According to ATMO France, the French federation of AASQAs (accredited associations for air quality monitoring), around 15,000 litres of air pass through our lungs every day. Therefore, it comes as no surprise that people are interested in the potential pollutants in the air. Although outdoor pollution due to industrial, agricultural, heating and transport activities is a major public health concern, the indoor air we breathe daily is also important.
The OQAI (French monitoring centre for indoor air quality) estimates that between our home, workplace, school and other enclosed spaces, we spend more than 90% of our time inside and that indoor air is up to five times more polluted than outdoor air. This is why it is crucial to examine air quality in these living spaces. What is our indoor air status, and which pollutants likely to degrade the air we breathe?
What Is the Difference Between Primary and Secondary Pollutants?
A pollutant is any substance that is likely to be harmful in an environment, including when it is present in quantities below the harm threshold. Some pollutants are introduced by human activities, while others already exist naturally but their quantity is increased by these activities. There are two major families of atmospheric pollutants: primary and secondary pollutants.
• Primary pollutants
Coming directly from pollution sources, these substances are found in the air after being emitted by road traffic, industrial and agricultural activities, etc. They include nitrogen oxides (NOx), primarily emitted by vehicles, and sulphur dioxide (SO2), emitted by some industries and the use of sulphurous fossil fuels. Among the primary pollutants, we also find volatile organic compounds, emitted by vehicles and various industrial processes, as well as particles and hydrocarbons, produced by the combustion of fuel oil or coal.
• Secondary pollutants
These are not emitted by a specific source but are produced by the chemical reaction of various primary pollutants in the air. This is the case, for example, for ozone, born from the reaction of oxygen coming into contact with hydrocarbons and nitrogen oxides interacting with the sun’s UV rays. The same phenomenon exists with nitrogen dioxide, formed by the reaction of nitrogen monoxide with the oxygen naturally present in the air. Some pollutants are both primary and secondary, like nitrogen dioxide, which is also released by thermal power stations and internal combustion engines.
Pollutants Break Down into Several Families:
What Are Volatile Organic Compounds (VOCs)?
Volatile organic compounds (VOCs) mainly come from exhaust gases, even if some are naturally emitted by vegetation. They are used in many everyday products (glue, paint, coatings, solvents…), which explains why we find them inside our homes.
They can be divided into three categories:
– Polycyclic aromatic hydrocarbons (PAHs)
– Monocyclic aromatic hydrocarbons (MAHs, also called BTEX): benzene, toluene, ethylbenzene, ortho-xylene, meta-xylene and paraxylene
– Aldehydes like formaldehyde
The health effects of VOCs vary. Some VOCs are totally harmless to humans in their natural concentration (for example, ethanol). Others present risks, depending on the pollutant involved, which can range from a simple respiratory irritation to a carcinogenic risk (especially benzene and formaldehyde).
When pollutants are potential to be unsafe, they are subject to strict regulation or prohibited. New compulsory labelling identifies reduced emission products. The European Directive 2008/50/CE of 21 May 2008 sets the average annual standard for benzene at 5 µg/m3. French regulations set its quality objective at 2 µg/m3. The directive has also set exposure limit values in work environments for formaldehyde. These guide values have allowed the emissions of these pollutants to be reduced, making their presence in dangerous quantities very rare.
What About PM (Particulate Matter)?
Also called suspended particles, these are all particles (solid or aerosols) carried by water or air.
Some are visible to the naked eye (especially dust or fumes). However, these pollutants are mostly measured in micrometres and thus cannot be seen. Released by industrial and domestic activities, through heating and road traffic, the wind carries them and allows them to travel freely.
Their small size allows them to enter into the respiratory tract, even into the alveoli for the smallest among them, which can cause mild to serious irritation. Some particles have carcinogenic properties. For this reason, the authorities do not recommend exceeding 30 µg/m3 annually, with a limit value of 50 µg/m3 per day over a maximum of 35 days annually.
The Case of CO2 (Carbon Dioxide)
The CO2 that we find indoors comes from outside (industrial activities, transport, etc.), and especially from human presence because CO2 is naturally released when we breathe. Therefore, the CO2 concentration in a confined space continuously increases.
When the level of CO2 is too high (over 1000 ppm=mg/kg), the air quality declines and individuals can experience decreased concentration, drowsiness and headaches. The ANSES (French Agency for Food, Environmental and Occupational Health & Safety) also reports that an experimental study suggests that CO2 affects psychomotor performance (decision-making, problem solving).
Therefore, appropriate regulation exists in places with a sensitive public, and especially in educational institutions. CO2 is notably used to assess the quality of indoor air in many countries, including France. The French Decree No. 2015-1000 of 17 August 2015 thus makes the monitoring of indoor air quality (IAQ) mandatory, by means of a pollutant measurement campaign (including CO2) and a self-assessment allowing an action plan to be established.
What Specific Pollutants Are Found in the Air?
Pollutants present in the air include:
Formed by the chemical reaction of nitrogen oxides and hydrocarbons under the sun’s UV rays, ozone is a strong irritant to the eyes and respiratory tract.
• Carbon monoxide (CO)
A combustion residue, CO primarily comes from exhaust gases, and also from domestic combustion. A poorly maintained boiler can release carbon monoxide and cause indoor poisoning.
• Nitrogen oxides (NOx)
Nitrogen monoxide (NO) and nitrogen dioxide (NO2) are both combustion residues, and although the former is only found in small amounts in the air, the latter can irritate the respiratory tract.
• Sulphur dioxide (SO2)
Discharged into the air by industrial activities, and domestic heating, this gaseous pollutant is irritating to mucous membranes and the respiratory tract.
• Heavy metals
Although the lead emitted by transport saw its concentration decrease with the phase-out of leaded petrol in 2000, it can still be found in the air, from industrial activities and diverse combustions, just like mercury, arsenic, nickel, and cadmium. Present in small amounts, these toxic pollutants can still accumulate in the body in the long term.
It is clear that the air that we breathe, while largely composed of nitrogen and oxygen, can contain many other substances, harmless or harmful to our health. To preserve it, particular attention should be paid to indoor air quality, where CO2 proves to be a good indicator. By carefully monitoring the pollutant content of our air, we can take action to improve it. For example, if the level of carbon dioxide in a room is too high, ventilating the room renews the air and improves the indoor air quality by diluting other pollutants that may be present.