollution than others. Sensitive groups include children, seniors, pregnant people, people with asthma or other respiratory conditions, and people suffering from heart conditions. People in these sensitive groups should be especially vigilant and take extra precautions to protect their health.

If you are experiencing health concerns or having trouble breathing, it is best to call your medical provider for advice.

How accurate is the AQI?

The reliability of the AQI reading depends on the accuracy of the air monitors. Some AQI readings are based on regulatory-grade air monitors, while others are based on low-cost sensor data (e.g., Purple Air). The regulatory-grade air monitors used to calculate AQI are extensively calibrated and maintained to rigorous standards; CARB is confident that these AQI readings are accurate.

Most websites or mobile apps use different symbols to differentiate between air monitors and low-cost sensors on their maps. Be sure to check the map’s legend to understand what kind of device is providing the AQI.

Does the AQI include air toxics?

No. Toxics are measured using different monitoring equipment.

However, some toxics – including those known to be found in burned residential buildings (e.g., lead, chrome) – are carried through the air by sticking to particulate matter, so tracking the AQI for PM2.5 can help minimize your exposure to those toxics too.

The methodology for collecting, analyzing and reporting air toxics data is complicated and time-intensive, meaning it takes days or weeks to report air toxics data as compared to minutes or hours for particulate matter data.

The South Coast Air Quality Management District has more information on its air toxics monitoring program in the Los Angeles area on its 2025 Wildfire Response (https://www.aqmd.gov/2025-wildfire-response) webpage.

What are some trustworthy AQI sources?

There are two primary sources CARB recommends using to check the AQI, particularly as it relates to wildfire smoke. While the AQI information is the same on both platforms, other features differ slightly. You do not need to use both – pick the one that works best for you.

1. CARB’s California Smoke Spotter mobile app. In addition to AQI for PM2.5 from regulatory monitors, the app includes Purple Air sensors for relative, real-time information, as well as 72-hour smoke and AQI forecasts. It also shows Clean Air Centers where people can get relief when air quality deteriorates. Free to download on the App Store (https://apps.apple.com/app/id1531391671) or Google Play (https://www.aqmd.gov/home/air-quality/air-quality-advisories?id=com.prescribedfiresapp).

2. The AirNow Fire and Smoke Map (https://play.google.com/store/apps/details) from US EPA also includes AQI from regulatory monitors and Purple Air sensors, as well as Smoke Outlooks issued by the U.S. Interagency Wildland Fire Air Quality Response Program during large wildfire events.

What should we look for when we check the AQI?

In addition to looking at the AQI numbers, you’ll see colors that represent AQI ranges, established by US EPA. This chart explains what they mean and provides general activity guidance for each category.

What about sensitive groups? Are there people who should be checking the AQI more often because they’re more susceptible to health impacts from smoke and poor air quality?

Yes. Some people are more impacted by air pollution than others. Sensitive groups include children, seniors, pregnant people, people with asthma or other respiratory conditions, and people suffering from heart conditions. People in these sensitive groups should be especially vigilant and take extra precautions to protect their health. 

If you are experiencing health concerns or having trouble breathing, it is best to call your medical provider for advice.

The air near me is hazy and looks bad. How can the AQI be Good/Moderate?

There could be several reasons for this:

• The air quality website or app you’re using may be reporting AQI for a pollutant other than particulate matter (PM). Fine particulate matter (PM2.5) is the primary pollutant found in wildfire smoke and ash and poses a serious health risk to the public. On most AQI maps, you can click on an icon to see what pollutant it’s measuring.
• There may be a delay between current conditions and the AQI reported on a website or app (typically 1 hour behind). 
• Low-cost sensors like Purple Air tend to be less accurate, but do provide a real-time, relative picture of local air quality. For example, if you see a group of sensors in your neighborhood are all red on the map, the actual AQI data they’re providing may not be spot-on, but it’s probably safe to assume that there is PM in the air.
• The smoke or haze you see may be high in the air, and while conditions look severe, ground-level concentrations (where we’re actually breathing) may be lower.
• Some apps may report AQI information from a monitor or sensor a few miles away from your location, which may not reflect hyperlocal air quality conditions.

Wildfire Smoke 

What air pollutants are typically found in wildfire smoke?

Wildfires produce a range of harmful air pollutants, though particulate matter (PM) is the main pollutant in wildfire smoke.

Wildfires that burn structures and vehicles are known to produce a variety of toxic air pollutants, in addition to particulate matter. Wildfires also release greenhouse gas emissions that contribute to climate change, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). 

How long until we know what toxics were in the wildfire smoke?

The methodology for collecting, analyzing and reporting air toxics data is complicated and time-intensive, meaning it takes days or weeks to report air toxics data as compared to minutes or hours for particulate matter data.

Thousands of buildings have burned in the Southern California wildfires – can similar fires in the past tell us anything about what could be in the smoke or air this time?

In 2018, the Camp Fire in Paradise burned nearly 19,000 buildings. In addition to dangerous levels of particulate matter, elevated levels of lead and zinc were detected, as well as calcium, iron and manganese. Smoke containing these metals traveled more than 150 miles. CARB’s Camp Fire Air Quality Data Analysis (https://www.airnow.gov/aqi/aqi-basics/) includes information on the levels of pollutants, when they spiked, as well as information on general health impacts associated with the different pollutants.

