Pollution Analyst
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National rankings · 2024

Most & Least Polluted Counties

One ranking per pollution indicator. Each table reads the same federal corpus the rest of this site is built on — TRI for chemical releases, EPA AQS for PM2.5, AirToxScreen for hazardous-air cancer risk, and GHGRP for greenhouse gases. Spans 50 ingested states (3146 counties total).

Top 10 most polluted counties

PM2.5 Annual Mean (µg/m³)What is PM2.5?Fine inhalable particles 2.5 micrometers or smaller — about 1/30th the width of a human hair. They travel deep into the lungs and into the bloodstream, and are linked to asthma, heart disease, stroke, and premature death.

Counties with the highest annual PM2.5 concentrations measured at EPA AQS monitors.

Methodology →

Counties ranked by pm2.5 annual mean (µg/m³), highest first.
#CountyStatePopulationPM2.5 Annual Mean
1Power CountyIdaho7,91822.854
2Escambia CountyAlabama36,75516.850
3Cabarrus CountyNorth Carolina226,39616.672
4Kenton CountyKentucky169,06616.242
5Cameron CountyTexas421,85415.608
6Lowndes CountyMississippi58,54715.536
7Trinity CountyCalifornia15,88915.517
8Greenwood CountySouth Carolina69,30915.509
9Mississippi CountyArkansas40,36115.465
10Harney CountyOregon7,49615.460
Top 10 least polluted counties

PM2.5 Annual Mean (µg/m³)What is PM2.5?Fine inhalable particles 2.5 micrometers or smaller — about 1/30th the width of a human hair. They travel deep into the lungs and into the bloodstream, and are linked to asthma, heart disease, stroke, and premature death.

Counties with the lowest annual PM2.5 concentrations measured at EPA AQS monitors.

Methodology →

Counties ranked by pm2.5 annual mean (µg/m³), lowest first.
#CountyStatePopulationPM2.5 Annual Mean
1Park CountyColorado17,5971.673
2Denali BoroughAlaska2,1011.765
3Hughes CountySouth Dakota17,8122.203
4Kauai CountyHawaii73,5112.292
5Hawaii CountyHawaii202,1632.407
6Albany CountyWyoming37,5252.453
7Potter CountyTexas117,9052.470
8Carbon CountyWyoming14,6092.567
9Washakie CountyWyoming7,7252.636
10Jerome CountyIdaho24,4742.667
Top 10 most polluted counties

Lifetime Cancer Risk (All Pollutants) (per million)What this meansEPA-modeled added cancer cases per million residents from a lifetime of breathing local air toxics (AirToxScreen). EPA flags 100-in-a-million as elevated.

Counties with the highest AirToxScreen-modeled lifetime cancer risk from local air toxics.

Methodology →

Counties ranked by lifetime cancer risk (all pollutants) (per million), highest first.
#CountyStatePopulationLifetime Cancer Risk (All Pollutants)
1St. John the Baptist ParishLouisiana41,98678.9
2Clackamas CountyOregon420,92577.3
3Santa Cruz CountyCalifornia268,57170.0
4Butte CountyCalifornia213,60554.8
5Ascension ParishLouisiana126,97353.9
6Multnomah CountyOregon808,09851.9
7Cape Girardeau CountyMissouri81,70350.8
8Iberville ParishLouisiana30,21049.5
9Sacramento CountyCalifornia1,579,21149.0
10Placer CountyCalifornia406,60848.1
Top 10 least polluted counties

Lifetime Cancer Risk (All Pollutants) (per million)What this meansEPA-modeled added cancer cases per million residents from a lifetime of breathing local air toxics (AirToxScreen). EPA flags 100-in-a-million as elevated.

Counties with the lowest AirToxScreen-modeled lifetime cancer risk from local air toxics.

