HEALTHYBUILDINGSCIENCE is committed to facilitating the accessibility and usability of its website,, for everyone. HEALTHYBUILDINGSCIENCE aims to comply with all applicable standards, including the World Wide Web Consortium's Web Content Accessibility Guidelines 2.0 up to Level AA (WCAG 2.0 AA). HEALTHYBUILDINGSCIENCE is proud of the efforts that we have completed and that are in-progress to ensure that our website is accessible to everyone.

If you experience any difficulty in accessing any part of this website, please feel free to call us at (415) 785-7986 or email us at [email protected] and we will work with you to provide the information or service you seek through an alternate communication method that is accessible for you consistent with applicable law (for example, through telephone support).

Request an Inspection

Call us at (415) 785-7986 or click the button below to schedule your building health assessment.

Request a Site Visit

Sign up for our Quarterly newsletter

Subscribe to our e-mail newsletter to receive helpful updates and articles from Healthy Building Science.

Sign Up For Newsletter

We value your privacy.
Your email is never shared or sold.

Air Quality Index (AQI) and You

by / Wednesday, 06 February 2019 / Published in Environmental Testing, News

Air Quality Index (AQI) and You

During the 2018 Paradise Fire smoke wave, many in the Bay Area obsessively checked online for air quality information and updates. Here is an overview of a handful of real-time air quality websites I found helpful and how they compare. Keep in mind that climate change plus newer and cheaper monitoring equipment means that air quality information sources can change quickly. Air Quality Index (AQI) sites use a map to show the AQI number for an area. But what does this AQI number mean and why do different sites report different numbers?


Here is a short summary of the sites I used around the San Francisco Bay during the Paradise Fire.

Air Quality Info My top two choices for air quality: EPA and

Runners up included Breezometer app and my native iphone weather app.

EPA Air Quality Index (AQI) Map Purple Air Air Quality Index (AQI) Comparison to EPA Map
Pros: most widely used. High quality sensor (~$75,000 each)

Cons: fewer sensors can misrepresent microclimates, refreshes every 2 hours. Site overwhelmed with web traffic during smoke wave.

AQI number tends to be lower

Pros: Near instant readings, Many more sensors to show more detailed levels of air quality. Cons: Sensors not as accurate in higher concentrations (~$250 each).

AQI number tends to be higher


San Francisco Bay Area AQI Map San Francisco Bay Area Air Quality Map View and AQI Comparison
EPA Airnow Fire Shows 2.5PM monitors for The Bay Area. Note only one for San Francisco Purple Air Nearly 50 monitors in San Francisco


iphone weather app Breezometer app
iPhone Air Quality rating comparison BreezoMeter iPhone Air Quality App Comparison
Pros: Super easy to access.

Cons: The source of this info has not been disclosed by Apple. I speculate it is based on EPA data. Slower to refresh than

Pros: Breezometer app is easy to use. One great feature is the ability to compare air quality at different saved locations. Shows 2.5PM counts in ug/m3.

Cons: the app stopped working at times during the smoke wave. They developed their own version of AQI, so hard to compare numbers to other sites.


FYI here are some other sites I used to track fire and smoke during the Paradise Fire:

Smoke and Fire Info

California Smoke Information Blog

California Wildfires traffic/fire Map

Smoke from Wildfires Map

San Francisco Dept of Emergency


What is the Air Quality Index?

What is meant by AQI – Air Quality Index?

AQI is a color-coded, simplified index for reporting daily air quality. The EPA’s AQI index can help inform questions during smokey/smoggy days such as, “Should I keep my asthmatic child home from school?”, “Will the soccer game be canceled” or “Do I need to wear a mask?”

“It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide.” source

What is Particulate Pollution – specifically 2.5 PM?

If the sky looks hazy, that is particle pollution, a mixture of solid particles and liquid droplets found in the air. Some particles are large enough to be seen with the naked eye; others are so small they are measured using an electron microscope. At Healthy Building Science we count 2.5 PM particulate pollution with our Lighthouse Laser Counter. These particles can be made up of hundreds of different chemicals.

Particle Counter Air Quality Monitoring and AQI with Dog in Car Particle Counter Air Quality Monitoring and AQI Comparison
Driving south in our RV, searching for cleaner air during the Paradise Fire. Monitoring particulate air pollution on the road, with our Lighthouse Particle Counter during the Paradise Fire smoke wave.

