What is Particulate Matter (PM2.5)?

Particulate matter (PM) is composed of solid and liquid particles suspended in the air. The scientific definition of PM is not based on the composition of the pollutant but is based on the size of the particles.

• PM10, the largest category, includes all particles with a diameter of 10 micrometers or less.
• PM2.5 includes particles that are less than 2.5 micrometers in diameter.
• PM0.1 or nano particles are less than 0.1 micrometers in diameter.

Generally, the smaller the particle size the worse the potential health impact. The smallest particles (nano-particles) can easily infiltrate any part of the body, including the arteries, lymph nodes, heart, liver, spleen or even the brain. There is some evidence to suggest that nano-particles cluster around existing inflammations / fatty deposits in arteries, which may lead to cardiovascular events.

There are 3 main sources of PM:

1. Natural aerosols – include sea salt, volcanic ash, pollen and sand dust among others
2. Primary PM – directly emitted into the air as solid particles; includes black carbon from burning fossil and solid fuels and also includes tiny shard of Lead, emitted from cars due to the use of Tetra-ethyl Lead as an anti-knocking agent
3. Secondary PM – formed by chemical processes in the air; includes Sulphur Dioxide from burning coal and high Sulphur-diesel and Ammonium Nitrate formed as a result of Ammonia gas from vehicles reacting with Nitrogen Oxides (NOx) in the air

Not all PM is created equal. High PM level due to sea salt is benign as compared to the same PM level driven by toxic chemicals in the air. Hence, each location/city has its own unique PM fingerprint. Moreover, in some locations the PM is locally generated and in others it travels miles to get there.

PM2.5 is measured in micro-grams (one-millionth of a gram) per cubic meter (mg/m3).