Not all particulate matter is equal – why some particulates are more dangerous than others

Particulate matter (PM) is an air pollutant composed of tiny solid and liquid particles. Primary particulate matter is emitted from a direct source, while secondary particulate matter is formed as a result of chemical and physical reactions with various compounds. Particulate matter is classified based on the size of its particles, of which there are two main types: PM₁₀ (coarse particles with diameters less than or equal to 10 micrometres) and PM_2.5 (fine particles with diameters less than or equal to 2.5 micrometres). Particulate matter is dangerous because it is linked to cardiovascular and respiratory diseases. The smaller the particle, the higher the health risk because of its ability to penetrate deeper into the body. PM₁₀ is generally an irritant, while PM_2.5 is what damages the lungs, heart, and brain by penetrating deep into t he respiratory and circulatory systems. However, not all particulate matter is the same. Some are in fact deadlier and cause more harm than others apart from size. Why? The answer lies in its composition. 

Why are some particulate matter more dangerous than others?

In 2009, research showed that inhaling particles consisting of metal and carbon leads to increased illnesses and deaths from cardiovascular and respiratory diseases due to acute stress on the lungs and heart through inflammation. It was not the total level of particulates that mattered, but the existence of these specific components. The main source of metals such as nickel and vanadium in urban areas come from space heaters in older apartment buildings, while carbon particles are a byproduct of diesel exhaust from vehicles. Traffic is also an important source of metals and carbon due to brake and tire abrasions and roadway dust. 

In comparison, natural sources of PM include desert dust (silicate minerals and carbonates), sea spray (sodium chloride), volcanic ash (primary PM and secondary PM from sulfur dioxide), and wildfires (PM₁₀). PM consisting of sand and salt tend to be larger in size, and are thus unable to travel as deep into the body to cause serious harm. Specifically, the mineral composition of desert dust makes it less likely to attack mucous membranes or contain carcinogenic substances. PM from wildfires, however, are a different story, which will be covered below.

The findings from 2009 are further expanded in what researchers at the Paul Scherrer Institute PSI discovered in 2020: that the oxidative potential of particulate matter is what makes it more harmful. “Oxidative potential” is the ability of PM to reduce the amount of antioxidants in the body, which can lead to cell and tissue damage. When cells are under stress, they signal the immune system to initiate inflammatory responses in the body. The study showed that PM with an elevated oxidative potential intensified the cells’ inflammatory reaction, which in turn increased the risks of cardiovascular and pulmonary diseases through a process known as “oxidative stress”. The oxidative potential of PM is mostly determined by anthropogenic secondary organic aerosols from residential biomass burning such as wood combustion and coarse-mode metal emissions from vehicular brake and tire wear. Hence, populations in urban areas are exposed to both a higher amount of particulate matter as well as particulate matter with a higher oxidative potential. In addition, the non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_x) released by wildfires can also undergo photochemical reactions to produce secondary organic aerosols. 

Aside from the oxidative potential of particulate matter that makes it more harmful, there are also carcinogenic components that make certain particulates pose a higher risk to health. These include black carbon and polycyclic aromatic hydrocarbons (PAH) from incomplete combustion and burning of fossil fuels and wood, which can be produced in wildfires. Hence, particle composition in addition to smaller particle size is what makes certain PM more harmful than others.

What can be done against particulate matter?

Based on current evidence, urban sources of particulate matter are the most harmful to human health. The best way to thus tackle them is through targeted actions and policies by authorities and industries in the areas of transport, land planning, public health, housing, and energy sectors. This can be done by reducing the sources of PM (power plants, vehicle traffic, construction sites, indoor stoves and heaters), or by tackling immission by trying to remove it from the air (filters, nanoparticle street coating, fountains, etc.).

To begin, a reliable urban air quality monitoring network is essential in order to track and monitor the areas most affected. Breeze Technologies offers just that. Our air quality management solution enables cities to achieve an arbitrarily high data density for perfect insights. Breeze’s sensors are much smaller than traditional air quality monitoring equipment, averaging at just 3.5 inches in diameter. Cloud-enabled and affordable, they allow for easy and efficient installation in public spaces, at street lights, and on city infrastructure. Data is collected in real time, with data points available up to every 30 seconds for the highest accuracy and reliability through historical and location-based geo-spatial analyses. This information can be used to assist in evidence-based urban planning, chemical transport models, and traffic management – all of which will prove invaluable in combating particulate matter emissions to populations that are most at risk. Contact us today for more details!