Fine particles (PM2.5) are very bad for your health, triggering or worsening chronic diseases such as asthma and heart attack, causing 4.2 million premature deaths worldwide per year in 2016. Read more from the  World Health Organization.  They are considered to be more harmful than larger particles because they penetrate the lung barrier to enter directly into the blood system.  China recently lowered 2.5PM particle pollution in urban areas, residents are now expected to live 3.3 years longer! Source

All 2.5 particulate pollution is harmful to human health and smoke from burning buildings contains additional harmful pollutants compared to a forest fire. The AQI does not differentiate types of particulate pollution. The chemical makeup from wood smoke vs smoke from a burning car or hardware store can be significant. Smoke from burning buildings in Paradise, CA contained more harmful pollutants, such as flame retardants, plastics, and asbestos, than the smoke from the following forest fire. Weather Underground is recommending Purple Air monitors to track “deadliest type of air pollution”, 2.5PM particles.

US EPA PM2.5 AQI Monitoring Building Science Air Quality Monitoring for San Francisco Bay Area
If you really want to geek out on the numbers – here is a table comparing the AQI number to 2.5 PM counts. At Healthy Building Science we have a number of gadgets to monitor 24-hr Average 2.5 PM concentration.


Real-Time Air Quality Maps

On day 7 of the Paradise Fire, the San Francisco Unified school district canceled school as the AQI hit 235  – the PURPLE Very Unhealthy Level.  BUT was showing AQI in the 400’s.  

Current AQI Map from Governmental Map Current Air Quality Map from non-Governmental source
November 15, 2018 November 15, 2018


So why the difference in AQI numbers at and Purpleair?  The most obvious difference is that the EPA’s AIQ number includes 5 major air pollutants whereas Purpleair is only monitoring 2.5PM particulate pollution. Both use proprietary algorithms to calculate/ average out their AIQ numbers.  I found it best to use AIQ as a way to compare air quality over time and at different locations and I now resist the urge to narrow down to specific AIQ readings.

Northern Sonoma County Air Pollution Control District published a detailed guide and in depth comparison of airnow vs Purple air.

Stepping back from the numbers is all fine and good unless you are a decision maker for other people such as elementary school principals at Sonoma County School. They have been instructed:  

  • On days with questionable air quality, superintendents shall check at 5:00 am.
  • If the Air Quality Index (AQI) is listed at 275 or above, districts may cancel classes.

This public school district chooses NOT to use the EPA and instead use Purpleair.  This is a time of great change with climate chaos and affordable, emerging technologies.

  • Great coverage of Sonoma County School’s decision on this wine country parent’s blog.
  • Great overview of government vs private sources of air quality data at

Sonoma County School Air Quality Guidelines. source


Sonoma County Schools Air Quality Guidelines

I appreciate the Sonoma County Office of Education for taking a stand and publishing this guide. I plan to use it during future smoke waves. 

Check out my blog on DIY Box Fan Filters.

Let’s wrap up this AQI ramble with the EPA’s Actions People Can Take to Reduce Particle Pollution:

  • Conserve electricity
  • Use dry, seasoned wood for fireplaces and stoves
  • Carpool, use public transportation, bike, or walk when possible
  • Avoid idling car engines for long periods of time
  • Keep car tires properly inflated
  • Maintain car, boat, and other engines to ensure maximum fuel efficiency
  • Buy an electric car (I added this last one)

Written by Anne-Lise Breuning, Industrial Hygienist and Environmental Inspector for Healthy Building Science.


Healthy Building Science is an environmental consulting firm which provides indoor air quality testing services for commercial, multi-family buildings, offices, industrial and manufacturing workplaces, hospitals and medical facilities, and single-family homes in the greater San Francisco Bay Area and all of Northern California.

We would be pleased to become your go-to air quality consultant and help you with any of your air quality lab testing or air quality monitoring needs.

Please call 415-785-7986 or complete this online form today!


One Response to “Air Quality Index (AQI) and You”

  1. Antoniowam says :

    The shift has coincided with rising temperatures and changing weather patterns, as a result of anthropogenic human-influenced climate change. Environmental scientists expect the number of burnt acres per year to continue to rise over the coming years, presenting a growing challenge for the Bay Area and its air quality. 3 Generally, air quality in San Francisco is at its best in the spring, as temperatures gradually warm and the forest undergrowth is still wet from the frequent rains of the winter months.

Leave a Reply



Subscribe to our e-mail newsletter to receive helpful updates and articles from Healthy Building Science.

You have Successfully Subscribed!