The main thing to remember:
PM2.5 measures harmful fine particles (smaller than 2.5 micrometers) in µg/m³ — a direct indicator of health risks as they enter the lungs and blood.
The AQI (Air Quality Index) is a colorful, country-specific index (0–500) that translates the concentration of pollutants like PM2.5 into simplified health risk levels.
Use AQI for a quick overview of hazard , but rely on PM2.5 for a universal assessment of pollution : a level of 40 µg/m³ may be considered “moderate” in one country and “unhealthy” in another.
What is PM2.5? The invisible pollutant explained
Define fine particles
PM2.5 refers to suspended particles with a diameter of less than 2.5 micrometers — 30 times finer than a human hair .
These microscopic pollutants, invisible to the naked eye, represent a major health risk . Their tiny size allows them to cross the respiratory tract , reach the pulmonary alveoli , and then enter the blood .
This intrusion causes inflammation , respiratory problems and long-term cardiovascular damage , making PM2.5 a silent but formidable threat .
Short-term exposure may worsen asthma or respiratory infections.
In the long term, it is associated with decreased lung development in children , chronic heart disease , and premature mortality .
Children , the elderly and those with pre-existing illnesses are the most vulnerable, as their bodies filter these particles less effectively.
Sources and measurement of PM2.5
PM2.5 comes mainly from combustion processes : exhaust gases , power plants , fires , or industrial emissions .
Household activities such as cooking or scented candles also produce them.
These particles form a complex mixture of organic compounds, metals and sulfates — diesel engines being responsible for more than 90% of particles smaller than 1 micron .
Scientists measure PM2.5 with beta attenuation analyzers , which calculate the mass concentration in micrograms per cubic meter (µg/m³) .
Unlike an abstract index, this measure gives a concrete value of the pollution level.
For example, a rate of 35 µg/m³ means that 35 millionths of a gram of particles are present in every cubic meter of air breathed — a tangible and worrying reality.
What is AQI? Your daily air quality report
The Air Quality Index (AQI) acts as a report card for air pollution.
It translates complex environmental data into understandable values .
Unlike raw measurements, this calculated scale converts pollutant concentration into health risk levels .
It's a bit like air quality weather , which helps everyone adapt their outdoor activities .
Understanding the Air Quality Index
The AQI is not a direct measure of pollution, but a mathematical translation of multiple pollutants into a single score .
This standardized scale ranges from 0 to 500 in the United States (with equivalents in other countries).
PM2.5 often influences the final result, as it poses the most serious health risks .
The interest of the AQI is to make the invisible visible thanks to a universal color code .
How AQI works
This index combines six main pollutants: PM2.5 , PM10 , ozone , sulfur dioxide , nitrogen dioxide and carbon monoxide .
Each concentration is converted into a sub-index , and then the highest determines the final AQI value.
The colors, from green (0–50) to burgundy (301+) , allow you to instantly identify the danger level .
While PM2.5 often weighs heavily in the calculation, the composite system prevents a single pollutant from dominating the perception of risk.
Differences between AQI and PM2.5
Why track both PM2.5 and AQI ?
It's a bit like comparing the actual temperature and the perceived temperature .
PM2.5 is a direct and scientific measurement of particulate matter in the air.
For example, 10 µg/m³ of PM2.5 represents the same concentration whether you are in Paris or Tokyo .
The AQI translates this data into an interpretable index , combining several pollutants to indicate the overall health risk .
But be careful: an AQI of 150 in New York does not have exactly the same meaning as an AQI of 150 in Beijing , each country using its own calculation formula.
PM2.5 vs AQI: Quick Comparison
| Characteristic | PM2.5 | AQI (Air Quality Index) |
|---|---|---|
| Definition | Direct measurement of fine particle concentration | Calculated index representing overall air quality |
| Unit | µg/m³ (micrograms per m³) | Numerical scale (0–500) |
| Indication | Exact amount of a specific pollutant | Overall health risk level |
| Universality | Universal scientific value | Varies by country |
In summary:
PM2.5 reveals the reality of pollution , while AQI indicates how to react .
