Regional secondary PM Possible
Daily PM2.5 peaked at 59 µg/m³ near Cleveland across 2 covered metros home to 2.9 million people. 1 metro 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 ≈ 2.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.0 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
Manual research connected 2 source events to one regional secondary-particle pollution episode using the deterministic grouping rule.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Canada–United States Air Quality Committee · Dec 1, 2004 corroborates
The binational science assessment identifies June 11, 1999 as a summertime PM2.5 episode at Egbert, Ontario. Its exact-date composition profile reports 53.0% sulfate and 23.9% ammonium, with much smaller nitrate, carbon, soil, and other fractions.
U.S. EPA AirData hypothesis
EPA records show median daily PM2.5 of 54.9 micrograms per cubic meter across 3 monitors, 2.652 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (2.164x), sulfur dioxide (2.23x). Other measured comparisons were carbon monoxide (0.96x).
National Weather Service surface observations via Iowa Environmental Mesonet · Jun 11, 1999 hypothesis
Akron recorded calm conditions during 21% of event hours and wind at or below three knots during 29%. Observations included 24 haze hours, minimum visibility 3 miles.
Inference, not direct attribution
exact_date_great_lakes_secondary_composition_fingerprint_possible.v1: This inference is recorded in the catalog methodology.
See every retained source and limitation ↓
Sequence: Cleveland (Jun 11) → Akron (Jun 11)
Evidence path
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.
Source or mechanism
The binational science assessment identifies June 11, 1999 as a summertime PM2.5 episode at Egbert, Ontario. Its exact-date composition profile reports 53.0% sulfate and 23.9% ammonium, with much smaller nitrate, carbon, soil, and other fractions.
View supporting source ↗Air-mass movement
The archived regional study includes June 11, 1999 ozone maps spanning the Upper Midwest and Ohio Valley and explains that elevated pollution initially appeared over industrial source areas in Indiana and Ohio before moving downwind.
View transport source ↗Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 2.7 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓Event autopsy
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.
Cleveland-Elyria, OH
Monitor comparison window 1999-06-08 to 1999-06-14 · PM2.5 target: GT Craig NCore PAMS
77% above nearby days
2 calm hours observed
Haze reported during 23 hours
77% higher than surrounding days
27% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
53% higher than surrounding days
15% higher than surrounding days
12 kt maximum · 2 of 24 observed hours calm
5 observed hours at or below 3 miles
74°F to 92°F
82% maximum
Akron, OH
Monitor comparison window 1999-06-08 to 1999-06-14 · PM2.5 target: East HS
147% above nearby days
5 calm hours observed
Haze reported during 24 hours
147% higher than surrounding days
94% higher than surrounding days
7% lower than surrounding days
118% higher than surrounding days
29% higher than surrounding days
8 kt maximum · 5 of 24 observed hours calm
3 observed hours at or below 3 miles
70°F to 89°F
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.
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.
Views from the selected metro
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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Cleveland-Elyria, OH | 59 µg/m³ | 2.7 | Jun 11, 1999 | #12 of its top days |
| Akron, OH | 56.3 µg/m³ | 2.6 | Jun 11, 1999 | #10 of its top days |
"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
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.
Canada–United States Air Quality Committee
The binational science assessment identifies June 11, 1999 as a summertime PM2.5 episode at Egbert, Ontario. Its exact-date composition profile reports 53.0% sulfate and 23.9% ammonium, with much smaller nitrate, carbon, soil, and other fractions.
A retained source supports the attributed cause for the stated place and dates.
The composition sample is from Egbert, Ontario, not the Cleveland or Akron metro, and the assessment does not prove that each city received the identical air mass.
Canada–United States Air Quality Committee
The binational science assessment identifies June 11, 1999 as a summertime PM2.5 episode at Egbert, Ontario. Its exact-date composition profile reports 53.0% sulfate and 23.9% ammonium, with much smaller nitrate, carbon, soil, and other fractions.
A retained source supports the attributed cause for the stated place and dates.
The composition sample is from Egbert, Ontario, not the Cleveland or Akron metro, and the assessment does not prove that each city received the identical air mass.
City of Chicago study via U.S. EPA archive
The archived regional study includes June 11, 1999 ozone maps spanning the Upper Midwest and Ohio Valley and explains that elevated pollution initially appeared over industrial source areas in Indiana and Ohio before moving downwind.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The maps characterize ozone transport, not Cleveland PM2.5 composition or source-sector shares.
National Weather Service surface observations via Iowa Environmental Mesonet
Akron recorded calm conditions during 21% of event hours and wind at or below three knots during 29%. Observations included 24 haze hours, minimum visibility 3 miles.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
A single surface station documents ventilation and obscuration but not the full vertical profile or particle source mix.
National Weather Service surface observations via Iowa Environmental Mesonet
Cleveland Burke Lakefront recorded calm conditions during 8% of event hours and wind at or below three knots during 13%. Observations included 23 haze hours, minimum visibility 3 miles.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
A single surface station documents weak ventilation and obscuration but not the full vertical profile or particle source mix.
U.S. EPA AirData
EPA records show median daily PM2.5 of 54.9 micrograms per cubic meter across 3 monitors, 2.652 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (2.164x), sulfur dioxide (2.23x). Other measured comparisons were carbon monoxide (0.96x).
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The pollution fingerprint does not uniquely apportion traffic, heating, industry, wood combustion, or secondary aerosol.
U.S. EPA AirData
EPA records show median daily PM2.5 of 58 micrograms per cubic meter across 8 monitors, 2.279 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (1.313x), sulfur dioxide (1.584x). Other measured comparisons were carbon monoxide (0.917x), nitrogen dioxide (1.087x).
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The broad multi-pollutant response does not apportion traffic, heating, industry, wood combustion, or secondary aerosol.
Possible This 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.