PM2.5 and PM10 ¿What Is The Difference?

The particulate matter (PM); previously, I have discussed a bit about the composition of the air pollution, and it is clear that particulate matter is a principal component of it. So, it is crucial to recognize the difference between the PM2.5 and PM10 terms to understand the composition of the air pollution. Particulate matter is a classification that includes a vast chemical compound number, ions, and elements. Differentiating them by size, molecules smaller than 2.5 and 10 micrometers; the PM10 group includes the PM2.5 classification and other compounds of less than 10 micrometers. The size is a determining factor for the absorption of chemicals by the body; studies show that smaller molecules or particles can transport without problem, acquiring a greater capacity to make people sick. The particulate matter describes a mixture of solid particles and liquid droplets found in the air - that's what some people call particulate pollution. Some particles, including dust, dirt, soot, or smoke, are large or dark enough to be seen with the eye; others need to be detected using a microscope due to their small size. A clear example is a fire, see Image 1, when burning wood or materials, the chemical reaction generates the release of smoke and ash, both considered pollutants that affect health.

Image 1: The smoke and ashes produced in fires are a significant source of particulate material and other air pollutants.Image 1: The smoke and ashes produced in fires are a significant source of particulate material and other air pollutants.

The fraction of particulate matter found in the analysis of air pollution is a mixture and its percentage composition varies by location, depending on the sources of pollutants in that area and topology. PM10 and PM2.5 share some components in both groups which include sulfates, nitrates, ammonium, magnesium and chloride, organic and elemental carbon, crustal material, sodium, potassium, calcium, 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. The particle pollution includes:

PM10: inhalable particles with diameters of 10 micrometers and smaller; PM10 particles are small enough to get into the throat and lungs, high levels of PM10 cause cough, nose run, and eyes sting.  People with heart or lung conditions might have more symptoms when PM10 levels are high; including wheezing, chest tightness, or difficulty breathing. Mineral dust (MD), organic matter (OM), sea salt (SS), secondary inorganic aerosol (SIA), and other dust are big contributors to the PM10 fraction;  secondary inorganic aerosol and Organic matter are major components of PM10, high contributions of mineral dust are also found. The secondary inorganic aerosol includes ammonium (NH4+), nitrate (NO3-), and sulfate (SO4 2-), ammonium nitrate (NH4●NO3), and ammonium sulfate (NH4)2●SO4), which are formed by the neutralization of nitric acid, (HNO3) and sulfuric acid (H2SO4). Organic matter fraction includes UCM (an unresolved complex mixture), saccharides, alkanoic acids, alkanes, alkanols, PAHs (Polycyclic aromatic hydrocarbons), hydroxy-PAHs, and other tracers. The photochemical formation and other chemical reactions have an influence on the composition of PM10, but the reactions and thermodynamics will be discussed in another article.

Image 2: The sand and powders present many particle sizes.The sand and powders present many particle sizes.

PM2.5: fine inhalable particles, with diameters of 2.5 micrometers or less; includes small molecules, elements, and ions. PM2.5 is small enough to penetrate to the lungs and invade even the smallest airways. A human hair is 30 times larger than the largest fine particle. PM2.5 are tiny particles in the air that reduce visibility and cause the air to appear hazy when levels are elevated. Outdoor PM2.5 levels are most likely to be elevated on days with little or no wind or air mixing. Some constituents include Vanadium (V), Manganese         (Mn), Nickel      (Ni), Copper (Cu), Cadmium                (Cd), Barium      (Ba), Lead           (Pb),  Chlorine  (Cl-), Nitrate       (NO3-), Sulfate (SO4),   Sodium (Na+),                Nitrogen Hydride (NH4+), Potassium (K+),  Magnesium (Mg2+),  Calcium (Ca2+),           organic carbon (OC), elemental carbon         (EC),  Aluminum (Al), Arsenic (As), among others. Organic compounds in the extracts of PM2.5 together with trace heavy metals would potentiate the toxic effects on cells

These pollutants and their raw material sources share the ability to remain in the air and the characteristic of easily disaggregating into various particle sizes, the second being the reason why some chemicals are shared between PM-groups; this change according to the materials and the environmental characteristics of the polluted places. Although the size difference between PM10 and PM2.5 is about 7.5 microns, the difference in the potential damage to the body is remarkable as they decrease in size. The effects on health change according to particle size, as can be seen in Image 2, smaller sizes tend to spread easily and cause greater damage throughout the body, but they are not exclusive, since it has been shown that certain chemicals can have a greater range than others.

Image 3: Comparison between the particulate matter and the possible damage site to the human body.

PM Group

Diameter

Site

PM 10

Coarse Particles

Upper respiratory tract

PM 2.5

Fine Particles

Lower respiratory tract

PM 1

Very Fine Particles

Alveolus

PM 0.1

Ultrafine Particles

Whole-body

Suspended in the air, the particulate matter enters our bodies through the respiratory tract. PM10, as is it bigger, is more likely to deposit on the surfaces of the larger airways of the upper region of the lung, while PM2.5 is more likely to travel farther and deposit on the surface of the deeper parts of the lung. So, PM10 tends to cause obstruction and damage, mostly in the upper respiratory passages; while PM2.5 affects both the upper and lower respiratory tract. At the same time, it is recognized that both groups can reach the bloodstream by passive and active transport. Smaller particles, such as PM1 and PM0.1, become even more harmful and have the ability to spread even more easily through the lungs into the blood and organs, having a greater range and increasing the risk. In addition, particulate material with a diameter between 0.1 microns and 1 micron can remain in the atmosphere for days or weeks and be subject to long-range transport in the air, therefore, highly industrialized areas have the capacity to affect populations and nature located at a great distance; this transport can take place even between countries, and in some cases between continents such as the case of Sahara sands in Latin America. In highly-affected countries by air pollution, products and processes that greatly influence the production of particulate matter have been prohibited and criminalized, controls such as internal air purifiers in buildings, confinement on days of high outdoor pollution, and promoting the indoors-outdoors cultivation of plants to purify the air are taken to protect the population. Interest is provided for the investigation of their solutions, yes, but economic gains are still prioritized by continuing to use products and processes that are unsafe for the population and the environment.

References
  • CARB. Inhalable Particulate Matter and Health (PM2.5 and PM10). California Environmental Protection Agency
  • EPA. Particulate Matter (PM) Pollution. Unites States Environmental Protection Agency.
  • Zhang HH, Li Z, Liu Y, et al. Physical and chemical characteristics of PM2.5 and its toxicity to human bronchial cells BEAS-2B in the winter and summer. J Zhejiang Univ Sci B. 2018;19(4):317-326. doi:10.1631/jzus.B1700123.
  • Sarkawt M.L. Hama, Rebecca L. Cordell, Jeroen Staelens, Dennis Mooibroek, Paul S. Monks. Chemical composition and source identification of PM10 in five North Western European cities. Atmospheric Research. Volume 214. 2018. Pages 135-149. ISSN 0169-8095. https://doi.org/10.1016/j.atmosres.2018.07.014.
  • WHO. Health effects of particulate matter. World Health Organization. 2 May 2018. Link https://www.euro.who.int/__data/assets/pdf_file/0006/189051/Health-effects-of-particulate-matter-final-Eng.pdf.

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