Air quality
Southern California has some of the worst air in the country.
The American Lung Association has named Los Angeles the most ozone-polluted city in the country in 26 of its 27 annual reports.
A year of air
Southern California air, one day at a time.
Each dot is an air monitoring station. Colors follow the EPA air quality index.
- 35days when every monitor on the map read good
- 163days when a monitor read unhealthy for sensitive groups or worse
- No. 1Los Angeles ranks first in the U.S. for ozone pollution, per the American Lung Association
The highest reading from any pollutant at each station.
- 0Good
- 51Moderate
- 101Unhealthy for sensitive groups
- 151Unhealthy
- 201Very unhealthy
- 301Hazardous
U.S. EPA Air Quality System, 2024. Terrain: Mapzen. Roads: © OpenStreetMap contributors.
Playing the worst months on a loop: June to October.
Each square is one day, colored by the worst reading on the map. Pick a day, or press play.
Indoors
Fine particles are about 30 times narrower than a hair.
- 90%
- of an average American’s time is spent indoors.
- 10 µm
- Particles this size and smaller can get deep into your lungs.
- 0.3 µm
- The smallest particles a MERV rating measures, about 230 times narrower than a hair.
A ducted system pulls the air in your home through its filter each time the blower runs. The filter’s rating decides how many particles go back into the room.
Filters
MERV 1 to 16: what each rating catches.
MERV rates a filter by the size of the particles it stops. A higher number catches smaller particles and resists airflow more. Move the slider.
An illustration built from the minimum efficiencies in ASHRAE Standard 52.2. Real filters vary. A standard filter catches particles. It does not remove ozone, which is a gas.
MERV 1–4
Large debris
Over 10 µm
Pollen, dust mites, carpet fibers.
Basic disposable panels and window AC units. They protect the equipment more than the air.
MERV 5–8
Mold and dander
3 to 10 µm
Mold spores, pet dander, hair spray, dust.
Pleated filters found in many homes.
MERV 9–12
Fine dust
1 to 3 µm
Car exhaust, humidifier dust, lead dust, Legionella.
Rated superior residential.
MERV 13–16
Smoke and bacteria
0.3 to 1 µm
Bacteria, sneeze droplets, cooking oil, most smoke.
Used in hospitals. The EPA says most systems can take a MERV 13.
The EPA suggests a filter rated at least MERV 13, or the highest rating your system can handle, and says a technician can confirm what that is.
Find out what your system can take.
A higher rating also resists airflow more, and not every system can handle one. Air Plus checks the filter, return-air path, and ventilation before recommending a change.