2001-08-01 to 2001-08-02 Akron, OH, Buffalo-Cheektowaga-Niagara Falls, NY, and 4 other metros regional secondary-particle pollution episode
August 1, 2001 to August 2, 2001
Daily PM2.5 peaked at 57.7 µg/m³ near Akron across
6 covered metros home to 8.1 million people.
4 metros placed a top-ten day in their record.
Counting the extra PM2.5 above each metro's typical day, this event handed the
average affected resident ≈ 2.4 cigarettes.
Across everyone living in the affected metros, that is the collective equivalent of
≈ 20 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 “Regional secondary PM”
Manual research connected 5 source events to one regional secondary-particle pollution episode using the deterministic grouping rule.
PossibleThis is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Journal of the Air & Waste Management Association · May 1, 2005corroborates
SCAMP identifies July 29-August 4 as a regional secondary-PM2.5 episode. Sulfate supplied 47.6% and 46.2% of measured mass on the two composition days, and the authors attribute the episode to secondary formation under warm, sunny, high-pressure stagnation.
Meteorological Service of Canada / American Meteorological Society corroborates
The AURAMS study modeled the July 29-August 4, 2001 episode across eastern Canada and the eastern United States. It reports that August 2 brought high ozone and PM2.5 across Quebec mainly from long-range pollutant transport during hot, humid southwesterly flow; the regional pattern involved high-pressure stagnation followed by southwest transport.
EPA records show median daily PM2.5 of 46.6 micrograms per cubic meter across 4 monitors, 4.591 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were nitrogen dioxide (1.697x), sulfur dioxide (1.697x). Other measured comparisons were carbon monoxide (1.023x).
Inference, not direct attribution
exact_window_regional_secondary_field_study_possible.v1: This inference is recorded in the catalog methodology.
regional_secondary_transboundary_convergence.v1: This inference is recorded in the catalog methodology.
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.
SCAMP identifies July 29-August 4 as a regional secondary-PM2.5 episode. Sulfate supplied 47.6% and 46.2% of measured mass on the two composition days, and the authors attribute the episode to secondary formation under warm, sunny, high-pressure…
Before, during, and after the episode: nearby pollutant monitors and surface-weather
stations show what changed. This context tests the “Regional secondary PM” explanation; it does
not assign the cause by itself.
Observed context · not attribution
Akron, OH
Monitor comparison window 2001-07-30 to 2001-08-05 · PM2.5 target: East HS
5 pollutant signals
Fine-particle pulse56.6 µg/m³
171% above nearby days
PM1064 µg/m³
142% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.556.6 µg/m³
171% higher than surrounding days
Before32.2 µg/m³ Event56.6 µg/m³ After19 µg/m³
PM1064 µg/m³
142% higher than surrounding days
Before40.5 µg/m³ Event64 µg/m³ After23 µg/m³
Carbon monoxide0.733 ppm
About the same as surrounding days
Before0.746 ppm Event0.733 ppm After0.576 ppm
Sulfur dioxide18.3 ppb
165% higher than surrounding days
Before6.93 ppb Event18.3 ppb After5.87 ppb
Ozone0.060 ppm
20% higher than surrounding days
Before0.062 ppm Event0.060 ppm After0.037 ppm
Cincinnati, OH-KY-IN
Monitor comparison window 2001-07-29 to 2001-08-05 · PM2.5 target: Lower Price Hill
Monitor comparison window 2001-07-30 to 2001-08-05 · PM2.5 target: SIMON STREET
5 pollutant signals
Fine-particle pulse46.6 µg/m³
352% above nearby days
Air movement5.86 kt
60% higher than surrounding days
Carbon monoxide0.471 ppm
About the same as surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.546.6 µg/m³
352% higher than surrounding days
Before10 µg/m³ Event46.6 µg/m³ After10.3 µg/m³
