Why is the air quality bad in Letcher today?

Poor air quality in Letcher is usually driven by one dominant pollutant — most often fine particle pollution (PM2.5) from wildfire smoke, vehicle exhaust, or industry, or ground-level ozone (smog) that builds on hot, sunny, stagnant days. The AQI at the top of this page names which pollutant is highest right now; that pollutant is what's making the air "bad," and weather — heat, calm wind, or smoke blown in from elsewhere — is usually why it spikes on a given day.

Is it safe to exercise outside in Letcher right now?

It depends on the AQI. Below 100 (Good or Moderate) it's generally fine to run or work out outdoors. From 101–150 (Unhealthy for Sensitive Groups), people with asthma, heart conditions, kids, and older adults should shorten or move workouts indoors. At 151+ (Unhealthy) everyone should cut back on hard outdoor exertion, because exercise makes you breathe more polluted air deeper into your lungs. The live verdict at the top of this page gives the go/no-go for Letcher right now.

What AQI level is considered safe?

On the EPA's Air Quality Index, 0–50 (Good, green) is safe for everyone and 51–100 (Moderate, yellow) is acceptable for almost everyone, though unusually sensitive people may notice symptoms. 101–150 (orange) is Unhealthy for Sensitive Groups, 151–200 (red) is Unhealthy for everyone, 201–300 (purple) is Very Unhealthy, and 301+ (maroon) is Hazardous. As a rule of thumb, an AQI under 100 is a safe day for outdoor activity.

What's the main pollutant in Letcher's air?

The two pollutants that most often drive Letcher's AQI are fine particulate matter (PM2.5) and ground-level ozone. PM2.5 tends to dominate in winter, near traffic and industry, and during wildfire smoke events; ozone tends to dominate on hot, sunny summer afternoons. This page identifies the dominant pollutant live — it's the one whose sub-index matches the overall AQI — so you can see which is the problem today rather than guessing by season.

Should I wear a mask at this AQI?

A mask helps most when fine-particle pollution (PM2.5) is high — for example during wildfire smoke. A well-fitted N95 or KN95 filters the fine particles that cause the most harm; cloth and surgical masks do little against them. Most people don't need a mask below an AQI of 150, but at 151+ (Unhealthy) an N95 is worth wearing outdoors, and at 201+ (Very Unhealthy or worse) it's best to stay indoors with air filtration rather than rely on a mask. Note that masks do not filter ground-level ozone.

Letcher, South Dakota Air Quality

Letcher air quality today — the AQI, the main pollutant, and whether it’s safe to exercise outside right now

Letcher, SD · Air quality right now

Is it safe to be outside in Letcher today?

Yes — air quality is Good (AQI 39)

Air is clean — great for outdoor activity.Main pollutant: Ozone

Pollutants right now

PM2.53.0 µg/m³fine particles — smoke, exhaust, soot
PM103.3 µg/m³coarse particles — dust, pollen, ash
Ozone71 µg/m³Main pollutantsmog — builds on hot, sunny days
NO₂3.1 µg/m³nitrogen dioxide — traffic, combustion

ExerciseOK to run — no air-quality limits on outdoor exercise.

How to read Letcher’s air quality

Air quality is reported as the EPA Air Quality Index (AQI), a 0–500 scale that rolls up several pollutants into one number. The six bands run from Good (0–50, green) and Moderate (51–100, yellow) through Unhealthy for Sensitive Groups (101–150, orange), Unhealthy (151–200, red), Very Unhealthy (201–300, purple), and Hazardous (301+, maroon). As a rule of thumb, an AQI under 100 is a safe day for outdoor activity in Letcher; above 100, people with asthma, heart conditions, the very young, and older adults should start to scale back.

The headline AQI is set by whichever pollutant is worst at the moment — usually fine particle pollution (PM2.5) from smoke, traffic, or industry, or ground-level ozone (smog) that builds on hot, sunny, stagnant afternoons. That “dominant” pollutant is what’s making the air bad, and weather is usually why it spikes on a given day: heat and sunlight cook up ozone, calm wind lets pollution pool, and smoke can blow in from fires far away. When a live reading is available it appears at the top of this page with the dominant pollutant named; otherwise this EPA scale is your guide to what any AQI number means.

Frequently asked

Why is the air quality bad in Letcher today?: Poor air quality in Letcher is usually driven by one dominant pollutant — most often fine particle pollution (PM2.5) from wildfire smoke, vehicle exhaust, or industry, or ground-level ozone (smog) that builds on hot, sunny, stagnant days. The AQI at the top of this page names which pollutant is highest right now; that pollutant is what's making the air "bad," and weather — heat, calm wind, or smoke blown in from elsewhere — is usually why it spikes on a given day.
Is it safe to exercise outside in Letcher right now?: It depends on the AQI. Below 100 (Good or Moderate) it's generally fine to run or work out outdoors. From 101–150 (Unhealthy for Sensitive Groups), people with asthma, heart conditions, kids, and older adults should shorten or move workouts indoors. At 151+ (Unhealthy) everyone should cut back on hard outdoor exertion, because exercise makes you breathe more polluted air deeper into your lungs. The live verdict at the top of this page gives the go/no-go for Letcher right now.
What AQI level is considered safe?: On the EPA's Air Quality Index, 0–50 (Good, green) is safe for everyone and 51–100 (Moderate, yellow) is acceptable for almost everyone, though unusually sensitive people may notice symptoms. 101–150 (orange) is Unhealthy for Sensitive Groups, 151–200 (red) is Unhealthy for everyone, 201–300 (purple) is Very Unhealthy, and 301+ (maroon) is Hazardous. As a rule of thumb, an AQI under 100 is a safe day for outdoor activity.
What's the main pollutant in Letcher's air?: The two pollutants that most often drive Letcher's AQI are fine particulate matter (PM2.5) and ground-level ozone. PM2.5 tends to dominate in winter, near traffic and industry, and during wildfire smoke events; ozone tends to dominate on hot, sunny summer afternoons. This page identifies the dominant pollutant live — it's the one whose sub-index matches the overall AQI — so you can see which is the problem today rather than guessing by season.
Should I wear a mask at this AQI?: A mask helps most when fine-particle pollution (PM2.5) is high — for example during wildfire smoke. A well-fitted N95 or KN95 filters the fine particles that cause the most harm; cloth and surgical masks do little against them. Most people don't need a mask below an AQI of 150, but at 151+ (Unhealthy) an N95 is worth wearing outdoors, and at 201+ (Very Unhealthy or worse) it's best to stay indoors with air filtration rather than rely on a mask. Note that masks do not filter ground-level ozone.

More for Letcher

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Pollutants right now

How to read Letcher’s air quality

Frequently asked

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