When air quality in your area reaches unhealthy levels, we'll send you a quick alert, along with expert tips on how to reduce your exposure.
The Air Quality Index (AQI) measures how polluted the air is and how it may affect your health.
0–50 (Good): Air quality is satisfactory.
51–100 (Moderate): Acceptable, but some pollutants may pose minor concerns.
101–150 (Unhealthy for Sensitive Groups)
151–200 (Unhealthy)
201–300 (Very Unhealthy)
301+ (Hazardous)
Still okay for most, but if you have asthma or allergies, take it easy and avoid long outdoor workouts.
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The live AQI map on this page shows Winston-Salem's current air quality, drawn from EPA-monitored stations and refreshed through the day. Readings below 50 are Good, and above 100 sensitive groups should ease off outdoors. Ozone drives the warm-season swings in Forsyth County, fine particulate the cold-season and smoke-day spikes. Whatever the map reads outside, your filter decides what you breathe indoors.
Forsyth County writes the Winston-Salem forecast, not Raleigh. The nine Triad counties belong to the Forsyth County Office of Environmental Assistance and Protection.
Three county monitors sit behind it: Hattie Avenue, Clemmons Middle School and Union Cross.
Ozone is forecast from March through October and fine particulate all year.
Canadian smoke put the Triad under a Code Red Air Quality Action Day on June 7, 2023.
EPA recommends MERV 13 during smoke events, or the highest rating your system takes.
Start with the map above. The color tells you what to do before the number does, and the pollutant it names matters too, because ozone and fine particulate call for opposite responses indoors. The U.S. AQI runs 0 to 500 across six categories, Good through Hazardous.
EPA AirNow guidance.
EPA AirNow guidance.
It smells like smoke outside and the dial still says yellow. The sensor is fine. EPA reports AQI as a NowCast, an average of up to 12 previous hours, so during a passing plume the number trails your eyes and nose. How the AQI is calculated explains why. Trust what you see, then check the AirNow Fire and Smoke Map.
It depends on the reading. Below 50 the air is fine for everyone, and from 51 to 100 for most. Above 100, people with asthma, COPD or heart disease, plus children and adults over 65, should ease off outdoors, and above 150 so should everyone. With a diagnosed condition, follow the plan your doctor gave you.
Winston-Salem's next-day forecast is not written in Raleigh. NC DAQ covers every county except the nine Triad counties, where the Forsyth County Office of Environmental Assistance and Protection issues the daily code. That office has run local air programs since 1968.
Read it on the Forsyth County forecast page or the N.C. Air Quality Portal, and free EnviroFlash emails send the next-day code for your ZIP.
Winston-Salem air quality varies by ZIP code. Blocks near Salem Parkway, U.S. 52 and I-40 carry more traffic particulate and nitrogen dioxide than those toward Clemmons. Compare counties on the Filterbuy North Carolina air quality map, or the Greensboro AQI map when smoke tracks east.
Forsyth County EAP network.
Forsyth County EAP network.
Six pollutants feed the AQI, and whichever scores highest sets the number. Here that is almost always ozone or fine particulate.
Ozone is the warm-season problem. Ground-level ozone forms when sunlight cooks vehicle and industrial emissions, and it peaks on hot, stagnant afternoons. The federal eight-hour ozone standard is 0.070 ppm, and the Triad sat in nonattainment for years before attaining the 1997 standard on 2005 to 2007 data.
Fine particulate is the year-round problem. PM2.5 particles run about a thirtieth the width of a human hair, and the local sources are traffic, wood smoke, regional power generation such as Duke Energy's Belews Creek Steam Station in Stokes County, and distant fires.
The difference matters indoors. Ozone breaks down quickly once it is inside, so closing the windows handles most of it. Fine particulate will not cooperate, drifting in around doors and windows and hanging for hours. Removing it takes filtration, which is where your MERV rating stops being a spec-sheet detail.
Pollen is not among the six pollutants the AQI covers, so Winston-Salem can post a green reading on a morning your car is yellow. Forsyth County fills that gap itself. A Rotorod sampler downtown runs weekday mornings and staff count the grains under a microscope for a pollen report published by 3:30 p.m., with separate tree, grass and weed ratings and a three-day forecast. Cedar starts in mid-February, oak peaks in April, and ragweed runs into mid-September.
Wildfire smoke is a Winston-Salem variable now, even when the fires burn a thousand miles away. On June 7, 2023 Canadian smoke put North Carolina under a Code Red or Code Orange Air Quality Action Day, the Code Red covering the Triad. Closer to home, the Winston Weaver fertilizer plant fire of January 31, 2022 forced roughly 6,500 residents out.
