Particulate matter (PM) is an air pollutant composed of tiny solid and liquid particles. But what exactly are these particles? Read on to find out.

What is particulate matter?

Particulate matter is classified by the size of its particles. PM10 consists of coarse particles that have diameters that are less than or equal to 10 micrometres, while PM2.5 are fine particles with diameters less than or equal to 2.5 micrometres. For scale, the human hair has a diameter of roughly 70 micrometres. There are also newer classifications such as PM0.1, PM0.3, PM0.5, PM4, and PM5, but the aforementioned PM2.5 and PM10 are the main ones.

Where does particulate matter come from?

Primary particulate matter is emitted from a direct source, such as power plants, factories, vehicles, construction sites, forest fires, volcanos, dust storms, stoves, and heaters.

On the other hand, secondary particulate matter is formed as a result of chemical and physical reactions with compounds such as sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3), and volatile organic compounds (VOCs). This occurs through a process called nucleation, where the gaseous molecules of ammonia condense to form either liquid or solid particles suspended in the atmosphere.

What is particulate matter made up of?

Components of primary particulate matter are:

  • Sodium chloride (sea salt)
  • Elemental carbon (soot) from fossil and biomass fuel combustion
  • Trace metals (lead, cadmium, copper, nickel, chromium, zinc, manganese, vanadium) from metallurgical processes, industry fuels, and mechanical abrasion processes
  • Mineral components (aluminum, silicon, iron, calcium) from construction, demolition work, and quarrying

Components of secondary particulate matter are:

  • Sulfate, which is formed by the oxidation of SO2 to sulfuric acid (H2SO4) reacting with NH3 to form ammonium sulfate ((NH4)2SO4)
  • Nitrate, which is formed by the oxidation of NOx to form nitric acid (HNO3) reacting with NH3 to form ammonium nitrate (NH4NO3). It can also react with sodium to form sodium nitrate (NaNO3)
  • Water, from the atmospheric water taken by (NH₄)2SO4 and NH4NO3 during the chemical reaction

Both primary and secondary PM can also consist of organic carbon compounds, of which there are two types: primary organic carbon comes from traffic or industrial combustion processes, while secondary organic carbon is from the oxidation of volatile organic compounds (VOCs). Examples include aliphatic and aromatic hydrocarbons, heterocyclics and oxygenates (aldehydes, ketones, and carboxylic acids.

Why is particulate matter dangerous?

Particulate matter is linked to cardiovascular and respiratory diseases such as asthma, bronchitis, emphysema, and even cancer. It has been found that the smaller the particle, the higher the health risk because of its ability to penetrate deeper into the body. Generally, PM10 irritates the eyes, nose, and throat, while PM2.5 is able to penetrate deep into the respiratory and circulatory systems, thus causing damage to the lungs, heart, and brain.

What can I do to reduce my exposure to particulate matter?

Knowing the levels of pollutants in the air you breathe is the best way to take care of your health. You can do this by viewing your local air quality index (AQI) through your regional or federal government website. Ideally, you will receive information on how the measurements are gathered, how the index is calculated, air quality trends and analyses, and current air pollution policies. However, air quality data is traditionally gathered only at a few limited locations, which that available data is most likely coming far away from the places that matter most to you.

An alternative is for you to volunteer as an air quality sensor host. By allowing sensors to be installed on your own premises, you help provide accurate air quality information on our free citizen portal for governments and people like you. The more local air quality information there is, the better the clean air actions that can be taken for a healthier life. Join our sensor host programme today!