The size of air particles and their effects on health

Thanks to the work of John Tyndall, the world knows that the air we breathe contains particles. These particles are of different sizes and have different effects on human health. In the era of the COVID-19 pandemic, we may be interested in finding how the viral particles spread in the air, and what could be their effects on human health.  

According to the American Conference of Governmental Industrial Hygienists (ACGIH), The International Organization for Standardization (ISO) and the European Committee for Standardization (CEN), aerosols in the air should be classified following their size and the site in the human body where they deposit. Therefore, these aerosols form three (3) groups: 

1. The inhalable fraction that contains particles with diameters less than 100 microns and that affects the entire respiratory system. These particles can be inhaled by the mouth or the nose. 
2. The thoracic fraction contains all the particles that have a diameter size of less than ten (10) microns and deposit in the pulmonary region and in the alveoli where gas exchanges occur. 
3. The respiratory fraction contains all the particles with size less than four (4) microns and that affects the alveolar region. 

This categorization however is mainly used for sampling purposes and is general in a sense it regroups particles of different sources and variable sizes. Also, the grouping is not exclusive since the thoracic and the respiratory fractions are included in the inhalable fraction. 

Viruses don’t travel alone

Particulate matters (PM) are made of solid or liquid particles suspended in the air, they come in many different sizes and shapes. These particles may include dust, dirt, soot, smoke, or drops of liquid. They are so tiny that they generally can’t be seen by the human eye. The categories depend on the particles size as follow: 

• PM 10: particles with size less than 10 microns
• PM 2.5: particles with size less than 2.5 microns
• PM 1: particles with size less than 1 micron (also known as Ultrafine Particles -UFP). 

The term Volatile Organic Compound (VOC) refers to particles that are emitted as gases in the air, from certain solids or liquids. As with the PM, they can have diverse sizes and origins. 

The coronavirus virion (viral particle) is also a small particle with a diameter size of 0.125 microns on average (0.06-0.14), which makes it even more dangerous. However, this virion is not able to travel alone. It is always contained in suspended particles. In other words, controlling the content of suspended PM and improving the air quality may contribute to a significant reduction of the spread of the disease through suspended particles.  

Sources of the particles in the air

PMs can either be emitted directly from a source, or result from other chemical reactions in the atmosphere. They generally come from fuel combustion such as burning coal, oil, wood and light fuel oil in domestic fires, transportation and industrial processes. UFP can also result from activities such as cooking indoors or road traffic outdoors. 

VOCs have many sources. They can be emitted from paints, paint strippers and other solvents, wood preservatives, aerosol sprays, cleansers and disinfectants, moth repellents and air fresheners, stored fuels and automotive products, hobby supplies, dry-cleaned clothing or pesticides. 

Effects on human health 

When we breathe, our nose and air passages filter the particles and remove those that are bigger than 10 microns in diameter. The smallest particles are more hazardous than the bigger ones, and can travel far and deep in the human body: they can penetrate the lungs and in some cases reach the blood. Some of the common effects known from breathing in these PMs are the irritation of eyes, throat and lungs, trouble breathing and in some cases lung cancers. 

Here's a video that explain air pollution and its effect on the body.

What can we do? 

The first action to take in reducing the negative effects of breathing PM is actually detecting and knowing the quantity of the PM in the air: several options are available including AirQTrack, which allows a live monitoring of different particles in the air indoors. Indeed, knowing and assessing the air  quality allows us to take necessary measures and act appropriately when needed. 

The second action to take when the air quality is not good enough depends on the presence of particles and the means of improving air quality: for instance, an excess of carbon dioxide might require us to open the windows, activate the mechanical ventilation or reduce the number of people in the room. Other solutions include the improvement of the air by organic means (TakeAir). 

"Particles are present in the air we breathe, and it is our responsibility not only to monitor the quality of this air, but also to improve it. Responsible actions will promote good health and will reduce negative effects of the polluted air in our body, which will contribute to the improvement of our life expectancy."

- Confiance Mfuka, PhD