Follow AirNow and Forsyth County guidance first. Filterbuy does not make portable purifiers, and a portable HEPA unit alongside whole-home filtration is right. MERV 13 versus HEPA for smoke explains the split. Track plumes on our live North Carolina wildfire and smoke map and follow CDC guidance on wildfire smoke.
Filterbuy treats 100 as the line to act on. EPA's category boundary sits at 101, so 100 is still the top of Moderate, and we would rather move at the line than after it. EPA recommends a filter rated MERV 13 or higher in a central system during smoke events. Acting on it at 100 is our call, not EPA's.
Put MERV 13 in the HVAC if the system runs a lower tier. It moves far more air than any portable unit.
Set the thermostat fan to On. Auto filters only while the system runs.
Run a portable HEPA air cleaner in each occupied room, bedrooms first.
Close the house up, and do not add indoor smoke: no candles, no frying, no vacuuming without a sealed unit.
During smoke, check the filter rather than counting days and replace it once it looks dark brown or black, well before the normal interval. Keep spares on hand. A Code Orange day in Forsyth County also bans open burning until the alert lifts.
If your home runs on radiators, window units or ductless mini splits, there is no filter slot and every MERV recommendation here is useless to you. Portable HEPA is your primary defense rather than a supplement, and Filterbuy would rather say so than sell a filter that fits nothing.
Buy a portable HEPA air cleaner sized by EPA's clean-room rule, a smoke CADR at least two thirds of the room's square footage. A 300 square foot bedroom wants about 200.
Keep windows shut and set a window unit to recirculate, but never seal into a hot house without cooling, which EPA warns is dangerous.
Most air quality pages stop at the outdoor number. Filterbuy has built pleated filters in the United States since 2013, and our side of the problem starts where the map ends. Three things stand out.
1. The local program is unusually good and unusually underused. Ninety-one of the state's hundred counties are forecast out of Raleigh. Forsyth is not one of them.
2. A smoke day is an ambush in a way an ozone day is not. Ozone is forecast a day ahead because it needs heat and sunlight, while smoke lifts the index within hours. Every smoke page Filterbuy publishes carries the same advice. Order ahead of the season.
Two readings of 160 can mean completely different weeks. One built over a hot Piedmont afternoon and breaks with the next front. The other rode in on the wind and can sit for days. Winston-Salem gets more of the second kind now, and the filter doing the work that afternoon is the one that was already in the furnace that morning.
Michelle Wan, Brand Manager and Air Quality Writer, Filterbuy
This is the part Filterbuy makes, so here is how we choose. EPA recommends MERV 13 during smoke events, or the highest your system supports, and it is what we run in our own homes. Shop MERV 8, MERV 11, MERV 13 or the Odor Eliminator carbon filter.
Confirm the filter size the way you would for any replacement.
Confirm the filter size the way you would for any replacement.
EPA notes that most furnaces and HVAC systems accommodate MERV 13 without equipment problems, provided the filter is replaced often.
1. Asthma ER visits rose 17 percent on wildfire smoke days.
19 smoke days nationwide, April 30 to August 4, 2023.
A smoke day meant PM2.5 at AQI 101 or higher.
HHS Region 4, covering North Carolina, logged excess visits.
Source: CDC, Morbidity and Mortality Weekly Report, August 2023
2. MERV 13 to 16 cuts indoor particles by up to 95 percent.
Fan on On, not Auto: up to 24 percent.
Portable high-efficiency cleaner: up to 85 percent.
Source: EPA, Wildfire Smoke Factsheet: Indoor Air Filtration (EPA-452/F-18-005)
3. Four in ten Americans breathe air graded F.
Nearly 33 million fail all three measures.
Graded on ozone and two particle measures, 2022 to 2024.
Use the live AQI map at the top of this page, which draws from EPA-monitored stations and colors each reading to the six official categories. Winston-Salem air quality shifts hour by hour, so check it rather than an earlier number.
Match the live map to its category. Below AQI 50 the air is good for everyone. Above 100, sensitive groups should cut back, and above 150 so should everyone.
No. That is why a green reading and a high pollen day can land together. Forsyth County publishes a separate count and forecast each weekday.
The live map shows it. Forsyth County measures PM2.5 continuously at Hattie Avenue and Clemmons Middle School.
The Forsyth County Office of Environmental Assistance and Protection issues the daily forecast and any Action Day for the Triad. NC DAQ handles the rest of the state.
AQI (Air Quality Index): The EPA's 0 to 500 pollution scale, divided into six color-coded categories from Good to Hazardous.
PM2.5: Fine particulate 2.5 micrometers or smaller. It sets the Winston-Salem AQI outside ozone season.
Michelle Wan is Filterbuy's Brand Manager and Air Quality Writer. She works directly with the manufacturing teams across Filterbuy's four U.S. plants, so her guidance reflects how filters are built and used, not spec sheets. Reviewed by David Clark, Licensed HVAC Technician.
