Regional secondary PM Likely
Daily PM2.5 peaked at 69.6 µg/m³ near Pittsburgh across 14 covered metros home to 22 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 ≈ 2.6 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 57 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 5 source events to one regional secondary-particle pollution episode using the deterministic grouping rule.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
MARAMA / Maryland Department of the Environment · Sep 30, 2004 official
MARAMA describes August 13, 2002 as a widespread event from Richmond to Philadelphia under an upper-level ridge, light winds, surface high pressure, heat, haze, and fog, and concludes most summer events reflect regional PM buildup and transport.
NESCAUM official
NESCAUM documents August 11-16, 2002 as a severe Northeast regional transport/stagnation episode with elevated PM2.5 and other secondary pollutants.
Northeast States for Coordinated Air Use Management official
Documents a significant Northeast regional transport/stagnation event from August 11–16, 2002, with elevated PM2.5 and other secondary pollutants; includes Pittsburgh and regional monitoring and trajectory material.
See every retained source and limitation ↓
Sequence: Pittsburgh (Aug 11) → Cleveland (Aug 11) → Springfield (Aug 12) → Scranton (Aug 12) → Buffalo (Aug 12) → Rochester (Aug 12) → Albany (Aug 12) → Syracuse (Aug 12) → Worcester (Aug 13) → Baltimore (Aug 13) → +4 more metros
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
NESCAUM documents August 11-16, 2002 as a severe Northeast regional transport/stagnation episode with elevated PM2.5 and other secondary pollutants.
View supporting source ↗Air-mass movement
Documents a significant Northeast regional transport/stagnation event from August 11–16, 2002, with elevated PM2.5 and other secondary pollutants; includes Pittsburgh and regional monitoring and trajectory material.
View transport source ↗Local response
EPA monitors recorded the event across 14 metros. The peak daily concentration is roughly 3.2 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 2002-08-08 to 2002-08-15 · PM2.5 target: St Theodosius
64% above nearby days
13% higher than surrounding days
64% higher than surrounding days
13% higher than surrounding days
22% higher than surrounding days
14% higher than surrounding days
16% higher than surrounding days
29% higher than surrounding days
Pittsburgh, PA
Monitor comparison window 2002-08-08 to 2002-08-15 · PM2.5 target: Liberty
47% above nearby days
70% higher than surrounding days
47% higher than surrounding days
70% higher than surrounding days
14% higher than surrounding days
About the same as surrounding days
18% higher than surrounding days
18% higher than surrounding days
Buffalo-Cheektowaga-Niagara Falls, NY
Monitor comparison window 2002-08-08 to 2002-08-15 · PM2.5 target: BUFFALO
75% above nearby days
About the same as surrounding days
No adjacent-day comparison
75% higher than surrounding days
No adjacent-day comparison
About the same as surrounding days
21% higher than surrounding days
37% higher than surrounding days
10% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Springfield, MA
Monitor comparison window 2002-08-09 to 2002-08-17 · PM2.5 target: LIBERTY ST PARKING LOT
139% above nearby days
No adjacent-day comparison
139% higher than surrounding days
No adjacent-day comparison
About the same as surrounding days
8% higher than surrounding days
64% higher than surrounding days
43% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Boston-Cambridge-Newton, MA-NH
Monitor comparison window 2002-08-09 to 2002-08-17 · PM2.5 target: NORTH END SITE CENTRAL ARTERY
163% above nearby days
No adjacent-day comparison
163% higher than surrounding days
No adjacent-day comparison
69% higher than surrounding days
45% higher than surrounding days
41% higher than surrounding days
28% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Hartford-West Hartford-East Hartford, CT
Monitor comparison window 2002-08-09 to 2002-08-17 · PM2.5 target: McAuliffe Park
101% above nearby days
No adjacent-day comparison
101% higher than surrounding days
No adjacent-day comparison
10% higher than surrounding days
48% higher than surrounding days
42% lower than surrounding days
25% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Providence-Warwick, RI-MA
Monitor comparison window 2002-08-09 to 2002-08-17 · PM2.5 target: FRANCIS SCHOOL East Providence
130% above nearby days
No adjacent-day comparison
130% higher than surrounding days
No adjacent-day comparison
16% higher than surrounding days
15% higher than surrounding days
125% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Worcester, MA-CT
Monitor comparison window 2002-08-09 to 2002-08-17
143% above nearby days
No adjacent-day comparison
143% higher than surrounding days
No adjacent-day comparison
20% higher than surrounding days
29% higher than surrounding days
30% higher than surrounding days
30% higher than surrounding days
About the same as surrounding days
Albany-Schenectady-Troy, NY
Monitor comparison window 2002-08-09 to 2002-08-16 · PM2.5 target: SCHENECTADY
37% above nearby days
49% lower than surrounding days
30% higher than surrounding days
37% higher than surrounding days
30% higher than surrounding days
9% higher than surrounding days
17% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
49% lower than surrounding days
Rochester, NY
Monitor comparison window 2002-08-09 to 2002-08-16
75% above nearby days
About the same as surrounding days
7% higher than surrounding days
75% higher than surrounding days
7% higher than surrounding days
31% higher than surrounding days
17% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Scranton--Wilkes-Barre--Hazleton, PA
Monitor comparison window 2002-08-09 to 2002-08-16 · PM2.5 target: Scranton
76% above nearby days
74% higher than surrounding days
76% higher than surrounding days
74% higher than surrounding days
95% higher than surrounding days
50% higher than surrounding days
82% higher than surrounding days
12% higher than surrounding days
Syracuse, NY
Monitor comparison window 2002-08-09 to 2002-08-16 · PM2.5 target: EAST SYRACUSE
11% above nearby days
9% lower than surrounding days
About the same as surrounding days
11% higher than surrounding days
About the same as surrounding days
15% lower than surrounding days
7% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
9% lower than surrounding days
Baltimore-Columbia-Towson, MD
Monitor comparison window 2002-08-10 to 2002-08-16 · PM2.5 target: Oldtown
173% above nearby days
61% higher than surrounding days
173% higher than surrounding days
61% higher than surrounding days
46% higher than surrounding days
345% higher than surrounding days
31% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Richmond, VA
Monitor comparison window 2002-08-10 to 2002-08-16
153% above nearby days
15% higher than surrounding days
153% higher than surrounding days
15% higher than surrounding days
13% higher than surrounding days
About the same as surrounding days
25% higher than surrounding days
About the same as surrounding days
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.
