Definition of Particulate Matter

Raquel Tamara Saavedra Pino
Enviromental chemistry. Master in Chemistry

Particulate matter (PM) corresponds to the solid fraction of the atmospheric aerosol, usually differentiated according to size in 4 fractions (PTS, MP10, MP2.5 and MP1), and corresponds to an aggregate of various compounds.

Its origin and incorporation into the atmosphere is associated with natural, biogenic and anthropic sources. These particles can retain their original conformation or undergo chemical transformation processes, giving rise to a differentiation of primary PM and secondary PM respectively.

These particles are considered dangerous for the health of people and the environment. environment because they present carcinogenic and mutagenic compounds in their aggregation, in addition to interfering with the albedo and cloud formation nuclei.

MP Classification

The MP is classified according to size, which is represented by the aerodynamic diameter, this being a standardization for ideal spherical particles of equivalent density and the same speed deposition.

The PM size distribution ranges from 0.005 µm to 100 µm, and two types of particle fractions are distinguished: fine (< 1 µm) and coarse (< 100 µm). Within the first, we can mention particles with a diameter of less than 1 µm (PM1.0) and 2.5 µm (PM2.5), on the other hand, the second It covers the fractions greater than 1um of the total suspended particles (PTS), of the particulate material less than 10 µm (PM10) and of the MP2.5.

Incorporation and Origin

It can be incorporated into the atmosphere through physical or chemical processes (natural sources), biological (sources biogenic), or through the result of emissions from the development of human activities (sources atopic).

Within the natural sources, the soil turns out to be one of the main sources of origin of coarse particles, being the chemical composition and size distribution of these depending on the geological characteristics and wind speed of the zone. Another important source of coarse particles is marine aerosol, consisting mainly of sodium chloride (NaCl) and sulfates. (Na2SO4, MgSO4 and K2SO4), in addition to volcanic emissions is forest fires, whose contributions are limited in time and space.

The biogenic sources form the bioaerosol, which is constituted mainly by plant remains, pollen, spores and microorganisms (including viruses, bacteria, fungi and algae), and mainly make up the thick MP.

Particles of anthropogenic origin are mainly associated with urban and industrial areas, and come from agricultural and industrial activities (construction, mining, foundries, brick factory etc.), vehicular transport, combustion of materials and fuel, in addition to erosion processes. For this type of emissions, the particle size range is very diverse.

secondary PM

Atmospheric aerosols are classified into primary and secondary, depending on whether the particles are emitted to the atmosphere directly, or if they are generated by chemical reactions of the atmosphere.

Particles and gases of biogenic origin, such as sulfur dioxide, dimethyl sulphide, nitrogen oxides and precursors Organics undergo chemical reactions that involve the formation of secondary particles such as sulfate, nitrate, ammonium and organic compounds.

Emissions of organic species from agricultural activities, biomass burning (firewood, leaves, charcoal vegetable etc.), together with the combustion of petroleum (gasoline and Diesel) are important sources of aerosols secondary. The oxidation of the gaseous precursor formed as a result of the aforementioned activities contributes to increase the final PM fraction or is adsorbed to coarse particles.

danger

The PM generates a significant negative impact on the health of people and the environment.

After direct inhalation of PM, it enters the respiratory system causing allergies, inflammation and a temporary reduction in respiratory capacity. Fine particles (<1 µm) can enter and settle within the respiratory system (bronchi and alveoli) generating serious respiratory diseases, such as chronic asthma, emphysema and lung cancer. lung. In addition, some of the most toxic and carcinogenic compounds, such as Aromatic Compounds (PACs) and polychlorinated biphenyls (PCBs) have been detected in particulate matter atmospheric. The WHO has estimated that approximately 3% of deaths from cardiopulmonary cancer and 5% of lung cancers are attributable to MP worldwide.

The MP also affects the climate on a local and global scale, with impacts on the albedo and cloud nucleation processes. In addition, the organic type PM is considered one of the main responsible for the acidification of rainwater.

predictive models

The physicochemistry of these particles is complex because it involves processes of transformation into based on thermodynamic properties such as vapor pressure, phase diagrams and solubility and reactivity. Therefore, the development of predictive models of critical phenomena of pollution by MP, requires technical knowledge on sampling methods, geographic and climatic variables.