This post overlaps with a fuller one: How to Monitor Air Quality in LA, Indoors and Out.
Monitoring air quality in Los Angeles comes down to one number, the AQI, and two places to get it: the government map for your address and a neighborhood sensor for your street. Add a small indoor monitor and you know what you are breathing at home in Pasadena, CA or the valleys.
The AQI scale
The EPA's AirNow scale runs in six color-coded categories. Green 0 to 50 is good; yellow 51 to 100 is moderate; orange 101 to 150 is unhealthy for sensitive groups; red 151 to 200 is unhealthy, where AirNow says some of the general public may feel it and sensitive groups may feel it more seriously; purple 201 to 300 is very unhealthy; maroon 301 and higher is hazardous. It covers ozone, particle pollution (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. In LA, ozone is the summer afternoon problem in the inland valleys and PM2.5 is the wildfire-smoke problem in fall.
Where to check
- AirNow.gov or its app, by ZIP code.
- South Coast AQMD's current AQI map at aqmd.gov/aqimap, its app, which you can set to notify you at a level you pick, and its advisory emails, which you sign up for on aqmd.gov.
- Neighborhood sensors such as PurpleAir units for street-level trends. Compare them to the official map; they are not calibrated the same way.
At home
A consumer PM2.5 monitor at breathing height, away from the stove and windows, shows whether outdoor smoke is getting in. On bad days, the EPA's home air-cleaner guide recommends a MERV 13 filter or higher where the system can take one, running the HVAC fan so air keeps passing through it, closing windows, and running a portable HEPA cleaner sized by CADR for the room. If indoor readings stay high anyway, leaking attic ducts are the usual reason, and a whole-home purifier or a maintenance visit that checks the ducts is the next step.
The full guide: How to Monitor Air Quality in LA, Indoors and Out.
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Written with AI assistance by Boost Services, Heating and Cooling team, and reviewed by our licensed technicians before publishing. Boost Services Heating and Cooling, C-20 #1119892.