What is PM10 — and why it dominates Gulf air quality

PM10 is airborne particulate matter up to 10 micrometers across, roughly a seventh the width of a human hair, and it's the pollutant that defines a bad-air day in the Gulf. Unlike the fine smoke and traffic particles that dominate air-quality headlines in most other regions, Gulf air is shaped first and foremost by coarse, wind-blown mineral dust, which lands squarely in the PM10 size range.

What "PM10" actually measures

Particulate matter is classified by size, not by what it's made of. PM10 covers particles up to 10 micrometers in diameter; PM2.5, the finer category most commonly cited in Western air-quality reporting, covers particles up to 2.5 micrometers. Both are measured in micrograms per cubic meter of air and both are tracked by every major air-quality standard, including the US EPA framework Nafas uses to translate a forecast into a severity band.

The size distinction matters because it maps to where the particles come from and how they behave. PM2.5 is small enough to stay suspended for a long time and is produced mainly by combustion: vehicle exhaust, industrial burning, wildfire smoke. PM10 includes everything PM2.5 does, plus a coarser fraction: dust, pollen, sea salt, construction debris — the kind of particle a sandstorm throws into the air by the ton.

Why the Gulf is a PM10 story first

Most global air-quality products, and most air-quality journalism, were built around cities where PM2.5 from traffic and industry is the dominant health concern. The Gulf's geography inverts that. The region sits next to some of the largest arid and semi-arid dust source areas on Earth, and prevailing regional winds routinely lift and transport mineral dust across the whole coastline, on top of whatever local traffic and construction dust a city generates on its own. PM10 readings in Gulf cities can spike well beyond what a comparable city elsewhere would ever see from combustion sources alone, precisely because dust events add a coarse-particle load that smoke-driven models weren't built to anticipate.

That's the practical reason a forecast tuned for European or North American air quality doesn't automatically transfer well to Abu Dhabi or Riyadh: the thing driving the worst days is a different kind of particle, moved by different physics — wind picking up sand, not a fire or a highway.

How Nafas turns PM10 into a decision

Nafas reads hourly PM10 and PM2.5 forecasts for each city from Copernicus CAMS (via Open-Meteo), then scores every hour against the US EPA's AQI breakpoints — the 2024 PM2.5 update, applied consistently across every city and every forecast run, so the same number always means the same thing. Six severity bands run from Good through Hazardous; whichever pollutant is worse in a given hour, PM10 or PM2.5, sets that hour's band. From there, a rule-based layer looks for the worst stretch of hours in the next day and writes it up in plain language: not "PM10 forecast: 210 µg/m³," but "move outdoor events indoors, hazardous dust 6–11am, clears by 2pm."

The point isn't to replace the number, it's to answer the question the number raises. See the explainer on how that advice line gets written, or check today's live forecastfor any of the 10 Gulf cities Nafas covers.