# Pennsylvania air quality today — live AQI by metro > Source: https://breathecheck.com/air-quality/us/pennsylvania/ > Live AQI for 2 Pennsylvania metros, updated hourly from EPA AirNow. Where the state's air is worst right now, and how far apart its cities are. # Pennsylvania air quality today Updated 14 Sep 2026, 22:12 UTC · LIVE 2 metros tracked Across the 2 Pennsylvania metros BreatheCheck measures, air is worst right now in Pittsburgh at AQI 41 (Good) and cleanest in Philadelphia at AQI 36 . ## Which Pennsylvania city has the worst air quality right now? | # | Metro | AQI | UV now | Dominant | | 1 | Pittsburgh | 41 Good | 0.5 | O3 | | 2 | Philadelphia | 36 Good | 0.3 | O3 | ## What is the UV index in Pennsylvania today? The strongest UV in Pennsylvania today is 6 (High) in Pittsburgh, arriving around 1pm local time. The mildest of the 2 metros we model here peaks at 6 in Philadelphia. UV is modelled, not measured — unlike the AQI above it, which comes off an instrument. Hour by hour in Pittsburgh → ## Coke ovens under a valley lid Pennsylvania does not run its air program from one desk. The Department of Environmental Protection’s Bureau of Air Quality covers most of the state, while two jurisdictions operate programs of their own: the Allegheny County Health Department, and Air Management Services inside the Philadelphia Department of Public Health. Which of the three stands behind a given reading depends on where the monitor is. The Allegheny end is where terrain and industry sit on top of each other. The Monongahela runs in a trench cut well below the surrounding plateau, and on cold, calm mornings warmer air settles over the cold air in that trench and caps it. Underneath sit U.S. Steel’s Clairton Coke Works and the rest of the Mon Valley’s coking and steel operations. The stretch of river around Liberty and Clairton carried a fine-particulate nonattainment designation of its own, drawn tighter than the county line, until EPA redesignated it to attainment in July 2025; Allegheny County as a whole remains nonattainment for the 2012 annual PM2.5 standard. Allegheny County wrote a rule requiring large Mon Valley sources to cut emissions during forecast pollution episodes, and EPA incorporated it into Pennsylvania’s state implementation plan in 2024, which ties a control obligation to the weather instead of to an annual permit total. The eastern counties run on different chemistry. Philadelphia and its suburbs sit in a summer ozone problem shared with New Jersey and Delaware, assembled over hours from traffic and refining along a corridor that pays no attention to the state line. A Pittsburgh reading in February and a Bucks County reading in July are two pollutants, two seasons and two regulators, reported on one index. ## Where do these Pennsylvania readings come from? 2 of the 2 metros here report from a named regulatory monitor — Pittsburgh, Philadelphia. The dominant pollutant across Pennsylvania today is O3 . We track 2 metropolitan areas in Pennsylvania, not the whole state, and 2 of them have a page of its own. There is no state-wide average here on purpose: averaging 2 metros into one figure would invent a value for all the ground between them. How we measure, and what we refuse to estimate → ## Neighbouring states Smoke and inversions do not stop at a state line, so when Pennsylvania looks wrong the answer is often next door. ## Related Updated 14 Sep 2026, 22:12 UTC