Main indoor air pollutants
Gases
Inorganic gases
Inorganic gaseous air pollutants are a significant group of air contaminants that lack carbon-hydrogen bonds, distinguishing them from organic pollutants.
These gases, including ozone (O3), sulfur dioxide (SO2), nitrogen dioxide (NO2), and carbon monoxide (CO), originate from various sources such as vehicle emissions, industrial processes, and natural occurrences like volcanic eruptions.
Organic gases
Organic gaseous compounds can be categorized based on their boiling points, which directly relate to their volatility - their tendency to evaporate at room temperature. This causes their different behaviour in indoor air. Also, the health effects can vary depending on the specific compound and its volatility.
Very volatile organic compounds
Very volatile organic compounds (VVOCs) are gases at room temperature and very easily evaporate.
Examples:
- Formaldehyde (although some sources classify it as a VOC)
- Methane
- Butane
- Propane
- Freons (e.g., chlorodifluoromethane)
Volatile organic compounds
Volatile organic compounds (VOCs) are a large group of chemicals that easily evaporate at room temperature and are the most commonly referred to group when discussing VOCs in indoor air. VOCs are also mainly gases but they may condense on colder surfaces.
They are found in many common household products and building materials, and they can have a significant impact on indoor air quality (IAQ).
Examples:
- Benzene
- Toluene
- Xylene
- Acetone
- Ethanol
- Isopropanol
- Many components of fragrances and cleaning products
Semi-volatile organic compounds
Semi-volatile organic compounds (SVOCs) have lower volatility than VOCs and tend to exist both in the gas phase and adsorbed onto surfaces or particles (like dust).
Examples:
- Phthalates (plasticizers)
- Polychlorinated biphenyls (PCBs) - mostly phased out but can be found in older buildings
- Polyaromatic hydrocarbons (PAHs)
- Some pesticides
- Flame retardants (PBDEs)
Radon
Radon is a naturally occurring radioactive gas that is colorless, odorless, and tasteless. It is formed from the decay of uranium, which is found in rocks and soil throughout the world.
Radon gas can seep into homes and buildings through cracks and openings in the foundation, floors, and walls. It can also be released from building materials that contain radium.
Indoor air particles
Particulate matter (PM) is a mixture of solid particles and liquid droplets suspended in the air. These particles vary in size, composition, and origin, and their effects on human health depend on these characteristics.
PM is classified by its aerodynamic diameter, which is the size of a unit-density sphere with the same aerodynamic properties as the particle.
Coarse particles (PM10)
Coarse particles are inhalable particles, with diameters that are generally 10 micrometers and smaller.
Fine particles (PM2.5)
Fine particles are inhalable particles, with diameters that are generally 2.5 micrometers and smaller. Due to their small size, they can penetrate deep into the respiratory tract, reaching the lungs.
Ultrafine particles (PM0.1 )
Ultrafine particles (UFP) are a subset of particulate matter with a diameter of less than 0.1 micrometers. Due to their extremely small size, UFP can penetrate deep into the lungs and potentially enter the bloodstream, raising concerns about their health effects.
Biological agents
This category encompasses living organisms and their byproducts that can negatively affect indoor air quality.
Mold and Fungi
These microorganisms thrive in damp or humid indoor environments and can release mycotoxins, which can have carcinogenic, immunotoxic, cytotoxic, and mutagenic effects.
Bacteria
Similar to mold, bacteria can grow in damp conditions and cause health issues.
Viruses
These can be transmitted through the air, especially in poorly ventilated spaces.
Allergens
These substances can trigger the immune system, causing allergic reactions. Common indoor allergens include dust mites, pet dander, and pollen.
Concentration limit values for main air pollutants
| Categorization | Pollutant | Averaging period | Concentration limit value | Reference | |
|---|---|---|---|---|---|
| Organic gases | Benzene | - | no safe level | WHO 2010 [1] | |
| Naphthalene | annual | 10 | μg/m3 | WHO 2010 [1] | |
| Polycyclic aromatic hydrocarbons | no safe level | WHO 2010 [1] | |||
| Tetrachloroethylene | annual | 250 | μg/m3 | WHO 2010 [1] | |
| Trichloroethylene | WHO 2010 [1] | ||||
| Formaldehyde | 30-minute | 100 | μg/m3 | WHO 2010 [1] | |
| Inorganic gases | O3 | 8-hour
peak season |
100
60 |
μg/m3 | WHO 2021 [2] |
| SO2 | 10-minute
24-hour |
500
40 |
μg/m3 | WHO 2021 [2] | |
| NO2 | 1-hour
24-hour annual |
200
25 10 |
μg/m3 | WHO 2021[2] | |
| CO | 15-minute
1-hour 8-hour 24-hour |
100
35 10 4 |
mg/m3 | WHO 2021 [2] | |
| Particulate matter | PM2.5 | 24-hour
annual |
15
5 |
μg/m3 | WHO 2021 [2] |
| PM10 | 24-hour
annual |
45
15 |
μg/m3 | WHO 2021 [2] | |
| Radioactive gases | Radon | ||||