Regional secondary PM Possible
Daily PM2.5 peaked at 44.9 µg/m³ near Charlotte across 1 covered metro 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 ≈ 1.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 4.4 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
Exact-date NWS and surface observations document a stagnant, hazy, nearly calm Charlotte air mass while regulatory monitors show a broad, continuing PM2.5 episode that fell sharply after the pattern changed. EPA's North Carolina assessment identifies sulfate-dominated regional haze as the usual summertime fine-particle mechanism under stagnant, humid, low-wind conditions. Together these support regional secondary PM as a possible mechanism, not an exact-day source apportionment.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. EPA AirData hypothesis
EPA records show daily PM2.5 near 42 micrograms per cubic meter across five federal-reference monitors and 43.6 across two additional monitoring series during a continuing episode; the comparison medians fell to roughly 11 and 7 micrograms per cubic meter afterward.
National Weather Service Greenville-Spartanburg via Iowa Environmental Mesonet hypothesis
The exact-date NWS discussion called the pattern stagnant and anticipated reduced visibility from mist and haze around its terminal forecast sites.
National Weather Service surface observations via Iowa Environmental Mesonet hypothesis
Charlotte's official surface station recorded 14 calm hours, 16 hours at or below three knots, 12 hours of haze, and 12 hours of mist on August 5.
Inference, not direct attribution
multi_monitor_fingerprint_with_local_seasonal_profile_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
multi_monitor_fingerprint_with_local_seasonal_profile_possible.v1. This inference is recorded in the catalog methodology.
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 2.0 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.
Charlotte-Concord-Gastonia, NC-SC
Monitor comparison window 2005-08-02 to 2005-08-08
29% above nearby days
32% lower than surrounding days
15% higher than surrounding days
29% higher than surrounding days
15% higher than surrounding days
About the same as surrounding days
48% lower than surrounding days
8% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
32% lower 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 |
|---|---|---|---|---|
| Charlotte-Concord-Gastonia, NC-SC | 44.9 µg/m³ | 2.0 | Aug 5, 2005 | #9 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.
U.S. EPA AirData
EPA records show daily PM2.5 near 42 micrograms per cubic meter across five federal-reference monitors and 43.6 across two additional monitoring series during a continuing episode; the comparison medians fell to roughly 11 and 7 micrograms per cubic meter afterward.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The monitor response establishes a broad particle episode but does not determine its chemical composition or exclude transported smoke.
National Weather Service Greenville-Spartanburg via Iowa Environmental Mesonet
The exact-date NWS discussion called the pattern stagnant and anticipated reduced visibility from mist and haze around its terminal forecast sites.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion documents the atmospheric setting but does not attribute Charlotte's measured PM2.5 to a chemical component or source sector.
National Weather Service surface observations via Iowa Environmental Mesonet
Charlotte's official surface station recorded 14 calm hours, 16 hours at or below three knots, 12 hours of haze, and 12 hours of mist on August 5.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Surface haze supports the episode setting but does not identify the aerosol's source or composition.
U.S. Environmental Protection Agency and North Carolina Division of Air Quality
The official North Carolina assessment says sulfate is the largest contributor to regional haze and that peak southeastern hazy days occur in summer under stagnant weather, high relative humidity, high temperatures, and low wind speeds.
Context for the event; this item does not establish the attributed cause by itself.
The assessment describes the state's recurring seasonal mechanism; it does not provide exact-day chemical measurements for August 5, 2005.
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.