Regional secondary PM Possible
Daily PM2.5 peaked at 49.4 µg/m³ near Virginia Beach across 1 covered metro home to 1.8 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.9 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 3.4 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
MARAMA identifies July 18-19 as a severe, widespread PM episode under regional stagnation and separately attributes the episode's sharp particle increase to transported ammonium sulfate associated with coal combustion. A Baltimore Supersite analysis independently describes the same dates as a sulfate-and-organic-matter regional haze episode. The evidence supports a possible regional secondary-PM mechanism for coastal Virginia, while no Norfolk-area source fraction is available.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
MARAMA / Maryland Department of the Environment · Sep 30, 2004 official
MARAMA characterizes July 18-19, 2002 as a severe PM-conducive episode across its mid-Atlantic domain under a broad ridge, a Georgia-centered surface high, stagnant winds, heat, and haze. Its episode analysis says nearly all of the measured increase at the Essex speciation site was ammonium sulfate and links the westerly transport to coal-combustion sulfate.
Aerosol Science and Technology · Aug 1, 2006 corroborates
The Baltimore Supersite study treats July 18-19 as a regional haze episode and reports that ammonium sulfate plus organic matter accounted for roughly 90 to 96 percent of episode-average PM2.5 in the studied regional haze cases.
Inference, not direct attribution
official_regional_sulfate_episode_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
MARAMA characterizes July 18-19, 2002 as a severe PM-conducive episode across its mid-Atlantic domain under a broad ridge, a Georgia-centered surface high, stagnant winds, heat, and haze. Its episode analysis says nearly all of the measured increase…
View supporting source ↗Air-mass movement
NOAA HYSPLIT modeled 12 backward paths across multiple arrival times and heights. They show where the air traveled, not which source polluted it.
Explore the modeled paths ↓Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.2 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.
Virginia Beach-Norfolk-Newport News, VA-NC
Monitor comparison window 2002-07-15 to 2002-07-21 · PM2.5 target: MONITORS ON GROUND IN FENCED COMPOUND AT O.F. SMITH STADIUM
78% above nearby days
16 kt maximum
Haze reported during 17 hours
78% higher than surrounding days
14% lower than surrounding days
36% higher than surrounding days
101% higher than surrounding days
31% higher than surrounding days
16 kt maximum · No calm observed hours
0 observed hours at or below 3 miles
75°F to 95°F
85% 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.
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 Virginia Beach-Norfolk-Newport News
Peak-date arrivals · 2002-07-18
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 |
|---|---|---|---|---|
| Virginia Beach-Norfolk-Newport News, VA-NC | 49.4 µg/m³ | 2.2 | Jul 18, 2002 | #14 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 characterizes July 18-19, 2002 as a severe PM-conducive episode across its mid-Atlantic domain under a broad ridge, a Georgia-centered surface high, stagnant winds, heat, and haze. Its episode analysis says nearly all of the measured increase at the Essex speciation site was ammonium sulfate and links the westerly transport to coal-combustion sulfate.
An official source supports the attributed cause for the stated place and dates.
The detailed composition site was in Maryland, not the Virginia Beach metro.
MARAMA / Maryland Department of the Environment
MARAMA's dated PM2.5 assessment includes the 2002-07-18 episode and provides the regional meteorological classification needed for targeted follow-up.
Context for the event; this item does not establish the attributed cause by itself.
The accessible passage does not establish a sufficiently specific event-wide emitting source or mechanism for every grouped metro.
Aerosol Science and Technology
The Baltimore Supersite study treats July 18-19 as a regional haze episode and reports that ammonium sulfate plus organic matter accounted for roughly 90 to 96 percent of episode-average PM2.5 in the studied regional haze cases.
A retained source supports the attributed cause for the stated place and dates.
The measurements were made in Baltimore and cannot be treated as a Virginia Beach source-apportionment result.
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.