Air Quality Forecast and Dispersion Outlook for Allegheny County showing that there will be a Strong surface inversion tomorrow, with Moderate overnight.
🚨‼️#Stinkburgh Alert! Strong inversion forecasted for tomorrow morning. Wind from the south. I anticipate that some areas will experience elevated pollution and stench overnight and tomorrow morning. Stay alert. Report smells via ACHD and SmellPGH if you smell something.
Lots of red PurpleAir dots on map of Pittsburgh and Mon Valley showing elevated PM2.5 pollution.
Elevated VOC readings on an Awair monitor for this morning and yesterday morning.
Many, many dark purple SmellPGH reports in Pittsburgh, with several going into the Mon Valley.
ACHD console showing elevated H2S many times in the last several days, including today at the Liberty monitor.
🚨🚨#Stinkburgh Alert‼️🤮 It's just awful outside. Loads of SmellPGH reports. Elevated VOC's, particles, and H2S pollution. The foul sulfur odor woke me up early this morning. Submit complaints to ACHD & SmellPGH app if you smell it. #AirQuality @gasp-pgh.bsky.social @breathe-project.bsky.social
Air Quality Forecast and Dispersion Outlook for Allegheny County, PA on February 9, 2026. Shows forecasted unhealthy air at 104 AQI today, moderate tomorrow at 80 AQI tomorrow, and strong surface inversion expected this morning, tonight, and tomorrow morning. Weak inversion this evening.
And the ACHD dispersion report. Not good.
Image shows H2S levels above the red line of 5ppb today, with some higher spikes in the past few days.
PurpleAir monitor map shows red, purple, orange, and yellow dots, and a few green - but the green are mostly indicated as indoor dots. This shows air pollution is relatively high in the region, particularly the Mon Valley area.
SmellPGH app showing triangles in the Pittsburgh region, more purple in the area around Jefferson Hills, more orange near Pittsburgh. Orange and red pollution monitors in Clairton and Liberty, respectively.
Image shows graph of VOC levels rising into orange today.
‼️#Stinkburgh Alert! ACHD is already reporting a Mon Valley Air Pollution Warning. Particles, VOC’s, and H2S levels are high. Elevated pollution expected into tomorrow, too. Please be careful out there and report smells to the ACHD and SmellPGH if you encounter them.
It was so bad this morning! Thanks to GASP for this write-up! And there is a link lower in the post that explains how to submit an air quality complaint. If you are annoyed by the pollution and/or smell, please submit a complaint to SmellPGH AND the ACHD GovQA system!
Yinz smell that?! That tell-tale stench of rotten eggs? Culprit could be concentrations of Hydrogen sulfide (or H2S for short) that are sky-high in & around the Mon Valley.
But the exceedances don’t tell the whole story. There were also CRAZY HIGH H2S spikes.
www.gasp-pgh.org/smell-that-f...
Hydrogen Sulfide levels graph in Allegheny County, showing high levels for the past 24 hours, higher than nearly all days since September.
Hydrogen Sulfide (H2S) levels have been elevated this AM. And it smells like it STILL at my house. The stench hasn't broken. Weather forecast indicates to my eyes that it might blow out by 1pm today. Until then, I'm holding my nose. @gasp-pgh.bsky.social @breathe-project.bsky.social
SmellPGH app showing red triangles in the Mon Valley area around Pittsburgh, indicating stench reports.
PurpleAir map show with lots of orange red and purple levels in and around the Mon Valley near Pittsburgh.
High VOC levels per an Awair monitor graph.
‼️#Stinkburgh Alert!! 🚨 I woke up around 5am with a headache and the noxious foul odor of sulfur in my bedroom. VOC levels outside were super high overnight. Particles are also up. Just intolerable. I feel violated. #Pittsburgh @breathe-project.bsky.social
Image shows Edgar Thomson Plant engulfed in low lying clouds.
🎼🎶It's beginning to look a lot like a weather inversion. Image shows Edgar Thomson Plant engulfed in low lying clouds. Pollution also gets trapped with the low-lying air. We have inversions often in Pittsburgh, but not usually so visually clear. 🎼🎶
Pittsburgh Region, check this out:
Graph showing spikes in morning and evening. Evening spike goes to purple.
