Past Few Days Have Seen Mixed Bag of Air Quality & Confusion - More of the Same Expected Today

This past weekend in southwestern Pennsylvania was idyllic: There were unseasonably warm temperatures, peak fall color, and plentiful sunshine. But for those in the Mon Valley (and downwind of it), the past few days were marred – at times – by unhealthy air quality, malodors, and a still-in-place Mon Valley Air Pollution Warning.


Considering the public received many messages concerning air quality over the past few days – some from the Allegheny County Health Department (ACHD) and some courtesy of sources outside ACHD’s control (namely, Apple Inc. and state Department of Environmental Protection (DEP) air quality monitors) – we figured a recap was in order:


FRIDAY: Some Poor Air Quality and a Lot of Confusion


Mon Valley residents woke up Friday to high concentrations of fine particulate matter (known as PM2.5), the pollutant normally driving air quality to hit “unhealthy” levels. EPA’s NowCast AQI values were well in excess of 100 based on PM2.5 concentrations reported at ACHD’s air quality monitor in Liberty Borough. This means PM2.5 concentrations were in the orange, unhealthy-for-sensitive populations range.


Around the same time, Apple’s (and iPhone’s) preferred air quality forecasting company – Breezometer – added a great deal of confusion to the situation. Starting Thursday afternoon, readings of coarse particulate matter (known as PM10) from DEP’s Beaver Falls air quality monitor started to show outrageously high values.


While the DEP data page has since deleted the data – a sure sign the values were due to a monitor error – GASP staff noted a reading of 957 ug/m3 Thursday afternoon and a later reading of -63 ug/m3, suggesting to us that yes, the monitor was likely misbehaving.


DEP later confirmed in media reports that this was, in fact, the case.


Those erroneous values appear to have been published through Friday morning. While the EPA’s NowCast AQI was not factoring the Beaver Falls data into its calculations, Breezometer was. The result of this Apple-only issue was that while some local residents were suffering through poor air quality Friday, some others erroneously were seeing ‘middle-of-a-wildfire’ or ‘something-has-clearly-exploded’ types of AQI values.


To its credit, ACHD responded, but somewhat inaccurately, which might have made the situation worse, or at least more confusing. An Allegheny Alert sent out Friday morning around 11:30 a.m. stated:


This morning, multiple air quality/weather apps reported “unhealthy for sensitive groups” levels of particulate matter (PM2.5). Many apps try to predict what PM2.5 levels will be as the day goes on. When the levels are increasing, the apps show a higher PM2.5 level for the rest of the day. When there is a weather inversion, the apps over predict PM2.5 levels until late morning. Allegheny County monitors measure air quality hourly. They do not predict readings. Currently, and throughout the morning, our monitors have measured “good” to “moderate” air quality levels for PM2.5, SO2 and ozone. Members of the Air Quality Program will continue to monitor the situation.


The core problem with this message was that it appeared to commingle the actual issue of high levels of PM2.5 at its Liberty monitor and the imaginary issue of high PM10 broadcast via Apple. In fact, EPA’s NowCast AQI was correctly showing “unhealthy for sensitive groups” values on Friday morning. It appears to us that Breezometer was incorrectly showing purple “very unhealthy” AQI values exceeding 200 for portions of Allegheny County.


The result was that ACHD seemed to be downplaying actual poor air quality that ended up culminating with an exceedance of the federal health-based standard for PM2.5 at ACHD’s air quality monitor in Liberty Borough (based on official but preliminary data).


Still with us? Good - let’s proceed with the rest of the weekend.


SATURDAY: More Poor Air Quality But Somewhat of a Reprieve


Just like Friday morning, Mon Valley residents woke up to high concentrations of PM2.5. Unlike Friday morning, ACHD outreach was clearer.


PM2.5 levels coupled with predicted continued poor atmospheric conditions prompted ACHD early Saturday to issue a Mon Valley Air Pollution Warning. It stated:


An Air Pollution Warning has been issued for the Mon Valley for the remainder of today and all of tomorrow. The 24-hour PM2.5 standard for the Mon Valley has been exceeded at an official monitoring station in the Mon Valley and is likely to continue.


Young children, the elderly, and those with respiratory problems, such as asthma, emphysema, and bronchitis, are especially vulnerable to the effects of air pollution and should limit outdoor activities during this time.


Companies most significantly contributing to particulate pollution in the Mon Valley region are required to temporarily reduce particulate emissions.


In addition, the DEP that day declared Sunday would be a Code Orange Air Quality Action Day for fine particulate matter in the Liberty-Clairton area of Allegheny County.


These predictions left GASP staff and likely others following these developments worried about just how bad air quality might get.


As it turned out, while atmospheric forecasting looked bleak, hard monitor data wasn’t as terrifying. It was suboptimal for sure, but Saturday ended without any exceedances of the PM2.5 standard.


SUNDAY: Where Did the Pollution Go?


While PM2.5 values waxed and waned across ACHD’s air quality monitoring network, continued poor dispersion spurred the department at 4 p.m. Sunday to issue an updated message through Allegheny County’s public alert system:


The Mon Valley Air Pollution Warning will continue through at least tomorrow morning, October 24. The ACHD’s Air Quality Program is monitoring the situation and will reassess conditions tomorrow after the weather inversion breaks. Staff will provide future updates to residents, as new information becomes available.


Young children, the elderly, and those with respiratory problems, such as asthma, emphysema, and bronchitis, are especially vulnerable to the effects of air pollution and should limit outdoor activities during this time.


But like Saturday, Sunday ended without any of ACHD’s air quality monitor site showing PM2.5 levels that exceeded the federal standard. What happened?


There are three related issues we hope ACHD and the public will consider when assessing these past few days:


  1. The average wind direction at Liberty from 1 p.m. Thursday through 1 p.m. Saturday was 195 degrees (south-southwest, which is the wind direction that blows emissions from U.S. Steel’s Clairton Coke facility directly toward ACHD’s Liberty monitor). Since then (1 p.m. Saturday through 1 p.m. today), the average wind direction was 91 degrees (due east). Translation: While atmospheric dispersion has been very poor the past two days, what little wind we’ve had could have pushed Mon Valley emissions away from ACHD monitors.

  2. It’s not clear if the wind, the Mon Valley Air Pollution Mitigation Plan actions, both, or neither affected PM2.5 levels these past few days. Given that there have only been a few Mon Valley Air Pollution Warnings declared since the regulation was adopted, we hope ACHD and industry will examine and share findings about these instances.

  3. In light of the past days’ forecasts predicting prolonged and exceptionally poor atmospheric dispersion, we applaud ACHD for keeping the Warning in place through at least Tuesday morning given the threat that has existed to public health.


GASP also wants to remind folks that ACHD monitors do not cover every square inch of Allegheny County - ACHD acting to protect all residents and residents actively reporting issues are both imperative. That said, we encourage residents who have been impacted by poor air quality to make reports to ACHD every time. As a reminder, here’s the link to submit them online.


TODAY: Ugly Forecast, Waiting to See


While ACHD monitor data show levels of fine particulate matter subsided Sunday into Monday, today’s forecast of continued poor air dispersion means concentrations of PM2.5 and other pollutants could again surge before they subside.


As we mentioned, the Mon Valley Air Pollution Warning has been extended through Tuesday morning.


GASP staff continues to follow this issue and will keep you posted. In the meantime, we graphed the air quality data for those who’d like to take a deeper dive:




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