Methodology →

Counties ranked by lifetime cancer risk (all pollutants) (per million), lowest first.
#CountyStatePopulationLifetime Cancer Risk (All Pollutants)
1Aleutians East BoroughAlaska3,4077.2
2Aleutians West Census AreaAlaska5,2197.4
3Nome Census AreaAlaska10,0187.4
4Kusilvak Census AreaAlaska8,3727.8
5Skagway MunicipalityAlaska1,3038.0
6North Slope BoroughAlaska10,9248.1
7Northwest Arctic BoroughAlaska7,6828.5
8Bethel Census AreaAlaska18,5388.9
9Lake and Peninsula BoroughAlaska9999.0
10Haines BoroughAlaska2,0799.1
Top 10 most polluted counties

TRI Air Releases (lb)What this meansToxic chemicals reported by industrial facilities as released to the air — fugitive leaks plus smokestack emissions. Higher pounds means more inhaled exposure for nearby residents. Self-reported under EPA's Toxics Release Inventory.

Counties whose industrial facilities reported the largest air releases under TRI.

Methodology →

Counties ranked by tri air releases (lb), highest first.
#CountyStatePopulationTRI Air Releases
1Mercer CountyNorth Dakota8,36619.0M lb
2Ascension ParishLouisiana126,97312.4M lb
3Harris CountyTexas4,726,17710.9M lb
4Lake CountyIndiana497,6828.0M lb
5Iberville ParishLouisiana30,2107.4M lb
6St. Charles ParishLouisiana52,1917.3M lb
7Columbia CountyOregon52,8656.4M lb
8Jefferson CountyTexas254,9426.2M lb
9Garfield CountyOklahoma62,4566.1M lb
10Rockdale CountyGeorgia93,6415.5M lb
Top 10 least polluted counties

TRI Air Releases (lb)What this meansToxic chemicals reported by industrial facilities as released to the air — fugitive leaks plus smokestack emissions. Higher pounds means more inhaled exposure for nearby residents. Self-reported under EPA's Toxics Release Inventory.

Counties with the smallest reported TRI air releases among those with reporting facilities.

Methodology →

Among counties with reported activity · counties with zero tri air releasesare excluded so the ranking isn't filled with places that simply host no facilities.

Counties ranked by tri air releases (lb), lowest first.
#CountyStatePopulationTRI Air Releases
1North Slope BoroughAlaska10,9241 lb
2Santa Cruz CountyArizona47,8381 lb
3Eagle CountyColorado55,6501 lb
4Glades CountyFlorida12,1791 lb
5Indian River CountyFlorida160,9861 lb
6Paulding CountyGeorgia169,8981 lb
7Union CountyGeorgia24,8801 lb
8McDonough CountyIllinois27,3701 lb
9Barber CountyKansas4,0811 lb
10Martin CountyKentucky11,2981 lb
Top 10 most polluted counties

Greenhouse Gases (GHGRP) (metric tons CO₂e)What this meansGreenhouse gases reported by large industrial emitters under EPA's Greenhouse Gas Reporting Program, in metric tons of CO₂ equivalent. Drives climate warming and the heat-related health effects that follow.

Counties hosting the largest GHGRP-reporting industrial emitters.

Methodology →

Counties ranked by greenhouse gases (ghgrp) (metric tons CO₂e), highest first.
#CountyStatePopulationGreenhouse Gases (GHGRP)
1Harris CountyTexas4,726,177431.6M mtCO₂e
2Chambers CountyTexas47,037302.2M mtCO₂e
3Jefferson CountyTexas254,942270.0M mtCO₂e
4Bexar CountyTexas2,014,059252.8M mtCO₂e
5Los Angeles CountyCalifornia9,936,690203.2M mtCO₂e
6Nueces CountyTexas353,245154.5M mtCO₂e
7Calcasieu ParishLouisiana210,770131.8M mtCO₂e
8Lake CountyIndiana497,682112.3M mtCO₂e
9Galveston CountyTexas350,801110.0M mtCO₂e
10St. John the Baptist ParishLouisiana41,98699.0M mtCO₂e