Clearing the Air: Cheap, Reliable Air Monitoring at Home

Clearing the Air: Cheap, Reliable Air Monitoring at Home

By Tom Frantz

Personal air monitoring has been gaining popularity in the San Joaquin Valley. Many people have recently installed a fine particulate monitor from a company called PurpleAir. At a cost of around $200, these monitors give an excellent picture of the air quality surrounding a home, business or neighborhood. A couple dozen of these have shown up in the Fresno and Bakersfield areas. Other types are also available at varying costs.

Most of the people installing these monitors are concerned about the air quality for personal health reasons. There should soon be many more of them as residents find out how cheap they are and how easy to install. They also benefit nearby neighbors. Any person can use the data from these monitors by checking the map at The Air Quality Index for each monitor’s measured pollution level is posted on the map and updated every 80 seconds. Real time information is invaluable in protecting your health if you have breathing difficulties and need to go outside.

These private monitors only measure particulates. They do not measure ozone pollution. But, fine particulate matter is our most serious type of pollution in regard to the severity of the health impacts.

For ozone, most people still depend on air district monitors. The air district monitors, for both ozone and particulates, are not real-time monitors. They only update once per hour (about 20 minutes after the hour) and they only give the average reading of the previous hour. Seeing an actual number measuring current pollution levels every 80 seconds is far superior to getting a single hourly reading that is already an hour old. Cheaper ozone monitors for personal use should be available in the near future.

The personal monitors have proven extremely useful during recent smoke events from wildfires. Local smoke levels can vary greatly with the wind direction. A city might be simultaneously heavily polluted on the north side and clear to the south. The situation can change in just a few minutes. The air district air monitoring system does not give information about a rapidly changing situation.

During the winter, when PM2.5 levels are generally much higher, there are specific times that are the worst. As hourly temperatures rise during the day, PM2.5 levels drop off. They worsen again after dark. To find out if it is safe to go outside to work or exercise, a personal monitor can give accurate, up-to-the-minute localized information.

The air district has claimed its $25,000 monitors are more accurate. It has little respect for these cheap personal monitors. In fact, the air district refused to cooperate with a program where the South Coast Air District (Los Angeles) proposed, through a grant, to work with local residents on installing these monitors at a greatly subsidized cost and training them on their use. The South Coast Air District quietly withdrew its proposal when the air district said no thanks.

In reality, the PurpleAir monitors have shown over and over that they correspond closely to the official monitors, especially in the relative ups and downs of pollution levels. They might not always read the exact same level of pollution, even when side by side, but the changes in pollution levels are accurately measured.

Our air district wants to have control over air quality information. The air district even wants to set its own Air Quality Index (AQI) numbers that tell the public how bad the air is. For example, an ozone reading of 72 parts per billion will show moderate air quality on the air district’s scale but unhealthy for sensitive groups on the official EPA (U.S. Environmental Protection Agency) scale. The air district is the only entity in the world using its own AQI scale.

The air district also wants the sole ability to decide if the air is safe to breathe. The air district basically assumes that if the air is clean at its official monitoring location, then it must be clean everywhere within 20–50 miles. Citizen air monitoring will show whether that is a valid assumption.

Citizen monitoring will also show hotspots that might be localized. Living close to a freeway and next door to an industrial source of pollution could present significantly worse pollution levels than at a site just one mile away. Smoky wood stove burning in one neighborhood might be far more prevalent than somewhere else a few miles away.

This citizen monitoring should also prevent the air district from cleaning up pollution that is nearby to its monitors but not cleaning it up elsewhere. The air district has proposed doing exactly that with a hotspot strategy in its new PM2.5 cleanup plan.

The air district always predicts the average pollution levels for the next day. This prediction is often shown during the evening weather forecasts. But these predictions are even less reliable than the weather forecasts. They seem to be wrong nearly half the time. This is just another reason to have a personal monitor telling you the actual pollution levels in your own neighborhood without delay.


Longtime clean air advocate Tom Frantz is a retired math teacher and Kern County almond farmer. A founding member of the Central Valley Air Quality Coalition (CVAQ), he serves on its steering committee and as president of the Association of Irritated Residents. The CVAQ is a partnership of more than 70 community, medical, public health and environmental justice organizations representing thousands of residents in the San Joaquin Valley unified in their commitment to improving the health of Californians. For more information, visit


  • Community Alliance

    The Community Alliance is a monthly newspaper that has been published in Fresno, California, since 1996. The purpose of the newspaper is to help build a progressive movement for social and economic justice.

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