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Regional secondary PM Possible

2002-07-06 to 2002-07-07 Kansas City, MO-KS regional secondary-particle pollution episode

July 6, 2002 to July 7, 2002

Daily PM2.5 peaked at 40.7 µg/m³ near Kansas City across 1 covered metro home to 2.3 million people.

Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.1 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

The basis for “Regional secondary PM”

Kansas City, MO-KS's 12-monitor PM2.5 episode reached 38.925 µg/m³, 1.999 times the adjacent-window level, with 17 coded haze hours. 3 exact-date regional chemistry sites agreed that 66.1% to 73.5% of reconstructed mass was ammonium sulfate plus ammonium nitrate, and the largest reconstructed mass was 97.9% of the affected-place PM2.5 value. This supports regional secondary PM at possible confidence; the chemistry sites did not directly sample the city and no particular source region is assigned.

Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.

U.S. EPA AirData Chemical Speciation · Jul 7, 2002 hypothesis

Kansas City, MO-KS regional PM2.5 composition context, 2002-07-07

On the exact event date, 3 EPA speciation sites within 175 km agreed that ammonium sulfate plus ammonium nitrate comprised a majority of reconstructed PM2.5: 20-013-9000 (134.9 km; 71.5% secondary inorganic share; 38.1 µg/m³ reconstructed mass); El Dorado Springs (152.6 km; 66.1% secondary inorganic share; 32.6 µg/m³ reconstructed mass); VIKING LAKE STATE PARK (223.9 km; 73.5% secondary inorganic share; 33.1 µg/m³ reconstructed mass).

Inference, not direct attribution

coherent_nearby_exact_date_secondary_inorganic_context.v1: This inference is recorded in the catalog methodology.

See every retained source and limitation ↓

Evidence path

From source to city

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.

Open the evidence ledger ↓
  1. 1

    Source or mechanism

    Pattern-based explanation

    coherent_nearby_exact_date_secondary_inorganic_context.v1. This inference is recorded in the catalog methodology.

    Inferred
  2. 2

    Air-mass movement

    The 72-hour air-mass history is reconstructed

    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 ↓
    Modeled
  3. 3

    Local response

    40.7 µg/m³ near Kansas City

    EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 1.9 cigarette-equivalents at the outdoor daily rate.

    Inspect the pollutant and weather signals ↓
    Documented

Event autopsy

What the instruments saw

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.

Observed context · not attribution

Kansas City, MO-KS

Monitor comparison window 2002-07-03 to 2002-07-10 · PM2.5 target: JUSTICE CENTER

6 pollutant signals
Fine-particle pulse 38.9 µg/m³

66% above nearby days

Air movement 5 kt median wind

1 calm hour observed

What observers saw 2.5 mi minimum visibility

Haze reported during 17 hours

Pollution fingerprint

Metro-wide median of reporting monitors
PM2.5 38.9 µg/m³

66% higher than surrounding days

Before14.4 µg/m³ Event38.9 µg/m³ After24.5 µg/m³
12 monitors · 24 HOUR
PM10 56 µg/m³

No adjacent-day comparison

Before— Event56 µg/m³ After—
3 monitors · 24 HOUR
Carbon monoxide 0.215 ppm

15% higher than surrounding days

Before0.192 ppm Event0.215 ppm After0.119 ppm
4 monitors · 1 HOUR
Nitrogen dioxide 4.13 ppb

50% lower than surrounding days

Before8.25 ppb Event4.13 ppb After9.77 ppb
6 monitors · 1 HOUR
Sulfur dioxide 0.125 ppb

About the same as surrounding days

Before0.042 ppb Event0.125 ppb After0.146 ppb
4 monitors · 1 HOUR
Ozone 0.059 ppm

34% higher than surrounding days

Before0.034 ppm Event0.059 ppm After0.045 ppm
7 monitors · 8-HR RUN AVG BEGIN HOUR

Atmospheric conditions

OLATHE (OJC), 14.6 km from the PM2.5 target
Wind 5 kt median

13 kt maximum · 1 of 25 observed hours calm

Visibility 2.5 mi minimum

2 observed hours at or below 3 miles

Temperature 81°F median

74°F to 93°F

Humidity 77% median

94% 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

Where the air had been

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.

Transport context · not source attribution

Air arriving near Kansas City

Peak-date arrivals · 2002-07-07

Broad history Mostly east of the metro
72-hour reach 300–750 km
Sensitivity runs 12 modeled paths
Arrival metro
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m

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.

Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond them is unmeasured, not clean: this map shows where IAQng has readings, not the extent of the smoke.
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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.

Affected metros

MetroPeak PM2.5Cigarettes, whole eventPeak dayAll-time standing
Kansas City, MO-KS 40.7 µg/m³ 3.7 Jul 7, 2002 #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

What supports this account

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.

1 retained source

Official record

Kansas City, MO-KS regional PM2.5 composition context, 2002-07-07

U.S. EPA AirData Chemical Speciation

On the exact event date, 3 EPA speciation sites within 175 km agreed that ammonium sulfate plus ammonium nitrate comprised a majority of reconstructed PM2.5: 20-013-9000 (134.9 km; 71.5% secondary inorganic share; 38.1 µg/m³ reconstructed mass); El Dorado Springs (152.6 km; 66.1% secondary inorganic share; 32.6 µg/m³ reconstructed mass); VIKING LAKE STATE PARK (223.9 km; 73.5% secondary inorganic share; 33.1 µg/m³ reconstructed mass).

What it supports

This source supports a possible mechanism or occurrence; it does not establish the cause by itself.

Limit

The chemistry sites were 134.9 km and 152.6 km and 223.9 km from the affected-place PM2.5 target and did not directly measure the city air.

What remains uncertain

Status and provenance

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.