June 8, 2004 Pittsburgh nighttime-inversion accumulation episode
June 8, 2004
Daily PM2.5 peaked at 71.3 µg/m³ near Pittsburgh across
1 covered metro home to 2.4 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the
average affected resident ≈ 2.6 cigarettes.
Across everyone living in the affected metros, that is the collective equivalent of
≈ 6.3 million cigarettes.
An awareness illustration of outdoor exposure at 22 µg/m³
per cigarette (Berkeley Earth), counting only the event's ranked days; not a
medical dose.
Why we think this happened
The basis for “Other”
Allegheny County Health Department directly reports that a nighttime temperature inversion accumulated very high PM2.5 at Liberty on June 8, 2004. This supports a standalone documented accumulation episode, while the underlying mixture of regional and local anthropogenic emissions remains unidentified.
DocumentedAn agency or publisher page assesses this cause, without an agency record naming the event or an EPA qualifier on the data.
Allegheny County Health Department Air Quality Program · Jun 7, 2005official
ACHD reports that a nighttime temperature inversion accumulated very high PM2.5 and H2S at Liberty on June 8, 2004, under persistent south-southwest winds. This identifies an accumulation mechanism, not the underlying emissions source: the broader study describes a mixture of regional flow and localized urban or anthropogenic excess but does not identify or quantify a single source for this day.
A cause is more convincing when the record connects three things: something happened,
the air mass moved toward the region, and local instruments responded. Here is how much
of that chain is documented for this event.
ACHD reports that a nighttime temperature inversion accumulated very high PM2.5 and H2S at Liberty on June 8, 2004, under persistent south-southwest winds. This identifies an accumulation mechanism, not the underlying emissions source: the broader…
The retained record does not yet show how air traveled from the proposed source to
these metros. A trajectory replay or dated plume analysis belongs here.
Research gap
3
Local response
71.3 µg/m³ near Pittsburgh
EPA monitors recorded the event across 1 metro.
The peak daily concentration is roughly 3.2 cigarette-equivalents at the outdoor daily rate.
Before, during, and after the episode: nearby pollutant monitors and surface-weather
stations show what changed. This context tests the “Other” explanation; it does
not assign the cause by itself.
Observed context · not attribution
Pittsburgh, PA
Monitor comparison window 2004-06-05 to 2004-06-11 · PM2.5 target: Liberty
6 pollutant signals
Fine-particle pulse43.6 µg/m³
73% above nearby days
PM1064 µg/m³
106% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.543.6 µg/m³
73% higher than surrounding days
Before25.2 µg/m³ Event43.6 µg/m³ After11.1 µg/m³
PM1064 µg/m³
106% higher than surrounding days
Before31 µg/m³ Event64 µg/m³ After19 µg/m³
Carbon monoxide0.396 ppm
68% higher than surrounding days
Before0.235 ppm Event0.396 ppm After0.153 ppm
Nitrogen dioxide15.9 ppb
97% higher than surrounding days
Before8.06 ppb Event15.9 ppb After7.79 ppb
Sulfur dioxide7.90 ppb
41% higher than surrounding days
Before5.60 ppb Event7.90 ppb After5.48 ppb
Ozone0.045 ppm
18% higher than surrounding days
Before0.038 ppm Event0.045 ppm After0.017 ppm
Atmospheric conditions
Nearby EPA weather observations
Humidity71 %
About the same as surrounding days
Source: U.S. EPA AirData daily observations and, where available, nearby ASOS/AWOS
surface observations. Values are descriptive medians over the retained monitor set;
missing measurements remain missing. Transport and source evidence remain separate
layers because this instrument pattern does not assign a cause by itself.
Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond
them is unmeasured, not clean: this map shows where IAQng has readings, not the extent
of the smoke.
—
Episode peak
--cigarettes
The smoke map's scale, replayed over this event: the surface interpolates between
covered metros' daily records, framed to the affected region. Hover for a reading,
click a metro to pin it to the card. Days a monitor did not report draw nothing.
Select a metro on the map to see nearby cameras. Where an operator archive reaches
the event, drag the divider to compare two moments, adjust either date and time, or
play the available event-day frames. Camera imagery is visual context, not an
air-quality measurement or proof of smoke.
No useful public camera views are currently available within 80 km of this metro.
"Cigarettes, whole event" totals a metro's ranked event days at 22 µg/m³ per
cigarette: what a person outdoors there breathed across the event, as the
illustration. "All-time standing" is where this episode's days sit in each metro's
ranked record (worst-area measure, since 1999). Full local context is on each
metro's Air Records page.
Public evidence library
What supports this account
Each card states what a source supports—and what it does not. Official records, research, reporting, community observations, and transparent inferences remain visibly different kinds of evidence.
Allegheny County Health Department Air Quality Program · Jason Maranche · Jun 7, 2005officialgovernment
ACHD reports that a nighttime temperature inversion accumulated very high PM2.5 and H2S at Liberty on June 8, 2004, under persistent south-southwest winds. This identifies an accumulation mechanism, not the underlying emissions source: the broader study describes a mixture of regional flow and localized urban or anthropogenic excess but does not identify or quantify a single source for this day.
What remains uncertain
The assessment identifies an atmospheric accumulation mechanism, not a specific underlying emissions source.
The report does not quantify regional versus local anthropogenic source contributions for this day.
Status and provenance
DocumentedAn agency or publisher page assesses this cause, without an agency record naming the event or an EPA qualifier on the data.
This episode was grouped from the monitor record by the catalog pipeline and given
its cause from the evidence listed above. It has not been individually reviewed and
signed off, so its boundaries, cause, and name may change as evidence accumulates.
Grouping policy common_sense_root_cause_grouping.v2. The cause label reflects the
assembled evidence above, not an IAQng detection formula. If it is wrong,
tell us.