Regional secondary PM Possible
Daily PM2.5 peaked at 57.4 µg/m³ near Akron across 1 covered metro home to 702,209 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 ≈ 3.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 2.6 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
Akron recorded a coherent three-monitor PM2.5 episode with 40 haze hours and weak surface flow. An exact-date regional assessment identifies July 18 as a high-PM2.5 Pittsburgh Air Quality Study day, and the peer-reviewed July 2001 source-apportionment study found that most secondary material was transported ammonium sulfate arriving from the west and southwest. The transfer to Akron is therefore only possible, not a metro-specific source allocation.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Cabada et al., Journal of the Air & Waste Management Association · Oct 1, 2007 corroborates
The peer-reviewed July 2001 analysis attributed 49% of fine-particle mass to transported secondary material dominated by ammonium sulfate from the west and southwest, plus another 24% to secondary aerosol formed through midday photochemistry.
Mid-Atlantic Regional Air Management Association corroborates
The regional guide uses July 18, 2001 as a high-PM2.5 Pittsburgh Air Quality Study day and explains that stagnant warm high-pressure periods produced the highest concentrations, while sulfate, nitrate, and organic carbon patterns indicated strong regional transport and meteorological control.
National Weather Service surface observations via Iowa Environmental Mesonet · Jul 18, 2001 hypothesis
Akron recorded calm conditions during 46% of event hours and wind at or below three knots during 60%. Observations included 40 haze hours, minimum visibility 0.75 miles.
Inference, not direct attribution
exact_window_regional_study_overlap_possible.v1: This inference is recorded in the catalog methodology.
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 peer-reviewed July 2001 analysis attributed 49% of fine-particle mass to transported secondary material dominated by ammonium sulfate from the west and southwest, plus another 24% to secondary aerosol formed through midday photochemistry.
View supporting source ↗Air-mass movement
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.
Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.6 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.
Akron, OH
Monitor comparison window 2001-07-15 to 2001-07-22 · PM2.5 target: East HS
47% above nearby days
22 calm hours observed
Haze reported during 40 hours
47% higher than surrounding days
33% higher than surrounding days
About the same as surrounding days
10% lower than surrounding days
13% higher than surrounding days
6 kt maximum · 22 of 48 observed hours calm
22 observed hours at or below 3 miles
66°F to 85°F
82% 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 |
|---|---|---|---|---|
| Akron, OH | 57.4 µg/m³ | 4.7 | Jul 19, 2001 | #7 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.
Mid-Atlantic Regional Air Management Association
The regional guide identifies July 18, 2001 as a high-PM2.5 field-study day in Pittsburgh and explains that sulfate and organic aerosol there have large regional contributions. Northeast Ohio's official trend report separately lists ozone exceedances on July 18 and 19.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Pittsburgh and Northeast Ohio context supports a regional pollution episode but does not chemically apportion Akron's PM2.5.
National Weather Service surface observations via Iowa Environmental Mesonet
Akron recorded calm conditions during 46% of event hours and wind at or below three knots during 60%. Observations included 40 haze hours, minimum visibility 0.75 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.
Mid-Atlantic Regional Air Management Association
The regional guide uses July 18, 2001 as a high-PM2.5 Pittsburgh Air Quality Study day and explains that stagnant warm high-pressure periods produced the highest concentrations, while sulfate, nitrate, and organic carbon patterns indicated strong regional transport and meteorological control.
A retained source supports the attributed cause for the stated place and dates.
The documented site is Pittsburgh, not Akron; the evidence is transferred only as a possible regional mechanism across a same-window northeastern Ohio/western Pennsylvania episode.
U.S. EPA AirData
EPA records show median daily PM2.5 of 50.75 micrograms per cubic meter across 3 monitors, 1.933 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (1.633x), carbon monoxide (1.269x). Other measured comparisons were sulfur dioxide (0.793x).
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.
Cabada et al., Journal of the Air & Waste Management Association
The peer-reviewed July 2001 analysis attributed 49% of fine-particle mass to transported secondary material dominated by ammonium sulfate from the west and southwest, plus another 24% to secondary aerosol formed through midday photochemistry.
A retained source supports the attributed cause for the stated place and dates.
The study apportions the Pittsburgh intensive, not the Akron monitors; it supports a regional-secondary interpretation but cannot quantify Akron's event-specific fractions.
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.