Stevenson Ranch, California Air Quality

An Air Quality Alert is issued by the National Weather Service on behalf of a state or local agency when pollution is expected to reach a level that harms health. An Air Stagnation Advisory means the air will not move enough to clear what is already in it.

None are in force near Stevenson Ranch right now. All California warnings.

Unhealthy for Sensitive Groups

Nearest monitor

Santa Clarita, 3 miles away (site 060376012)

Index measured

101 · Unhealthy for Sensitive Groups

Measured at

Sun, 4:00 PM PDT

Fine particles

15.5 µg/m³

Ozone

78 ppb

Reporting area

Santa Clarita Vly, CA, 3 miles away

Reported by

South Coast AQMD

Area index

101 · Unhealthy for Sensitive Groups

Measured, not modeled. AirNow observations are preliminary until the operating agency certifies them, which happens months later.

South Coast AQMD's own forecast for Santa Clarita Vly, written by a forecaster rather than read off a model.

NOAA’s National Air Quality Forecast Capability, bias-corrected against monitors, for this town’s own coordinate. The worst hour ahead is an index of 105, Unhealthy for Sensitive Groups, around Sun, 7:00 PM PDT, from the run issued Sun, 5:00 AM PDT. This is a model, not a measurement.

Fine particles in micrograms per cubic meter, ozone in parts per billion as an 8-hour average. The index for each hour is EPA’s: the ozone figure is already the 8-hour average the ozone index is defined on, and the particle figure is run through EPA’s NowCast, which is how an hourly PM2.5 concentration becomes an index.

NOAA’s analysts have not drawn smoke over Stevenson Ranch in satellite imagery today.

NOAA’s model forecasts near-surface smoke peaking at 0.5 µg/m³ around Sun, 4:00 AM PDT.

Smoke on the radar over Stevenson Ranch

Unhealthy for Sensitive Groups

Members of sensitive groups may experience health effects. The general public is less likely to be affected.

Who is affected

People with asthma or other lung disease, people with heart disease, children, older adults, and anyone active outdoors.

What to do

Sensitive groups should make outdoor activity shorter or easier, and take more breaks. Watch for coughing or shortness of breath.

Index range

101 to 150

Category descriptions are the Environmental Protection Agency’s own.

What these numbers are. An index beside a monitor’s name is a measurement, published hourly by AirNow and preliminary until the operating agency certifies it. A category for today or tomorrow is a state or local agency forecaster’s own forecast for a reporting area. An hourly index is NOAA’s air quality model on a five-kilometer grid, not a reading from any instrument. Where a town has no monitor within reach, only the model figures appear, and the page says so.

The nearest towns with a page of their own, closest first.

• Santa Clarita, CA2 miles
• Valencia, CA4 miles
• Val Verde, CA6 miles
• Canyon Country, CA6 miles
• Castaic, CA7 miles
• Sylmar, CA9 miles
• Chatsworth, CA9 miles
• Santa Susana, CA11 miles

Observations and daily forecasts from AirNow, the US Environmental Protection Agency’s program with NOAA, the National Park Service, NASA, tribal, state and local agencies. Hourly forecasts from NOAA’s National Air Quality Forecast Capability. Smoke analysis from NOAA’s Hazard Mapping System. Alerts from the National Weather Service. Index categories and breakpoints are EPA’s, as revised in 2024.