Temperature inversion Possible
Daily PM2.5 peaked at 45.5 µg/m³ near Jackson across 1 covered metro home to 606,178 people. 1 metro placed a top-ten day in their record.
Why we think this happened
Jackson, MS's 3-monitor PM2.5 value was 2.189 times the adjacent-window comparison. Surface observations recorded wind at or below three knots during 75% of event-day hours, and a nearby event-date radiosonde measured a surface-based inversion of 3.4 degrees Celsius through 330 meters above ground. Together, these observations support temperature-inversion accumulation as a possible mechanism. They do not identify the trapped particle sources.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service surface observations via Iowa Environmental Mesonet · Aug 7, 1999 hypothesis
JACKSON/THOMPSON recorded calm conditions during 46% of event hours and wind at or below three knots during 75%. Observations included 23 haze hours, minimum visibility 3 miles.
U.S. EPA AirData hypothesis
EPA records show median daily PM2.5 of 45.1 micrograms per cubic meter across 3 monitors, 2.189 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (1.432x), carbon monoxide (1.286x). Other measured comparisons were sulfur dioxide (1x).
NOAA/NWS radiosonde observations via Iowa Environmental Mesonet · Aug 7, 1999 hypothesis
Jackson Area -- KHKS KJAN's 12 UTC radiosonde profile measured temperature rising 3.4 degrees Celsius from 91 to 421 meters, a 330-meter surface-based inversion. The NOAA/IGRA station is 6.9 kilometers from the PM2.5 target monitor.
Inference, not direct attribution
exact_radiosonde_inversion_plus_multimonitor_accumulation_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_radiosonde_inversion_plus_multimonitor_accumulation_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 2.1 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 “Temperature inversion” explanation; it does not assign the cause by itself.
Jackson, MS
Monitor comparison window 1999-08-04 to 1999-08-10 · PM2.5 target: RANKIN CO HEALTH DEPARTMENT-ROOF
58% above nearby days
11 calm hours observed
Haze reported during 23 hours
58% higher than surrounding days
33% higher than surrounding days
35% higher than surrounding days
8% higher than surrounding days
14% higher than surrounding days
6 kt maximum · 11 of 24 observed hours calm
2 observed hours at or below 3 miles
76°F to 98°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.
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 |
|---|---|---|---|---|
| Jackson, MS | 45.5 µg/m³ | 2.1 | Aug 7, 1999 | #3 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.
National Weather Service surface observations via Iowa Environmental Mesonet
JACKSON/THOMPSON recorded calm conditions during 46% of event hours and wind at or below three knots during 75%. Observations included 23 haze hours, minimum visibility 3 miles.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
A single surface station documents weak ventilation and obscuration but not the full vertical profile or particle source mix.
NOAA/NWS radiosonde observations via Iowa Environmental Mesonet
Jackson Area -- KHKS KJAN's 12 UTC radiosonde profile measured temperature rising 3.4 degrees Celsius from 91 to 421 meters, a 330-meter surface-based inversion. The NOAA/IGRA station is 6.9 kilometers from the PM2.5 target monitor.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The radiosonde station is 6.9 kilometers from the PM2.5 target monitor and may not represent every part of the metro airshed.
U.S. EPA AirData
EPA records show median daily PM2.5 of 45.1 micrograms per cubic meter across 3 monitors, 2.189 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (1.432x), carbon monoxide (1.286x). Other measured comparisons were sulfur dioxide (1x).
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The broad multi-pollutant response does not apportion traffic, heating, industry, wood combustion, or secondary aerosol.
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.