The term PM2.5 refers to fine particles or droplets of size 2.5 microns are less. This is 30 times smaller than an human hair. These particles are so small that they can reach your blood stream through the lungs.

Where does PM2.5 come from?

These particles come from vehicle exhausts, vehicle brakes, construction, road dust, fuel burning, and industrial operations. PM is a mixture with physical and chemical characteristics varying by location. Common chemical constituents of PM include sulfates, nitrates, ammonium, other inorganic ions such as ions of sodium, potassium, calcium, magnesium and chloride, organic and elemental carbon, crustal material, particle-bound water, metals (including cadmium, copper, nickel, vanadium and zinc) and polycyclic aromatic hydrocarbons (PAH). In addition, biological components such as allergens and microbial compounds are found in PM.

PM2.5  can remain in the atmosphere for days or weeks and thus can transported to long distances by air

How is PM2.5 measured and what is the impact to health?

Long term exposure to these particles cause increase rates of chronic bronchitis, reduced lung function, lung cancer, kidney disease, and diabetes. PM2.5 also contributes to decreased visibility, depletion of soil nutrients, acid rains, and material damages to structures.

PM2.5 is measured in µg/m (micro grams in a cubic meter). WHO recommended guidelines is 10µg/mfor annual average and 25 µg/m3 for 24 hour average. There is no safe level of PM2.5.

Per 10µg/m3 increase of PM2.5 increases mortality risk by the following:

  • All causes: 4%
  • Cardiopulmonary: 6%
  • Lung cancer: 8%

What is the equivalent of number cigarettes smoked?

One cigarette per day is the rough equivalent of a PM2.5 level of 22 μg/m3. Double that level, and it is equivalent to 2 cigarettes per day. Of course, unlike cigarette smoking, the pollution reaches every age group.

What is the  loss in life expectancy due to particulate pollution

Sustained exposure to an additional 10 μg/m3 of PM2.5 reduces life  expectancy by 0.98 years (Source). This is called the  potential years of life lost (PYLL).

PM2.5 Standards

WHO PM2.5 standards

WHO recommended guidelines is 10µg/mfor annual average and 25 µg/m3 for 24 hour average. There is no safe level of PM2.5.

USA PM2.5 standards

The USA standard for PM2.5 (µg/m3  24 hours), category, and health impacts are shown below.

  •  0 to 12.0 – Good
    • Air quality is considered satisfactory, and air pollution poses little or no risk.
  • 12.1 to 35.4 – Moderate
    • Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
  • 35.5  to 55.4 – Unhealthy for Sensitive People
    • Members of sensitive groups may experience health effects. The general public is not likely to be affected.
  • 55.5 to 150.4 – Unhealthy
    • Everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects.
  • 150.5 to 250.4 – Very Unhealthy
    • Health alert: everyone may experience more serious health effects.
  • 250.5 to 500.4  – Hazardous
    • Health warnings of emergency conditions. The entire population is more likely to be affected.

India PM2.5 standards

The Indian  standard for PM2.5 (µg/m3  24 hours), category, and health impacts are shown below.

  •  0 to 30 – Good
    •  Minimal impact
  • 31 to 60 – Satisfactory 
    • May cause minor breathing discomfort to sensitive people.
  • 61  to 90 – Moderately Polluted
    • May cause breathing discomfort to people with lung disease such as asthma, and discomfort to people with heart disease, children and older adults.
  • 91 to 120- Poor
    • May cause breathing discomfort to people on prolonged exposure, and discomfort to people with heart disease.
  • 121 to 250 – Very Poor
    • May cause respiratory illness to the people on prolonged exposure. Effect may be more pronounced in people with lung and heart diseases.
  • 250+ – Severe
    • May cause respiratory impact even on healthy people, and serious health impacts on people with lung/heart disease. The health impacts may be experienced even during light physical activity.

US, India, and WHO air quality standards comparison (for up to 250 µg/m3)