Carbon monoxide0.471 ppm
About the same as surrounding days
Before0.387 ppm Event0.471 ppm After0.533 ppm
Nitrogen dioxide21.7 ppb
69% higher than surrounding days
Before12.8 ppb Event21.7 ppb After12.8 ppb
Sulfur dioxide11.7 ppb
67% higher than surrounding days
Before7 ppb Event11.7 ppb After6.75 ppb
Ozone0.074 ppm
73% higher than surrounding days
Before0.043 ppm Event0.074 ppm After0.032 ppm
Atmospheric conditions
Nearby EPA weather observations
Humidity73.5 %
8% higher than surrounding days
Pressure999 Millibars
About the same as surrounding days
Temperature79.1 °F
About the same as surrounding days
Wind5.86 kt
60% higher than surrounding days
Syracuse, NY
Monitor comparison window 2001-07-30 to 2001-08-05 · PM2.5 target: DEC REGIONAL OFFICE
4 pollutant signals
Fine-particle pulse44.5 µg/m³
460% above nearby days
Air movement4 kt median wind
6 calm hours observed
What observers saw3 mi minimum visibility
Haze reported during 15 hours
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.544.5 µg/m³
460% higher than surrounding days
Before7.95 µg/m³ Event44.5 µg/m³ After7.70 µg/m³
Carbon monoxide0.550 ppm
About the same as surrounding days
Before0.604 ppm Event0.550 ppm After0.575 ppm
Sulfur dioxide5.38 ppb
316% higher than surrounding days
Before1.19 ppb Event5.38 ppb After1.29 ppb
Ozone0.061 ppm
90% higher than surrounding days
Before0.032 ppm Event0.061 ppm After0.028 ppm
Atmospheric conditions
SYRACUSE/HANCOCK, 8.5 km from the PM2.5 target
Wind4 kt median
11 kt maximum · 6 of 24 observed hours calm
Visibility3 mi minimum
2 observed hours at or below 3 miles
Temperature79.5°F median
65°F to 91°F
Humidity75% median
90% maximum
Rochester, NY
Monitor comparison window 2001-07-30 to 2001-08-05
4 pollutant signals
Fine-particle pulse42 µg/m³
367% above nearby days
Air movement8 kt median wind
15 kt maximum
What observers saw5 mi minimum visibility
Haze reported during 12 hours
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.542 µg/m³
367% higher than surrounding days
Before8.60 µg/m³ Event42 µg/m³ After9 µg/m³
Carbon monoxide0.421 ppm
13% lower than surrounding days
Before0.440 ppm Event0.421 ppm After0.536 ppm
Sulfur dioxide7.02 ppb
144% higher than surrounding days
Before1.81 ppb Event7.02 ppb After4.46 ppb
Ozone0.070 ppm
99% higher than surrounding days
Before0.035 ppm Event0.070 ppm After0.035 ppm
Atmospheric conditions
ROCHESTER/MONROE CO, 7.7 km from the PM2.5 target
Wind8 kt median
15 kt maximum · No calm observed hours
Visibility5 mi minimum
0 observed hours at or below 3 miles
Temperature79.5°F median
68°F to 89°F
Humidity69% median
81% maximum
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.
Air-mass reconstruction
Where the air had been
NOAA HYSPLIT traces the air arriving at each metro backward for 72 hours. Multiple
arrival times and heights show whether the broad path is stable—or sensitive to
assumptions about when and where the polluted layer arrived.
Transport context · not source attribution
Air arriving near Cincinnati
Peak-date arrivals · 2001-08-02
Broad historyMostly south of the metro
72-hour reach100–500 km
Sensitivity runs12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
Each line begins 72 hours before arrival and points toward the metro. Color represents
arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions.
A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near Columbus
Peak-date arrivals · 2001-08-02
Broad historyMostly south of the metro
72-hour reach100–500 km
Sensitivity runs12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
Each line begins 72 hours before arrival and points toward the metro. Color represents
arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions.
A path can show where the air traveled, but it cannot prove which source added the PM2.5.
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.
