Regional secondary PM Officially verified
Daily PM2.5 peaked at 59.6 µg/m³ near Baltimore across 2 covered metros home to 9.3 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 ≈ 2.2 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
A published exact-event analysis at the Baltimore Supersite attributes the June 24-25 episode primarily to ammonium sulfate and organic matter.
Officially verified A directly applicable government determination or qualified scientific attribution product identifies this cause.
Aerosol Science and Technology · Aug 1, 2006 corroborates
The exact episode analysis reports PM2.5 rising to 59 micrograms per cubic meter on June 25 and estimates ammonium sulfate plus organic matter comprised 86-98 percent of mass.
See every retained source and limitation ↓
Sequence: Baltimore (Jun 25) → Washington (Jun 25)
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 exact episode analysis reports PM2.5 rising to 59 micrograms per cubic meter on June 25 and estimates ammonium sulfate plus organic matter comprised 86-98 percent of mass.
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 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.
Baltimore-Columbia-Towson, MD
Monitor comparison window 2002-06-22 to 2002-06-28 · PM2.5 target: Oldtown
232% above nearby days
No adjacent-day comparison
232% higher than surrounding days
No adjacent-day comparison
34% higher than surrounding days
22% higher than surrounding days
60% higher than surrounding days
50% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Washington-Arlington-Alexandria, DC-VA-MD-WV
Monitor comparison window 2002-06-22 to 2002-06-28 · PM2.5 target: PG Equestrian Center
232% above nearby days
No adjacent-day comparison
232% higher than surrounding days
No adjacent-day comparison
48% higher than surrounding days
66% higher than surrounding days
229% higher than surrounding days
54% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
7% higher than 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.
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 |
|---|---|---|---|---|
| Baltimore-Columbia-Towson, MD | 59.6 µg/m³ | 2.7 | Jun 25, 2002 | #10 of its top days |
| Washington-Arlington-Alexandria, DC-VA-MD-WV | 58 µg/m³ | 2.6 | Jun 25, 2002 | #15 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.
Aerosol Science and Technology
The exact episode analysis reports PM2.5 rising to 59 micrograms per cubic meter on June 25 and estimates ammonium sulfate plus organic matter comprised 86-98 percent of mass.
A retained source supports the attributed cause for the stated place and dates.
Measurements are centered on Baltimore; Washington applicability comes from the documented shared regional episode.
Officially verified A directly applicable government determination or qualified scientific attribution product identifies this cause.
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.