The Camp Fire was different in many ways from the Southern California wildfires in January 2025, but what we found in the smoke in Northern California in 2018 is an example of what we could see once the data from the recent fires is collected, analyzed and validated.

Protecting Yourself from Smoke and Ash

What does wildfire smoke do to your health? Who is most at risk?

Health problems related to wildfire smoke exposure can be as mild as eye and respiratory tract irritation and as serious as worsening of heart and lung disease, including asthma, and even premature death.

Wildfires produce a range of harmful air pollutants, from cancer-causing substances to tiny particles that can aggravate existing health problems and increase the risk of heart attack or stroke. Fine particulate matter (PM2.5) is small enough to get deep into the lungs and the tiniest, ultrafine particles can pass directly into the bloodstream.  

Some people are more impacted by air pollution than others. Sensitive groups include children, seniors, pregnant people, people with asthma or other respiratory conditions, and people suffering from heart conditions. People in these sensitive groups should be especially vigilant and take extra precautions to protect their health. 

If you are experiencing health concerns or having trouble breathing, it is best to call your medical provider for advice.

Should I wear a mask when I’m outside? What kind? For how long?

If you are unsure if you should wear a mask, we recommend asking your medical provider.

In general, if the AQI is Good or Moderate (green or yellow), it’s probably safe for most people to be outside without a mask (see AQI activity guidance above). 

However, if you smell smoke, see ash being blown around in the air, or experience nose or throat irritation, you may want to wear a mask outside, even when the AQI is Good or Moderate.

Adults who are outdoors in areas with smoke, or where ash is disturbed, should wear a NIOSH-certified N95 respirator mask, or a P-100 respirator. People with existing respiratory, lung or heart conditions should limit their exposure by staying indoors. Since wearing a respirator can make it harder to breathe, people with lung or heart conditions should check with their doctor before using one.

If you purchase N95 masks, make sure they are NIOSH-approved (https://apps.apple.com/app/id1531391671). Choose a size and model that fits your face and has no gaps. Test it by doing a seal check (https://recovery.lacounty.gov/debris-removal/hazardous-material/). 

The California Department of Public Health answers some Frequently Asked Questions about N95 respirators on its website (https://www.cdph.ca.gov/Programs/EPO/Pages/Wildfire Pages/N95-Respirators-FAQs.aspx).

How do we protect children from smoke or windblown ash, if they can’t wear a N95 mask?

Children are especially vulnerable to health effects during wildfires due to their developing lungs and other factors. Some teens may be able to wear a N95 mask, but only if it fits their face snugly and creates the proper seal as mentioned above.

Children and other sensitive groups should remain indoors with windows and doors closed when the AQI reaches Unhealthy (red) levels. Children who are considered more sensitive (e.g. those with asthma or underlying respiratory conditions) should limit outdoor activity when the AQI reaches levels considered Moderate (yellow) or Unhealthy for Sensitive Groups (orange). Use the activity guidelines provided in the AQI chart above to make the best decision for your family.

Follow the tips below for reducing smoke exposure in your home. If you must bring your child outside when the air quality is poor, minimize exposure by limiting exercise and time spent in the bad air.

Consider relocating sporting events or gatherings to a location where the air is cleaner and the AQI is good.

How do I protect my pets from smoke?

This factsheet (https://www.airnow.gov/sites/default/files/2021-06/protect-your-pets-from-wildfire-smoke.pdf)from U.S. EPA provides information on keeping your pets safe before and during a wildfire.

How do I protect my family from smoke if we have to evacuate?

It’s easy to forget about smoke when evacuating from wildfires. There are several ways to protect yourself when traveling away from a fire. 
•    Stay inside your vehicle with windows and doors closed.
•    Run the air conditioning with Recirculate turned on.
•    Wear an N95 mask in your vehicle and at emergency shelters if they don’t provide filtered air.
•    For those with asthma or respiratory conditions, bring inhalers and medication.
•    If possible, try to evacuate to an area with better air quality.

What are Clean Air Centers? How do I find one near me?

Clean Air Centers provide a safe place with filtered air where people can go when there is poor air quality, including periods of intense wildfire smoke.

The California Clean Air Centers Map (https://ww2.arb.ca.gov/cleanaircenters) was created by CARB and local air quality control districts to provides information about the location and services offered at Clean Air Centers in local communities. Clean Air Centers are also shown on the California Smoke Spotter mobile app, which is free to download on the App Store (https://apps.apple.com/app/id1531391671) or Google Play (https://www.aqmd.gov/home/air-quality/air-quality-advisories?id=com.prescribedfiresapp).

Resources

For more information on protecting yourself from wildfire smoke, visit Smoke Ready California (https://ww2.arb.ca.gov/smokereadyca) (also available in Spanish (https://ww2.arb.ca.gov/es/smokereadyca)). It provides instructions on how to reduce smoke exposure inside your home, including how to create a Cleaner Air Space and how to build a DIY box fan air cleaner.

For more information on California’s ongoing response to the Los Angeles fires, visit ca.gov/lafires (https://www.ca.gov/lafires/).