14 retained sources
Official record
Buffalo-Cheektowaga-Niagara Falls, NY surface conditions, 2001-08-02
National Weather Service surface observations via Iowa Environmental Mesonet
BUFFALO INTL ARPT recorded calm conditions during 0% of event hours and wind at or below three knots during 0%. Observations included 20 haze hours, minimum visibility 4 miles.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
A single surface station documents ventilation and obscuration but not the full vertical profile or particle source mix.
Official record
Syracuse, NY surface conditions, August 2, 2001
National Weather Service surface observations via Iowa Environmental Mesonet
SYRACUSE/HANCOCK recorded 15 haze-coded hours, median visibility of 5.5 miles, median wind of 4 knots, and median sea-level pressure of 1020.55 millibars on August 2.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
One airport station documents the local air mass and obscuration but not particle composition or the full metropolitan mixing layer.
Official record
Rochester, NY surface conditions, August 2, 2001
National Weather Service surface observations via Iowa Environmental Mesonet
ROCHESTER/MONROE CO recorded 12 haze-coded hours, median visibility of 6.5 miles, median wind of 8 knots, and median sea-level pressure of 1020.8 millibars on August 2.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
One airport station documents the local air mass and obscuration but not particle composition or the full metropolitan mixing layer.
Official record
Buffalo-Cheektowaga-Niagara Falls, NY joint pollution fingerprint, 2001-08-02
U.S. EPA AirData
EPA records show median daily PM2.5 of 46.6 micrograms per cubic meter across 4 monitors, 4.591 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were nitrogen dioxide (1.697x), sulfur dioxide (1.697x). Other measured comparisons were carbon monoxide (1.023x).
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The pollution fingerprint does not uniquely apportion traffic, heating, industry, wood combustion, or secondary aerosol.
Official record
Syracuse, NY joint pollution fingerprint, August 2, 2001
U.S. EPA AirData
EPA records show median daily PM2.5 of 44.5 micrograms per cubic meter across 3 monitors, compared with 7.95 in the adjacent-window comparison. Eight-hour ozone rose to 0.0611 ppm and sulfur dioxide rose to 5.375 ppb.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The pollution fingerprint demonstrates a simultaneous multi-pollutant episode but cannot by itself distinguish transported secondary aerosol from local emissions.
Official record
Rochester, NY joint pollution fingerprint, August 2, 2001
U.S. EPA AirData
EPA records show median daily PM2.5 of 42 micrograms per cubic meter across 2 monitors, compared with 9 in the adjacent-window comparison. Eight-hour ozone rose to 0.0703 ppm and sulfur dioxide rose to 7.0208 ppb.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The pollution fingerprint demonstrates a simultaneous multi-pollutant episode but cannot by itself distinguish transported secondary aerosol from local emissions.
Scientific research
The Steubenville Comprehensive Air Monitoring Program (SCAMP): Analysis of Short-Term and Episodic Variations in PM2.5 Concentrations Using Hourly Air Monitoring Data
Journal of the Air & Waste Management Association
SCAMP identifies July 29-August 4 as a regional secondary-PM2.5 episode. Sulfate supplied 47.6% and 46.2% of measured mass on the two composition days, and the authors attribute the episode to secondary formation under warm, sunny, high-pressure stagnation.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The intensive monitor was in Steubenville; applying the regional episode to Cincinnati and Columbus is capped at possible.
Scientific research
The Steubenville Comprehensive Air Monitoring Program (SCAMP): Analysis of Short-Term and Episodic Variations in PM2.5 Concentrations Using Hourly Air Monitoring Data
Journal of the Air & Waste Management Association
SCAMP identifies July 29-August 4 as a regional secondary-PM2.5 episode. Sulfate supplied 47.6% and 46.2% of measured mass on the two composition days, and the authors attribute the episode to secondary formation under warm, sunny, high-pressure stagnation.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The intensive composition monitor was in Steubenville; applicability to Akron and Buffalo is regional and capped at possible.
