Wildfire smoke EPA monitor flag
Daily PM2.5 peaked at 59 µg/m³ near Boston across 5 covered metros home to 9.4 million people. 3 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 ≈ 2.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 19 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
Supplied qualified evidence supports wildfire-smoke as the root cause. The grouping includes only events linked by explicit shared episode evidence; otherwise this remains a single-event episode.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jul 26, 2021 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 66 PM2.5 samples in the candidate CBSA on 2021-07-26, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jul 26, 2021 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 56 PM2.5 samples in the candidate CBSA on 2021-07-26, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
Connecticut Department of Energy and Environmental Protection · Jul 27, 2021 official
Connecticut DEEP reported that the western-wildfire smoke plume produced unhealthy PM2.5 across Connecticut on July 26, supporting wildfire-smoke attribution for this regional New England event.
See every retained source and limitation ↓
Sequence: Boston (Jul 26) → New Haven (Jul 26) → Hartford (Jul 26) → Worcester (Jul 26) → Providence (Jul 26)
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
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 66 PM2.5 samples in the candidate CBSA on 2021-07-26, identifying wildfire smoke as affecting the samples. An informational qualifier is an official…
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 5 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 “Wildfire smoke” explanation; it does not assign the cause by itself.
Boston-Cambridge-Newton, MA-NH
Monitor comparison window 2021-07-23 to 2021-07-29 · PM2.5 target: ChelmsfordNR
459% above nearby days
About the same as surrounding days
306% higher than surrounding days
459% higher than surrounding days
306% higher than surrounding days
100% higher than surrounding days
21% higher than surrounding days
20% higher than surrounding days
8% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
10% higher than surrounding days
About the same as surrounding days
Hartford-West Hartford-East Hartford, CT
Monitor comparison window 2021-07-23 to 2021-07-29 · PM2.5 target: McAuliffe Park
316% above nearby days
24% lower than surrounding days
232% higher than surrounding days
316% higher than surrounding days
232% higher than surrounding days
19% higher than surrounding days
36% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
7% higher than surrounding days
24% lower than surrounding days
New Haven-Milford, CT
Monitor comparison window 2021-07-23 to 2021-07-29 · PM2.5 target: Criscuolo Park-New Haven
296% above nearby days
38% lower than surrounding days
174% higher than surrounding days
296% higher than surrounding days
174% higher than surrounding days
77% higher than surrounding days
60% higher than surrounding days
About the same as surrounding days
7% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
8% higher than surrounding days
38% lower than surrounding days
Providence-Warwick, RI-MA
Monitor comparison window 2021-07-23 to 2021-07-29 · PM2.5 target: Near Rd
325% above nearby days
10% higher than surrounding days
74% higher than surrounding days
325% higher than surrounding days
74% higher than surrounding days
About the same as surrounding days
11% higher than surrounding days
32% higher than surrounding days
6% lower than surrounding days
About the same as surrounding days
9% higher than surrounding days
10% higher than surrounding days
Worcester, MA-CT
Monitor comparison window 2021-07-23 to 2021-07-29 · PM2.5 target: WORCESTER SUMMER STREET
320% above nearby days
64% higher than surrounding days
320% higher than surrounding days
64% higher than surrounding days
12% higher than surrounding days
18% higher than surrounding days
20% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
9% 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 |
|---|---|---|---|---|
| Boston-Cambridge-Newton, MA-NH | 59 µg/m³ | 2.7 | Jul 26, 2021 | #5 of its top days |
| New Haven-Milford, CT | 50.9 µg/m³ | 2.3 | Jul 26, 2021 | #17 of its top days |
| Hartford-West Hartford-East Hartford, CT | 49.8 µg/m³ | 2.3 | Jul 26, 2021 | #9 of its top days |
| Worcester, MA-CT | 45.3 µg/m³ | 2.1 | Jul 26, 2021 | #9 of its top days |
| Providence-Warwick, RI-MA | 43.7 µg/m³ | 2.0 | Jul 26, 2021 | #18 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.
AQS PM2.5 qualifier IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 66 PM2.5 samples in the candidate CBSA on 2021-07-26, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 56 PM2.5 samples in the candidate CBSA on 2021-07-26, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
Elevated Levels of Fine Particles in Air This Evening Due to Western Wildfires
Connecticut DEEP reported that the western-wildfire smoke plume produced unhealthy PM2.5 across Connecticut on July 26, supporting wildfire-smoke attribution for this regional New England event.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
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.