<UPDATED> More H2S Exceedances, Poor Air Quality On Tap for Mon Valley Today

Updated: Oct 26

UPDATE #3: As expected, concentrations of PM2.5 exceeded federal health-based standards at Allegheny County Health Department's air quality monitor in Liberty Borough.


UPDATE #2: The Allegheny County Health Department issued the following Allegheny Alert at 6:24 a.m. today, Oct. 26.


The Mon Valley Episode Warning, which lasted from October 22-26, has ended. Overall atmospheric conditions have improved in the Mon Valley, and are expected to continue to do so moving forward. The Air Quality Index in the area is now below the threshold level for particulate matter (PM2.5).


UPDATE #1: The Allegheny County Health Department issued the following Allegheny Alert at 5:24 p.m. today, Oct. 25:


Based on the Pennsylvania Department of Environmental Protection's forecast, the Mon Valley Air Pollution Warning will continue through at least tomorrow morning, October 26. The ACHD's Air Quality Program is monitoring the situation and will reassess conditions tomorrow. Staff will provide future updates to residents, as new information becomes available.


Mon Valley residents awoke Tuesday to the stench of sulfur and rotten eggs, soaring concentrations of fine particulate matter, and a Code Orange Air Quality Action Day alert from the state Department of Environmental Protection, meaning levels of fine particulate matter (PM2.5) are expected to exceed the federal health-based standard today.


To put the stench into perspective, concentrations of hydrogen sulfide (or H2S) were so high this morning at Allegheny County Health Department’s air quality monitor in Liberty Borough that another exceedance of Pennsylvania’s 24-hour standard was guaranteed - the second day in a row for such an exceedance and the 16th so far this month.

A quick word about H2S: It’s a colorless gas recognizable by its rotten egg odor and the concentrations we see in the Mon Valley can cause irritation to the eyes, nose, or throat as well as headaches, poor memory, tiredness, and balance problems. It may also cause difficulty in breathing for some asthmatics, according to the Agency for Toxic Substances and Disease Registry.

Levels of fine particulate matter at the Liberty monitor were even more concerning: During the 7 a.m. hour, PM2.5 soared to 137 ug/m3 - the highest reading so far this month, and October has been a pretty rough month. While the concentration dipped slightly since then, a Mon Valley Air Pollution Warning remains in place.


In an Allegheny Alert issued Tuesday morning, Allegheny County Health Department officials said a reprieve from this latest bout of poor air quality may come as soon as tonight:


The Mon Valley Episode Rule warning is still in effect. Very light winds and a strong inversion will contribute to code ORANGE levels of PM2.5 in the Liberty-Clairton area with the highest concentrations coming between now and 11 a.m. Air quality is expected to improve this afternoon and evening as the inversion breaks.

GASP continues to follow this issue closely and will keep you updated. In the meantime, we graphed the H2S and PM2.5 concentrations for those who'd like to take a deeper dive into the data:






204 views0 comments