Show 6 more retained sources
Scientific research
The Steubenville Comprehensive Air Monitoring Program (SCAMP): Analysis of Short-Term and Episodic Variations in PM2.5 Concentrations Using Hourly Air Monitoring Data
Journal of the Air & Waste Management Association
SCAMP identifies July 29-August 4, 2001 as a regional secondary-PM2.5 episode. Sulfate supplied 47.6% and 46.2% of measured mass on the two composition days, and the authors describe secondary formation under warm, sunny, high-pressure conditions; the highest concentrations occurred overnight August 1-2 under reduced mixing heights.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The composition measurements were made in Steubenville, Ohio, not at the New York metro; they establish the same-window regional episode and mechanism but not a city-specific source fraction.
Scientific research
The Steubenville Comprehensive Air Monitoring Program (SCAMP): Analysis of Short-Term and Episodic Variations in PM2.5 Concentrations Using Hourly Air Monitoring Data
Journal of the Air & Waste Management Association
SCAMP identifies July 29-August 4 as a regional secondary-PM2.5 episode. Sulfate supplied 47.6% and 46.2% of measured mass on the two composition days, and the authors attribute the episode to secondary formation under warm, sunny, high-pressure stagnation.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The intensive composition monitor was in Steubenville; applicability to Akron and Buffalo is regional and capped at possible.
Scientific research
The Steubenville Comprehensive Air Monitoring Program (SCAMP): Analysis of Short-Term and Episodic Variations in PM2.5 Concentrations Using Hourly Air Monitoring Data
Journal of the Air & Waste Management Association
SCAMP identifies July 29-August 4, 2001 as a regional secondary-PM2.5 episode. Sulfate supplied 47.6% and 46.2% of measured mass on the two composition days, and the authors describe secondary formation under warm, sunny, high-pressure conditions; the highest concentrations occurred overnight August 1-2 under reduced mixing heights.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The composition measurements were made in Steubenville, Ohio, not at the New York metro; they establish the same-window regional episode and mechanism but not a city-specific source fraction.
Scientific research
Atmospheric Emission Reduction Scenarios Simulated by Canadian AURAMS Model
Meteorological Service of Canada / American Meteorological Society
The AURAMS study modeled the July 29-August 4, 2001 episode across eastern Canada and the eastern United States. It reports that August 2 brought high ozone and PM2.5 across Quebec mainly from long-range pollutant transport during hot, humid southwesterly flow; the regional pattern involved high-pressure stagnation followed by southwest transport.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The paper validates the episode at Quebec sites and does not directly apportion PM2.5 at Buffalo, Rochester, or Syracuse.
Scientific research
Atmospheric Emission Reduction Scenarios Simulated by Canadian AURAMS Model
Meteorological Service of Canada / American Meteorological Society
The AURAMS study modeled the July 29-August 4, 2001 episode across eastern Canada and the eastern United States. It reports that August 2 brought high ozone and PM2.5 across Quebec mainly from long-range pollutant transport during hot, humid southwesterly flow; the regional pattern involved high-pressure stagnation followed by southwest transport.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The paper validates the episode at Quebec sites and does not directly apportion PM2.5 at Buffalo, Rochester, or Syracuse.
Scientific research
Atmospheric Emission Reduction Scenarios Simulated by Canadian AURAMS Model
Meteorological Service of Canada / American Meteorological Society
The AURAMS study modeled the July 29-August 4, 2001 episode across eastern Canada and the eastern United States. It reports that August 2 brought high ozone and PM2.5 across Quebec mainly from long-range pollutant transport during hot, humid southwesterly flow; the regional pattern involved high-pressure stagnation followed by southwest transport.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The paper validates the episode at Quebec sites and does not directly apportion PM2.5 at Buffalo, Rochester, or Syracuse.
What remains uncertain
Akron and Buffalo remain separate place-scoped estimates projected onto audited local episodes.
The field study supports a regional mechanism but does not provide city-specific source apportionment for Cincinnati or Columbus.
The possible classification identifies a regional secondary-particle mechanism, not one emitting facility or a quantified origin share.
The regional studies support a secondary-particle and transport mechanism but do not assign city-specific source fractions.
The two scientific studies describe the same regional episode at Steubenville and Quebec sites rather than directly measuring New York source fractions.
Status and provenance
PossibleThis is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
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.