PM2.5 vs PM10: Understanding the Difference
PM10 includes all particles ≤ 10 microns, while PM2.5 (≤ 2.5 microns) is its finest and most dangerous subcategory .
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Sources :
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PM2.5: combustion (vehicles, factories, fires).
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PM10: mechanical dust (construction site, agriculture, pollen, sand).
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Health effects :
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PM10: Often stops in the nasal passages or throat, causing irritation and asthma.
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PM2.5: penetrates deep into the lungs and blood, causing heart disease , lung cancer and premature death .
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Monitoring both allows public policies to be adapted:
reduce PM2.5 = limit emissions.
Reduce PM10 = Control dust and outdoor activities.
Practical tips to protect your health
Inside
Indoor air can be 2 to 5 times more polluted than outdoor air.
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Use a HEPA air purifier : it captures 99.97% of particles ≥0.3 µm, including PM2.5.
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Close windows during pollution peaks, but ventilate briefly when the AQI is below 50.
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Avoid internal sources : candles, tobacco, unventilated gas.
Outside
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Check the forecast (AirNow, WAQI).
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Avoid intense physical exertion when the AQI exceeds 150.
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Wear a filtering mask (N95/FFP2).
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Favor morning activities , when PM2.5 concentrations are lower.
The R-PUR mask: the high-performance benchmark against air pollution
Designed and manufactured in France, the R-PUR anti-pollution mask represents one of the most advanced levels of protection in the world. Thanks to its FFP3+ filter capable of capturing ultrafine particles down to PM0.05 , it offers a barrier far superior to traditional standards such as N100 or FFP3.
Its innovative multi-layer system combines filtration and activated carbon , neutralizing both solid particles (dust, pollen, exhaust gases) and toxic gases (NO₂, CO, ozone, VOCs).
Designed for everyday use, the R-PUR mask combines technology and comfort : its memory foam perfectly adapts to the contours of the face to ensure an optimal seal , while remaining breathable even during prolonged wear. Lightweight, ergonomic and elegant, it protects your airways without compromise - a sustainable solution for facing urban pollution with complete peace of mind.
Discover the anti-pollution mask from R-PUR.
FAQ
How Does PM2.5 Relate to the AQI?
PM2.5 is a key component used to calculate the Air Quality Index (AQI). While the AQI is a color-coded scale combining multiple pollutants (including PM2.5, PM10, ozone, and others), PM2.5 specifically measures fine particulate matter. Governments convert PM2.5 concentrations (in µg/m³) into AQI values using non-linear formulas to reflect health risks. For example, a PM2.5 level of 35 µg/m³ might translate to an AQI of 100 in the U.S., signaling "Moderate" risk. This relationship helps simplify complex pollution data into actionable health guidance.
Are PM and AQI the Same Thing?
No, they’re fundamentally different. PM2.5 is a direct measurement of fine particulate matter (in micrograms per cubic meter), while the AQI is a calculated index that aggregates pollutants into a single number (0-500 scale) with health risk categories. Think of PM2.5 as the "raw data" (like temperature) and AQI as the "weather forecast" (like "hot" or "cold"), interpreting that data for daily decisions.
What Does "PM2.5" Mean on an Air Purifier?
On air purifiers, PM2.5 indicates the device’s ability to capture particles smaller than 2.5 micrometers. Look for HEPA filters, which trap 99.97% of PM2.5. Many purifiers display real-time PM2.5 readings to show indoor air quality improvements. Lower µg/m³ values mean cleaner air, aligning with WHO’s annual guideline (5 µg/m³).
At What AQI Level Is Air Quality Unhealthy?
The EPA defines "Unhealthy" AQI as 151-200, urging sensitive groups (asthma patients, children, elderly) to limit activity. At 201-300 (Very Unhealthy), everyone should avoid prolonged outdoor exertion. For context, 99% of the world’s population lives in areas exceeding WHO’s stricter PM2.5 guideline (5 µg/m³), highlighting widespread risk.