Air-mass reconstruction
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.
Air arriving near Buffalo-Cheektowaga-Niagara Falls
Peak-date arrivals · 2002-08-12
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 Cleveland-Elyria
Peak-date arrivals · 2002-08-11
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 Pittsburgh
Peak-date arrivals · 2002-08-11
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 Albany-Schenectady-Troy
Peak-date arrivals · 2002-08-12
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 Rochester
Peak-date arrivals · 2002-08-12
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 Scranton--Wilkes-Barre--Hazleton
Peak-date arrivals · 2002-08-12
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 Syracuse
Peak-date arrivals · 2002-08-12
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 Boston-Cambridge-Newton
Peak-date arrivals · 2002-08-13
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 Hartford-West Hartford-East Hartford
Peak-date arrivals · 2002-08-13
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 Providence-Warwick
Peak-date arrivals · 2002-08-13
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 Springfield
Peak-date arrivals · 2002-08-12
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 Worcester
Peak-date arrivals · 2002-08-13
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 Baltimore-Columbia-Towson
Peak-date arrivals · 2002-08-13
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 Richmond
Peak-date arrivals · 2002-08-13
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.
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 |
|---|---|---|---|---|
| Pittsburgh, PA | 69.6 µg/m³ | 3.2 | Aug 11, 2002 | #24 of its top days |
| Springfield, MA | 57.4 µg/m³ | 7.2 | Aug 12, 2002 | #7 of its top days |
| Cleveland-Elyria, OH | 57.3 µg/m³ | 2.6 | Aug 11, 2002 | #17 of its top days |
| Worcester, MA-CT | 56.2 µg/m³ | 4.6 | Aug 13, 2002 | #2 of its top days |
| Scranton--Wilkes-Barre--Hazleton, PA | 54.2 µg/m³ | 4.6 | Aug 12, 2002 | #12 of its top days |
| Baltimore-Columbia-Towson, MD | 52.7 µg/m³ | 2.4 | Aug 13, 2002 | #17 of its top days |
| Hartford-West Hartford-East Hartford, CT | 52 µg/m³ | 2.4 | Aug 13, 2002 | #7 of its top days |
| Boston-Cambridge-Newton, MA-NH | 51.2 µg/m³ | 4.6 | Aug 13, 2002 | #10 of its top days |
| Buffalo-Cheektowaga-Niagara Falls, NY | 43.1 µg/m³ | 2.0 | Aug 12, 2002 | #19 of its top days |
| Rochester, NY | 42.4 µg/m³ | 1.9 | Aug 12, 2002 | #13 of its top days |
| Richmond, VA | 42.2 µg/m³ | 1.9 | Aug 13, 2002 | #15 of its top days |
| Albany-Schenectady-Troy, NY | 42.1 µg/m³ | 1.9 | Aug 12, 2002 | #21 of its top days |
| Providence-Warwick, RI-MA | 41.2 µg/m³ | 1.9 | Aug 13, 2002 | #22 of its top days |
| Syracuse, NY | 39.8 µg/m³ | 3.5 | Aug 12, 2002 | #16 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.
MARAMA / Maryland Department of the Environment
MARAMA describes August 13, 2002 as a widespread event from Richmond to Philadelphia under an upper-level ridge, light winds, surface high pressure, heat, haze, and fog, and concludes most summer events reflect regional PM buildup and transport.
An official source supports the attributed cause for the stated place and dates.
The mechanism is regional and does not identify a single source.
NESCAUM
NESCAUM documents August 11-16, 2002 as a severe Northeast regional transport/stagnation episode with elevated PM2.5 and other secondary pollutants.
An official source supports the attributed cause for the stated place and dates.
The assessment describes the regional episode and does not apportion every metro separately.
NESCAUM
NESCAUM directly characterizes the event dates as a major regional transport and stagnation episode with elevated secondary pollutants.
An official source supports the attributed cause for the stated place and dates.
NESCAUM
The assessment defines August 11-16, 2002 as a Northeast regional transport and stagnation episode with elevated PM2.5 and secondary pollutants.
An official source supports the attributed cause for the stated place and dates.
NESCAUM
NESCAUM independently identifies August 11-16 as a regional transport/stagnation episode producing elevated PM2.5 and secondary pollutants.
An official source supports the attributed cause for the stated place and dates.
NESCAUM's core documentation is centered farther north.
NESCAUM
NESCAUM documents August 11-16, 2002 as a severe Northeast regional transport/stagnation episode with elevated PM2.5 and other secondary pollutants.
An official source supports the attributed cause for the stated place and dates.
The assessment describes the regional episode and does not apportion every metro separately.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
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.