Derry, Pennsylvania 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 Derry right now. All Pennsylvania warnings.

Good

Nearest monitor

Greensburg, 11 miles away (site 421290008)

Index measured

22 · Good

Measured at

Fri, 10:00 PM EDT

Fine particles

4 µg/m³

Ozone

17 ppb

Reporting area

Johnstown, PA, 20 miles away

Reported by

Pennsylvania Dept. of Environmental Protection

Area index

31 · Good

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

Pennsylvania Dept. of Environmental Protection's own forecast for Johnstown, written by a forecaster rather than read off a model.

Written by Pennsylvania Dept. of Environmental Protection for Johnstown and filed with AirNow.

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 33, Good, around Sat, 11:00 AM EDT, from the run issued Fri, 8:00 AM EDT. 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 Hazard Mapping System analysts drew light smoke over Derry in satellite imagery today (Fri, 8:00 AM EDT to Fri, 11:00 AM EDT). That is smoke seen from above; it is not always smoke at ground level.

NOAA’s model forecasts no measurable smoke near the ground here over the next two days.

Smoke on the radar over Derry

Good

Air quality is satisfactory, and air pollution poses little or no risk.

Who is affected

Nobody is expected to be affected.

What to do

It is a good day to be outside.

Index range

0 to 50

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.

• Loyalhanna, PA3 miles
• Latrobe, PA4 miles
• Lawson Heights, PA6 miles
• Blairsville, PA7 miles
• Ligonier, PA7 miles
• Waterford, PA9 miles
• Black Lick, PA11 miles
• Greensburg, PA13 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.