#Stinkburgh Alert ‼️ I haven’t smelled it this bad in a long time. Amazing sulfur and burnt plastic smell. And my Awair VOC sensor is *really* high. 🤮
"Companies were allowed to estimate their chemical pollution using methods that even the EPA conceded were often unreliable.
In 2023, the EPA received irrefutable proof that these estimates were highly flawed." www.propublica.org/article/epa-...
What is this big bright light? This video mostly shows Nippon/US Steel's Edgar Thomson Plant, but I can't tell if the bright light is actually inside the plant grounds. Happened at about 8:53pm on 10/19/2025. (BreatheCam footage via @breathe-project.bsky.social and CMU Create Lab)
PurpleAir graph showing elevated levels of PM2.5 starting around 9am.
SmellPGH app image showing lots of triangles in Pittsburgh today - triangles indicating smell reports.
‼️#Stinkburgh Alert! Walked out my front door a few minutes ago and learned that the "moderate inversion" had yielded awful industrial smells at my house, but not until about 9am. Looks like I'm not the only one reporting. Hopefully clearing out soon, but tomo might also be bad.
#ICYMI: What’s going on at @ussteel.bsky.social’s Edgar Thomson facility? @inversion-doc.bsky.social has flagged myriad emissions events like this one from yesterday:
PurpleAir map showing graph of particles spiking at monitor site between 9am and 9:30am.
Here you can see the spike on the Kennywood Hills B monitor. Anybody in that area encounter this in real-time?
This morning there was a massive plume emitted from Nippon/US Steel's Edgar Thomson Mill in the greater Pittsburgh area. There was a massive spike in particles across the river about that time. The Allegheny County Health Dept needs to investigate. @breathe-project.bsky.social @gasp-pgh.bsky.social
‼️#Stinkburgh Alert! Strong inversion predicted for tomorrow morning in Pittsburgh. Looks like it might get worse over the weekend. Submit #SmellPGH complaints and @HealthAllegheny complaints as you encounter stench! @GASPPgh @BreatheProject @cmucreatelab
It reeeeeaaaalllyyyy stinks like rotten eggs at my house in #Pittsburgh right now. #H2S #Stinkburgh 🏠🤢💩🏭
Map of Pittsburgh with red and orange triangles across much of the eastern end of the city.
PurpleAir nap of air pollution showing elevated levels moving up the Mon Valley int Pittsburgh.
‼️#Stinkburgh Alert! Stench is widely reported across the Pittsburgh region today. VOC and particle levels elevated in certain areas. I decided against my morning walk because of the stench. 💩
Meant to say that "BREATHECAM footage thanks to @BreatheProject and @cmucreatelab." :-)
AirNow.gov monitor graph showing a spike to orange last night in Rankin, PA.
And a monitor a little further away (this was a PurpleAir monitor - not an EPA monitor - but is on the EPA map) shows even higher levels.
AirNow.gov monitor graph showing a spike to orange last night in Braddock, PA.
Even the local EPA regulatory monitor showed a notable spike last night.
PurpleAir graph showing emissions starting to rise a little before 2am, spiking high around 3am and gradually ramping down into the morning.
Here are local PurpleAir monitors near the plant showing significant particle pollution around that time. Winds were very slow.
What in the world happened at Nippon/US Steel's Edgar Thomson facility last night? #AirQuality Footage thanks to @breathe-project.bsky.social and CMU CREATELab. It went on for about 3 HOURS. Local air monitors seem to correlate. @gasp-pgh.bsky.social also reported high H2S last night. 🤬 🧵
HEADS UP: Mon Valley waking up to *another* day of stench and H2S values that exceed the PA 24-hr avg standard.
Smell it? Make reports to ACHD & via SmellPGH. 👀😷
🚨#Stinkburgh Alert! It’s not looking good for stench overnight and into the morning. Plus an ozone alert for the afternoon. Stay careful out there! 😶🌫️
And here is some BreatheCam footage from US Steel's Edgar Thomson Mill between about 8am and 8:30am. Not sure if it has any relation to the smells, but something was emitted from that plant about an hour before the levels spiked. (Footage thx to @breathe-project.bsky.social and CMU CREAT Lab)
Extended spike of VOC's on Awair sensor reading screenshot.
VOC's are still spiking.
Awair sensor reading showing spiking VOC’s
Now VOC’s are spiking:
