Particulate matter (PM) is a mixture of solid particles and liquid droplets suspended in the air. The number after PM indicates the upper limit of their diameter in micrometres: PM10 particles are no larger than 10 µm, while PM2.5 particles are no larger than 2.5 µm. PM2.5 is part of PM10.
Size matters for health because smaller particles can travel deeper into the lungs. Particle pollution can irritate the airways, trigger asthma and COPD exacerbations, and, with long-term exposure, increase the risk of cardiovascular disease and lung cancer. Some of the smallest particles and their soluble components can pass from the lungs into the bloodstream. Inflammatory responses caused by particle pollution can affect blood vessels and other organs, so the effects are not limited to the respiratory system.
PM2.5 means fine inhalable particles with a diameter of no more than 2.5 µm. They are about 30 times smaller than the diameter of a human hair and can reach the deepest parts of the lungs — the alveoli.
PM2.5 is produced by fuel and biomass combustion and is present in vehicle and industrial emissions, wildfire smoke and smoke from solid-fuel heating. A substantial share forms in the atmosphere through chemical reactions involving gaseous pollutants, so the source of fine particles is not always close to the monitoring location.
PM10 includes all inhalable particles with a diameter of no more than 10 µm, including PM2.5. The larger part of this fraction, between 2.5 and 10 µm, is sometimes called PM10–2.5 or the coarse fraction.
These particles include road and construction dust, soil particles, pollen, and material from tyre, brake and road-surface wear. They are more likely to deposit in the nose, throat and larger airways, but PM10 also includes the fine PM2.5 fraction that penetrates much deeper.
PM2.5 and PM10 are formally distinguished by particle size, while the chemical composition of both fractions varies with their sources. Both measurements describe the mass of a particle mixture in the air, so two identical values in µg/m³ can represent different substances. PM2.5 and PM10 values must not be added together because PM2.5 is already included in PM10.
| Parameter | PM2.5 | PM10 |
|---|---|---|
| Size | Up to 2.5 µm | Up to 10 µm, including PM2.5 |
| Typical sources | Fuel and biomass combustion, smoke, secondary particles, transport and industry | All PM2.5 sources, plus road, construction and soil dust and tyre and brake wear |
| Penetration | Can reach the alveoli; some of the smallest particles and components may pass from the lungs into the bloodstream | The coarse fraction tends to deposit in the upper and larger airways; the PM2.5 within PM10 penetrates deeper |
| Main health concern | Respiratory and cardiovascular effects, lung cancer and premature death | Respiratory and cardiovascular effects; the contribution of the coarse fraction is less well studied than that of PM2.5 |
The 2021 WHO global air quality guidelines set levels that populations should work towards to reduce health risks. The higher the particle concentration and the longer the exposure, the greater the health risk. WHO selected these values from research as targets for reducing population risk, but no completely safe level of particle pollution has been established.
The WHO 24-hour guidelines are defined as the 99th percentile, meaning the corresponding level may be exceeded on approximately 3–4 days per year. Read more about the scientific basis and interim targets on our WHO air quality guidelines page.
| Pollutant | Annual average | 24-hour average (99th percentile) |
|---|---|---|
| PM2.5 | 5 µg/m³ | 15 µg/m³ |
| PM10 | 15 µg/m³ | 45 µg/m³ |
PM concentration is the physically measured mass of particles in the air, expressed in µg/m³ over a specified period. The Air Quality Index (AQI) is a unitless indicator that converts concentration into an easier-to-understand risk scale under the rules of a particular system. Our website uses the US AQI. Its category breakpoints are not WHO guideline levels and are not measured in µg/m³. Learn more on the AQI explanation page.
Sources relevant to Armenia include transport emissions and road wear, heating with wood and other solid fuels, industry, construction, open burning and fires, as well as road and soil dust lifted by wind. The contribution of each source varies by location, season and weather.
WHO and the EPA link particulate matter exposure to respiratory and cardiovascular effects. Risk depends not only on the current reading but also on exposure duration, particle composition, age and health status. The effects below are described in guidance from the WHO and EPA.
Large studies do not diagnose an individual person. They show how often illness and death occur in large groups exposed to different pollution levels. The percentages below describe relative risk: if 100 cases occurred at a lower pollution level, +10% would correspond to about 110 cases in a comparable group at a higher level. It does not mean that every person's individual probability rose by 10 percentage points.
In an updated 2024 meta-analysis, the authors combined cohort studies — observations of large groups of people over months and years. The table shows how each additional 10 µg/m³ of long-term outdoor PM2.5 was associated with mortality. These are causes of death, not the likelihood of first developing each disease.
