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Air pollutants: Particulate Matter

What is particulate matter?

Particle pollution, also called particulate matter (PM), atmospheric aerosol particles or suspended particulate matter (SPM), is defined as microscopic solid (almost always) or liquid materials floating in the air.

Types of particulate matter

Those airborne particles can be divided in suspended particulate matter, thoracic particles, respirable particles, inhalable coarse particles and soot. Inhalable coarse particles can also be classified depending on their size as:

  • Coarse Particles (PM10): aerodynamic diameter from 2.5 to 10 micrometers (µm). To give you an idea, its size is like 1/5 part from a human hair or 1/9 part from a fine beach sand particulate.
  • Fine Particles (PM2.5): 2.5 µm or smaller. For example, it is as little as 1 part from 20 of a human hair, so it is obvious that these particulates can only be seen with an electron microscope.
  • Ultra fine particles (UFPs): less than 100 nanometres (nm). Since they are far smaller, there is no regulation for this size class, even though these are considered to have more severe health impact than the others.

Sources and composition of particulate matter

The composition of particles depends on its origin and formation. Aerosols can occur naturally or artificially.

Most common natural aerosols are pollen or fog, although other natural sources can be volcanoes, sand storms, forest and grassland fires, living vegetation and sea spray.

Human activities such as the burning of fossil fuels, different industrial activities and power plants contribute to produce a significant amount of artificial aerosols. Haze, dust, smoke are just some examples, but there are many more particulate air pollutants.

Since there is a wide range of aerosols’ compositions, here you have summarized some examples:

  • Mineral dust: made of mineral oxides blown from Earth’s crust.
  • Sea salt: originated from sea spray and composed by sodium chloride.
  • Sulfuric acid and nitric acid: generated in the oxidation of primary gases such as sulfur and nitrogen oxides.
  • Organic Matter (OM): deriving from the oxidation of VOCs.

What are the health and environmental effects of particle pollution?

Their capacity to penetrate deeply into your lungs makes particulate matter one of the criteria pollutants to control in order to protect humans’ wellness and health. The smaller the particle is, the more harmful it can be for the organism. This is why particulate matter have different degrees according to its penetration capability into the cardiovascular system:

  • Inhalable particles: can penetrate into the bronchi and are filtered by the cilia.
  • Thoracic particles: can reach easily the bronchioles.
  • Respirable particles: if thoracic particles can even pass throw the alveoli until the bloodstream, then are considered respirable particles.

All those particles have effects on humans health, damaging your lungs and your circulatory system. The most common long-term health effects caused by the inhalation of particulate matter are: asthma, lung cancer, reduced lung function, respiratory diseases, cardiovascular diseases, premature delivery and birth defects (such as low birth weight and premature death).

Exposure to fine particles in the short-term can cause coughing, sneezing, runny nose, shortness of breath and eye, nose, throat and lung irritation.

Huge concentrations of particles in the air can lead to haze creation or difficulties in the photosynthesis functions of plants. Furthermore, depending on their composition they can react with other compounds to create other harmful gases for the environment or and the people.

How is particulate matter air pollution controlled?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Both sizes of particulate matter, PM10 and PM2.5, are classified as a primary and secondary criteria pollutants since it can be extremely harmful for all living beings. Maximum permitted or recommended levels for PM are:

  • In PM2.5:
    • World Health Organization (WHO) guidelines: 25 μg/m³ per day (which cannot be exceeded more than 3 days/year) and 10 μg/m³ per year.
    • NAAQS: maximum concentration of 35 μg/m³ daily and annual mean of 12 μg/m³.
    • EU Air Quality Directive: only monitoring annual concentration, which cannot be higher than 25 μg/m³.
  • In PM10:
    • World Health Organization (WHO) guidelines: 50 μg/m³ per day (which cannot be exceeded more than 3 days/year) and 20 μg/m³ per year.
    • NAAQS: 150 μg/m³ and can only be exceeded more than once per year on average over 3 years.
    • EU Air Quality Directive: cannot exceed more than 35 times annually the concentration of 50 μg/m³ every 24 hours. There is also a maximum of 40 μg/m³ per year.
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