The air we breathe every day is not just a mixture of gases; it also contains suspended solids and/or liquids. The aerodynamic diameter of these particles determines how far they can penetrate our respiratory system. Compared to outdoors, indoors it is much easier to inhale respiratory particles that can carry viruses and bacteria. This article describes the sources, sizes and types of airborne particles.

Pollutants and respiratory particles

The average person inhales approximately 12,000 liters of air per day, equivalent to the volume of a 12 m² swimming pool that is one meter deep. However, this same person typically drinks only 2 to 3 liters of water per day.

Air inhaled and water ingested by an average adult daily

The air we breathe is composed mainly of nitrogen and oxygen and, although in smaller percentages, also of water vapour (humidity) and other gases, such as argon, carbon dioxide and methane. In addition to these gases, the air also contains solid and/or liquid substances that, together, form a mixture called atmospheric aerosols.

Typical air composition

The solid and liquid substances we inhale can include particles that have negative effects on humans and ecosystems and therefore need to be monitored and managed to ensure the correct indoor and outdoor air quality.

To analyze the impacts of these particles, we can classify them into two broad categories:

• Particulate pollutants , which include airborne particulate matter;
• Respiratory particles , generated by the breathing of living beings.

Pollutant particles: particulate matter carried by the air

The term "airborne particulate matter" refers to all atmospheric particles, solid and liquid, that are suspended in the air. The concentration of these particles [μg/m³] depends on the proximity of the air sample analyzed to the source.

Natural phenomena such as volcanic eruptions, forest fires and aerosols from seawater have always released particles into the atmosphere. However, since the Industrial Revolution, human activities such as car traffic, thermal power plants and building heating systems have contributed significantly to the generation of airborne particles.

Given the nature of the different sources, the composition of particulate matter normally varies (heavy metals, organic carbon, polycyclic aromatic hydrocarbons, dioxins, etc.).

The size of a particle determines how long it remains suspended in the air and, if inhaled by a human, where it will settle in the respiratory tract.

The classification based on particle size is as follows:

• Coarse particulate matter : particles with a diameter greater than 10 μm. They are generally retained in the upper part of the respiratory system (nose, larynx);
• PM10 : fine particles with a diameter of up to 10 μm, which can reach the trachea;
• PM2.5 : fine particles with a diameter of up to 2.5 μm, which can penetrate deep into the lungs;
• PM0.1 : ultrafine particles with a diameter of less than 0.1 μm, which can enter the bloodstream through the pulmonary alveoli and spread to different organs in the body.

Respiratory system and aerosol penetration

The generation of airborne particles with a diameter of about 10 μm due to human activity is mainly due to agricultural soil preparation, brake and tire wear, demolition activities, and industrial processes. Smaller particles are generated by combustion processes, such as internal combustion engines, fossil fuel-fired domestic heating systems, and thermal power plants.

Respiratory particles: droplets and aerosols

Respiratory particles generated by humans through activities such as talking, coughing and sneezing include bacteria, viruses and other microorganisms. In indoor environments, these particles can remain suspended in the air for long periods and be inhaled by occupants, posing potential health risks.

ISH Frankfurt Event

We will explore these topics further during ISH in Frankfurt am Main from 17 to 21 March.
CAREL will be present at stand A61, hall 8.

Visit ish.carel.com .