The figures in parentheses are 95% confidence intervals, showing the statistical uncertainty around each average estimate.
| Mortality category | Change in relative risk per additional 10 µg/m³ of PM2.5 |
|---|---|
| All causes | +9.5% (+6.4% to +12.7%) |
| Ischaemic heart disease | +14.3% (+10.2% to +18.6%) |
| Cerebrovascular diseases, including stroke | +14.6% (+10.1% to +19.2%) |
| Respiratory diseases | +13.6% (+7.9% to +19.7%) |
| Lung cancer | +9.3% (+5.3% to +13.5%) |
According to State of Global Air 2025, based on the Global Burden of Disease study GBD 2023, ambient PM2.5 pollution was associated with approximately 3,700 deaths in Armenia in 2023. The 95% uncertainty interval was 2,870 to 4,580 deaths.
For comparison, Armenia registered 24,313 deaths from all causes in 2023. According to Armstat, more than half were due to diseases of the circulatory system — 12,963 deaths (53.3%). These were followed by malignant neoplasms — 5,054 (20.8%) — and respiratory diseases — 2,083 (8.6%). Together, these three groups accounted for 82.7% of all deaths.
PM2.5 does not appear in these statistics as a separate cause of death. Pollution increases the risk of diseases that are then recorded as the cause, such as heart attack, stroke, lung cancer or COPD. The estimate of 3,700 therefore refers to deaths within these categories; it is not added on top of the total of 24,313.
The same model attributes an estimated loss of 78,400 years of healthy life to this exposure. This measure is called a DALY and combines years lost to premature death with years lived with illness or disability. The calculation included ischaemic heart disease, stroke, COPD, lower respiratory infections, cancers of the trachea, bronchus and lung, type 2 diabetes, adverse neonatal outcomes and dementia.
In the WHO 2025 scorecard for Armenia, the annual average PM2.5 concentration for 2019 was estimated at 34 µg/m³ — almost seven times the WHO guideline of 5 µg/m³. In WHO's broader assessment, which includes both ambient and household air pollution, it was associated with 24% of deaths from stroke and ischaemic heart disease — approximately one in four.
For this analysis, short-term exposure meant exposure lasting from one hour to several days. A systematic review prepared for the WHO guidelines quantitatively analysed 196 publications covering PM2.5, PM10, nitrogen dioxide, ozone and several mortality outcomes. Each additional 10 µg/m³ of PM2.5 was associated, on average, with a 0.65% increase in daily mortality from all causes other than external ones, such as injuries and accidents (95% confidence interval: +0.44% to +0.86%); for PM10 the increase was 0.41% (+0.34% to +0.49%).
These estimates describe changes in daily mortality at the population level, not one person's chance of dying. A fraction of a percent may look small, but across an entire city it corresponds to a measurable increase in deaths. The PM2.5 and PM10 estimates must not be added or used to claim that one particle fraction is precisely a certain number of times more dangerous than the other.
A 2023 Nature study examined lung adenocarcinoma — a common type of lung cancer — associated with changes in the EGFR gene. In mouse experiments and cell models, particles triggered inflammation involving macrophages — immune cells — and the molecule IL-1β. This signal helped cells with a pre-existing EGFR alteration multiply; blocking IL-1β reduced tumour formation.
In this mouse experiment, short-term PM2.5 exposure did not increase the number of mutations in tumours. The results support a different mechanism: pollution may promote the growth of cells that are already altered. The mechanism was demonstrated mainly in animals and cell models, so it cannot automatically be applied to every person.
In 2025, researchers combined cancer-registry data and pollution models for 179 countries. Of approximately 1.26 million new lung adenocarcinoma cases in 2022, 194,864 were estimated to be attributable to ambient particulate pollution.
Asthma. A global 2024 meta-analysis included 25.8 million people from 22 countries and regions. Each additional 10 µg/m³ of long-term PM2.5 was associated with a 21.4% increase in the combined asthma measure among children and 7.1% among adults. That measure combined different outcomes — new diagnoses, prevalence and mortality — and the results varied greatly between studies. The figures show the scale of the association, not an individual's probability of having an asthma attack.
Pregnancy. In a 2021 meta-regression — a comparison of results from several studies that accounts for differences between them — each additional 10 µg/m³ of average ambient PM2.5 during pregnancy was associated with an average 22-gram reduction in birth weight, an 11% higher risk of low birth weight and a 12% higher risk of preterm birth.
Dementia. A 2025 review of 28 long-term studies found an association between PM2.5 and dementia. On the authors' own conservative scale, the evidence received two stars out of five for dementia overall, rated as weak, and three out of five for Alzheimer's disease, rated as moderate.
Check the current air quality. When pollution is high, reduce the duration and intensity of outdoor exercise, especially near roads; people in higher-risk groups should act earlier. At home, reduce outdoor air entering the room when outside air is dirtier and use an appropriately sized air cleaner with a suitable filter. Detailed guidance:
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