How to read the table above
Each city shows a current air quality index on the US EPA scale, stamped with the time the feed was built. Read that timestamp: the feed is rebuilt once a day, and the days air quality moves fastest — a fire upwind, ash drifting — are the days an old estimate is least useful.
Where these numbers come from — modelled, not measured
The index above is Open-Meteo’s us_aqi field, from the Copernicus CAMS atmospheric model, interpolated to each city’s coordinates. It is a model estimate, not a station reading — there is no instrument at most of those eight points. We do not compute the index; we store what the model returns, on the EPA scale.
Guatemala’s measured air quality comes from INSIVUMEH, which runs a national ground-station network and publishes a daily Índice de Calidad del Aire bulletin (PDF, Spanish) with PM10, PM2.5 and ICA per station, plus live station dashboards. Where the two disagree, the station is the measurement and the model is the estimate.
They are not the same quantity either — the bulletin is a daily mean per station, the table above a current value — so expect them to differ. INSIVUMEH computes its ICA with the EPA methodology (EPA-454/B-18-007), so the bands below are the same ones. One trap in the Spanish bulletin: translate by the ICA number, not the words. Muy Mala is ICA 151–200, EPA’s Unhealthy — not Very Unhealthy, a band more severe.
The EPA bands, and what WHO says about the same air
The US EPA’s description of each band, verbatim from AirNow:
| Band | EPA’s description |
|---|---|
| Good (0–50) | “Air quality is satisfactory, and air pollution poses little or no risk.” |
| Moderate (51–100) | “Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.” |
| Unhealthy for Sensitive Groups (101–150) | “Members of sensitive groups may experience health effects. The general public is less likely to be affected.” |
| Unhealthy (151–200) | “Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.” |
| Very Unhealthy (201–300) | “Health alert: The risk of health effects is increased for everyone.” |
| Hazardous (301+) | “Health warning of emergency conditions: everyone is more likely to be affected.” |
The WHO 2021 air quality guidelines set stricter reference points: PM2.5 at 5 µg/m³ annual and 15 µg/m³ over 24 hours; PM10 at 15 µg/m³ annual and 45 µg/m³ over 24 hours. Those are health-based exposure guidelines, not a communication index: a city can sit in EPA’s Moderate band and be above the WHO 24-hour PM2.5 guideline the same day. WHO singles out PM2.5 because, where both fractions penetrate deep into the lungs, PM2.5 “can even enter the bloodstream”.
What drives Guatemala’s air
INSIVUMEH’s response protocol names the recurring causes: Saharan dust, forest fires, and point sources — eruptions, localised fires, landfill fires. Two everyday drivers sit on top.
Vehicles, concentrated in the capital. SAT’s vehicle-registration microdata (August 2026 release) sums to 6,709,409 vehicles registered with SAT between 1980 and August 2026; motorcycles are 48.9%, and 34.5% carry a model year of 2009 or earlier. That is cumulative registrations, not vehicles on the road — the dataset has no de-registration signal. Per state news agency AGN, reporting MEM, diesel’s sulphur limit fell from up to 500 ppm to 15 ppm on 1 June 2026.
Cooking smoke, concentrated outside it. WHO’s Global Health Observatory puts the share of Guatemalans relying primarily on clean cooking fuels at 51% [36–65] in 2024 — 74% [56–89] urban, 21% [8–39] rural. WHO adds that in poorly ventilated dwellings, “indoor smoke can have levels of fine particles 100 times higher than acceptable” — exposure no outdoor index can see.
Rain is the switch. INSIVUMEH states it directly: precipitation is the main removal process for PM10 — which is why air degrades through the dry season (see the weather hub) and recovers when the rains return.
The burning season and ash days
CONRED reports the 2026 fire season began on 1 January; by 17 February the worst-hit departments were Guatemala (59 incidents), Quiché (36) and Sacatepéquez (29), and by 4 May it counted more than 1,280 incidents and over 19,650 hectares nationally. CONRED puts 2025 at more than 1,700 fires and 40,000 hectares, says most incidents relate to human activity, and advises against burning and slash-clearing on slopes.
Ash is the other spike. INSIVUMEH has reported Fuego ash columns to 5,000 m above sea level dispersing roughly 40 km west, with ashfall in communities such as San Pedro Yepocapa. Those are the days the table above is most likely to be wrong: a plume is narrow and fast-moving, and a once-daily model value at a city centre will not catch it. On an ash day use today’s volcano status, the Fuego tracker, the volcanic ash advisories page and the volcano hub, then the INSIVUMEH bulletin.
What to do at each level
The bands above say who is affected; the actions follow. Good: nothing. Moderate: only unusually sensitive people need to pay attention. Unhealthy for Sensitive Groups: those groups should ease off outdoor exertion, while the general public is less likely to be affected. Unhealthy: that widens to some of the general public. Very Unhealthy is a health alert for everyone; Hazardous is an emergency warning.
INSIVUMEH’s published recommendation during a degraded-air event is short: if you are outside your home, wear a mask at all times to reduce inhalation of pollutants, and follow whatever measures CONRED and the Ministry of Health (MSPAS) consider necessary. Its escalation ladder says how often to expect news: a special bulletin every 12 hours at red level, every 6 hours at purple, every 4 hours at brown.
If symptoms, not a number, brought you here — a child with asthma, a cough that will not settle — the index is the wrong instrument. See healthcare options.