Regional secondary PM Possible
Daily PM2.5 peaked at 50.6 µg/m³ near Louisville/Jefferson County across 1 covered metro home to 1.4 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 2.4 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
A peer-reviewed Upper Ohio River Valley study identifies an exact July 13-14, 2000 transported PM2.5 episode whose measured mass at the NETL site was dominated by ammonium sulfate. EPA's later Louisville-specific assessment independently finds that regional sources supply most measured Louisville PM2.5 and that sulfate is the largest warm-season urban-increment component after organic mass. On July 13, Louisville itself recorded a sharp seven-monitor PM2.5 rise, elevated sulfur dioxide and nitrogen dioxide, and persistent haze. Together these observations support regional secondary particles at possible confidence, while the geographic and historical gaps prevent a stronger claim.
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 median daily PM2.5 of 47.65 micrograms per cubic meter across 7 Louisville-area monitors, 2.428 times the adjacent-window level. Sulfur dioxide was 1.446 times and nitrogen dioxide was 1.337 times their adjacent-window comparisons.
National Weather Service surface observations via Iowa Environmental Mesonet · Jul 13, 2000 hypothesis
Louisville International reported haze during 14 event-day hours, visibility at or below three miles during 9 of 24 observed hours, and a minimum visibility of 1.5 miles. Winds were calm during 6 hours and at or below three knots during 8 hours.
Journal of the Air & Waste Management Association · Aug 1, 2004 hypothesis
Anderson and colleagues identify a PM2.5 episode from 12:00 July 13 through 18:00 July 14, 2000 under westerly transport. Their integrated NETL sample reports 24.8 micrograms per cubic meter of ammonium sulfate, versus 0.6 nitrate, 1.4 elemental carbon, 7.5 nonvolatile organic material, and 3.0 semivolatile organic material. The paper links this transport regime to Ohio River Valley emissions and precursor transport.
Inference, not direct attribution
exact_date_regional_sulfate_with_local_haze_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
exact_date_regional_sulfate_with_local_haze_possible.v1. This inference is recorded in the catalog methodology.
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 2.3 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.
Louisville/Jefferson County, KY-IN
Monitor comparison window 2000-07-10 to 2000-07-16 · PM2.5 target: Southwick
96% above nearby days
6 calm hours observed
Haze reported during 14 hours
96% higher than surrounding days
6% higher than surrounding days
56% higher than surrounding days
12% higher than surrounding days
23% higher than surrounding days
9 kt maximum · 6 of 24 observed hours calm
9 observed hours at or below 3 miles
74°F to 88°F
97% 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 Louisville/Jefferson County
Peak-date arrivals · 2000-07-13
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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Louisville/Jefferson County, KY-IN | 50.6 µg/m³ | 2.3 | Jul 13, 2000 | #13 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. Environmental Protection Agency
EPA's Louisville-specific technical assessment finds the average urban increment is less than one-third of total measured PM2.5, indicating a significant regional contribution. Its seasonal component analysis reports that sulfate is Louisville's second-largest urban-increment component and peaks in the third quarter, while concluding that both regional and local sources contribute.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The assessment uses 2011-2013 monitoring and does not analyze July 13, 2000.
National Weather Service surface observations via Iowa Environmental Mesonet
Louisville International reported haze during 14 event-day hours, visibility at or below three miles during 9 of 24 observed hours, and a minimum visibility of 1.5 miles. Winds were calm during 6 hours and at or below three knots during 8 hours.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One airport station cannot establish the regional transport path or vertical mixing profile.
U.S. EPA AirData
EPA records show median daily PM2.5 of 47.65 micrograms per cubic meter across 7 Louisville-area monitors, 2.428 times the adjacent-window level. Sulfur dioxide was 1.446 times and nitrogen dioxide was 1.337 times their adjacent-window comparisons.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The coherent local response supports a real metro episode but does not identify chemical composition or source-sector shares.
Journal of the Air & Waste Management Association
Anderson and colleagues identify a PM2.5 episode from 12:00 July 13 through 18:00 July 14, 2000 under westerly transport. Their integrated NETL sample reports 24.8 micrograms per cubic meter of ammonium sulfate, versus 0.6 nitrate, 1.4 elemental carbon, 7.5 nonvolatile organic material, and 3.0 semivolatile organic material. The paper links this transport regime to Ohio River Valley emissions and precursor transport.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The exact composition sample and trajectories are for the Pittsburgh/Kittanning/Ohio monitoring network, not Louisville.
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.