One track paraphrases EPA school guidance for wildfire smoke at each AQI threshold. The other composites school operations from public reporting, district communications, and building records.
Green — AQI 0–50
GUIDANCE
Great day to be active outside. No modifications recommended. Air quality is good and poses little or no risk. Schools participating in the Air Quality Flag Program raise the day's flag based on the forecast at AirNow.gov. Green flag. All outdoor activities proceed as scheduled.
BUILDING
Windows open in the east wing. The HVAC cycles on its normal schedule. Recess runs the full period on the blacktop and the field. The kindergartners line up at the door and go outside. PE class is on the track. The flag out front is green. The air is the air.
Yellow — AQI 51–100
GUIDANCE
A good day to be active outside. Air quality is acceptable. Unusually sensitive students could experience symptoms. Schools should check conditions daily via AirNow.gov. No modifications to outdoor activities are recommended for the general student population.
BUILDING
The front office checks AirNow before first bell. Yellow. A note goes into the weekly parent email about students with respiratory conditions keeping inhalers accessible. The sky looks the same as yesterday from the parking lot. Recess runs the full period. The flag out front is yellow.
Orange — AQI 101–150
GUIDANCE
Sensitive groups should avoid prolonged or intense outdoor exertion. Consider rescheduling outdoor activities or moving them indoors. For all students, reduce long or intense activities. Take more breaks during extended activities such as athletic practice. Ensure the particle filtration system is installed properly and well maintained.
BUILDING
Recess moves to the gymnasium, which was already scheduled for sixth-grade lunch. Sixth-grade lunch shifts to the cafeteria's second rotation. PE runs relay races in the hallway between the library and the front office, cones at each end. Windows close in the main building. In the four portable classrooms behind the parking lot, the window AC units recirculate the same air through the same filters they've run since installation. There is no central HVAC in the portables. Thirty-one percent of public schools use portable classrooms. A parent calls the front office to ask what the school is doing about the air. The office refers them to the district website, which links to AirNow.
Red — AQI 151–200
GUIDANCE
Sensitive groups should avoid all physical activity outdoors. Move activities indoors or reschedule. All students should avoid long or intense outdoor activities. If the building has a forced air system that filters out particles, indoor air quality should be better, and it is appropriate to keep students active inside. Indoor activity is appropriate provided the building's particle filtration system is installed properly and well maintained.
BUILDING
The HVAC in the main building is twenty-six years old and runs MERV 8 filters. The EPA recommends MERV 13 during smoke events. MERV 13 filters are available at the hardware store for $22 each. They will not fit the existing filter housing without modification, and the higher resistance reduces airflow by seven to eleven percent through ductwork designed for lower-grade filters. Upgrading the filtration across the building requires an HVAC technician's assessment the district has not budgeted for. Forty-one percent of school districts need to update or replace HVAC systems in at least half their schools. A custodian runs painter's tape along the base of the loading dock door where daylight shows through the gap. The gym is now recess for K through 3, lunch for 4 and 5, and the only indoor space large enough for a hundred kids to move at the same time. The PE teacher sets up four-square with tape lines on the gym floor between lunch shifts. The NowCast algorithm weights the most recent three hours more heavily during volatile conditions. The number the district checked at 6 a.m. reflected air that no longer exists.
Purple — AQI 201–300
GUIDANCE
Everyone should avoid all physical activity outdoors. Sensitive groups should remain indoors and keep activity levels low. Follow tips for keeping particle levels low indoors.
BUILDING
All exterior doors closed. The front entrance is the only point of entry, opened and closed by hand for each arrival and departure. Interior hallway doors pulled shut to limit air migration between wings. The cafeteria runs three lunch shifts instead of two. Recess is the gym, the cafeteria between shifts, and the library with the tables pushed against the walls. Six hundred and twelve students in a building whose last major renovation was 1998. The average American school building is forty-nine years old. Somebody in the science wing builds a Corsi-Rosenthal box: one box fan, four MERV-13 filters, a cardboard base, duct tape. Cost runs about sixty dollars. A commercial portable air purifier costs ten times that. There are forty-two classrooms. The purchase order for commercial units was not submitted. The Corsi-Rosenthal box sits on a lab table in one room and cleans the air in that room. The portable classrooms have been vacated, their students redistributed to the main building, which adds thirty-one kids to the compressed schedule. Sonoma County's protocol says a school may consider closing at AQI 250. You can smell the smoke inside the building now. Athletic practice was cancelled two days ago. The district website says air quality is being monitored and updates will be provided. The update links to AirNow.
Maroon — AQI 301–500
GUIDANCE
Remain indoors. Keep activity levels low.
BUILDING
The superintendent's phone call comes at 5:45 a.m. or it doesn't. There is no EPA threshold for school closure. There is no federal threshold for school closure. Sonoma County's protocol says a school may decide to close above 300 if the building cannot keep outdoor air from easily entering. The decision belongs to the superintendent, the county health department, the fire agency, and the local air quality management district. In June 2023, schools in New York City opened on a Wednesday morning with no outdoor activities. By that afternoon the AQI reached 342. By 5 p.m. it hit 484. None of those districts had smoke-day protocols before that week. The buses had already run. Elizabeth Public Schools attempted a normal schedule with indoor recess on Wednesday, consulted health officials as conditions worsened, and closed Thursday. When Elizabeth reopened Friday on a half-day schedule, the district recommended face coverings. The closure decision rests on whether the air inside the building is better than the air inside the homes the children will go to if the building closes. Emergency room visits for asthma in New York City nearly doubled during the event, more than 300 cases in a single day. The building has MERV 8 filters and painter's tape on the loading dock door and one Corsi-Rosenthal box in the science wing. The HVAC runs the same cycle it ran at Green. The portables are empty. The gym is four things at once. The windows that opened in the east wing at Green are sealed now, and the air that comes through the ducts comes through the same filters it always did, at the same efficiency it was always rated for, which is not the efficiency the guidance assumes. The flag out front is maroon. There is no flag after maroon.
- The 2024 AQI recalibration: EPA's May 2024 update lowered the PM2.5 threshold for "Good" air from 12 to 9 µg/m³, meaning more days now register as Yellow in communities that previously showed Green.
- 33.5 million children in failing air: The American Lung Association's 2026 State of the Air report found that nearly 2.4 million children with asthma live in counties that received an "F" grade for at least one pollutant, with wildfire smoke and ground-level ozone as primary drivers.
- West Coast smoke-day protocols spreading east: Sonoma County schools have formalized shelter-in-place and closure thresholds by AQI band, while Northeast districts had no smoke-day protocols before June 2023 and improvised decisions in real time as conditions deteriorated.
- The school HVAC funding gap: High-poverty districts rely more heavily on state funding for facilities while the GAO found that an estimated 36,000 schools nationwide need HVAC updates, and the filtration upgrade from MERV 8 to MERV 13 that EPA guidance assumes remains unbudgeted in most districts.