Volatile Organic Compounds (VOCs): What are they, common sources, and how to reduce their impact?

Introduction

Organic compounds, also known as organic molecules, are chemical substances of biological origin, due to the presence of carbon as the central element. These compounds are mainly composed of carbon and hydrogen, with the frequent presence of other non-metallic elements such as nitrogen, oxygen, phosphorus and sulfur, joined by covalent bonds that guarantee stability and structural differences.

Among the different organic compounds are volatile organic compounds, in a gaseous state at ambient temperature. This group includes a series of chemical substances present in products, such as paints, solvents and fuels, which significantly affect air quality. The study and control of these compounds, besides being relevant from a chemical perspective, is necessary due to their implications on human health and the environment.

What are Volatile Organic Compounds (VOCs)?

Volatile organic compounds (VOCs) are a category of hydrocarbons characterized by their high volatility at room temperature, defined by a vapor pressure equal to or greater than 0.01 kPa at 20 °C¹. These compounds, with carbon chains typically smaller than twelve atoms, may include other elements such as oxygen, nitrogen, fluorine, chlorine, bromine or sulfur in their molecular structure. VOCs originate from both natural sources (biogenic) and human activities (anthropogenic), including solvent evaporation, fossil fuel combustion and the use of industrial products such as paints, adhesives and plastics.

From an environmental point of view, VOCs are considered pollutants due to their active role in atmospheric chemical reactions. When combined with nitrogen oxides in the presence of sunlight, they contribute to the formation of tropospheric ozone and photochemical smog, affecting both air quality and climate change by reinforcing the greenhouse effect. Their health impacts are significant, including eye irritation, respiratory irritation and allergic reactions, as well as damage to internal organs such as the liver and kidneys. Additionally, in the environment they can interfere with biological processes such as photosynthesis.

Characteristics of Volatile Organic Compounds

Classification according to origin

• Natural sources: Biogenics are molecules naturally emitted by living organisms, mainly plants, trees and other vegetation. These emissions result from metabolic processes such as photosynthesis and respiration. Notable examples include compounds such as terpene, limonene and pinene, which contribute to the natural fragrance of forests and the ecological interaction between organisms.
• Anthropogenic sources: These are emissions released into the environment as a result of human activities. These emissions derive from industrial processes, the use of fossil fuels, the production and disposal of chemicals, and the use of materials such as paints, solvents and adhesives. Representative examples include benzene, formaldehyde, toluene and xylene, compounds that pose risks to both human health and the environmental balance.

Classification according to hazard

• Extremely hazardous components: These represent an extreme danger to human health due to their high toxicity and the long-term effects they can cause. These include benzene, vinyl chloride, 1,2-dichloroethane and sulfur².
• Class A compounds: These are compounds that, while not necessarily as lethal as extremely hazardous compounds, have a high potential for environmental damage. Their impact on ecosystems and public health can be significant, especially when released in large quantities.
• Class B components: They have a lower impact on human health and the environment compared to class A and extremely hazardous. Although their hazardousness is not as high, they are still volatile substances that require control to avoid long-term effects.

Common sources of VOC emissions

Domestic sources

Everyday products represent a significant source of volatile organic compounds. These chemicals are released into the air during use, storage or combustion and can contribute to both indoor air pollution and the development of health problems in household occupants³.

The main domestic sources of emissions include:

• Paints and finishing products: Paints, furniture polishes and coatings release organic solvents into the environment.
• Cleaning products: Soaps, detergents and disinfectants contain volatile compounds that can be dispersed in enclosed spaces.
• Solvents and thinners: Items such as acetone-based nail polish removers and paint thinners are prominent emitters of VOCs.
• Aerosols: Air fresheners and aerosol cleaners contain volatile propellants and fragrances that impact indoor air quality.
• Domestic combustion: Smoke from stoves, candles and cigarettes releases volatile hydrocarbons and other toxins.

Industrial and agricultural sources

In the industrial sector, factories and plants involved in the production of plastics, petrochemicals and other large-scale products emit volatile organic compounds through processes such as combustion, solvent evaporation and the handling of volatile materials. In addition, waste management and recycling facilities, especially those using incineration, release large amounts of these compounds into the environment due to the high volatility generated by heat. Proximity to these sources can increase human exposure to harmful levels of VOCs, affecting environmental health and safety.

In agriculture, VOC emissions are related to intensive livestock farming and the use of fertilizers and pesticides. Livestock farms, especially those dedicated to raising cows, generate methane, a potent greenhouse VOC, through digestive processes and the decomposition of manure³ . The application of agricultural chemicals also contributes to the release of toxic vapors that can be dispersed over long distances.

VOCs and transportation

Transportation is one of the main anthropogenic sources of volatile organic compound emissions, contributing significantly to environmental pollution. These compounds, emitted by fuel combustion, vehicle refueling and the use of materials inside vehicles, play a critical role in the formation of tropospheric ozone and photochemical smog, factors that negatively impact air quality and human health.

In addition, inside vehicles, interior materials such as adhesives, paints and cleaning products, together with factors such as temperature and ventilation, generate VOCs that affect drivers and passengers. These internal emissions are in addition to external emissions from exhaust gases and air pollutants.

How to reduce the environmental impact of VOCs

Home and office control methods

Control of volatile organic compounds in indoor environments, such as homes and offices, is necessary to improve air quality and minimize the health risks associated with exposure to these pollutants. The best strategy to reduce the impact of VOCs is to act directly on their sources, using both preventive and remedial approaches⁴.

1) Selection of low VOC materials and products

One of the most effective methods of limiting VOC emissions is to choose building and decorative products that are low in VOCs. For example, paints, varnishes and adhesives specifically labeled “low VOC” should be selected. These products release fewer volatile compounds during application and subsequent curing, significantly reducing the concentration of VOCs in indoor air. In addition, products that release volatile chemicals continuously, such as air fresheners, scented candles or incense, should be avoided.

2) Proper handling of chemicals and new materials

When new materials are incorporated into a closed environment, it is essential to allow them to release their volatile gases before use. In the case of furniture, carpets or building materials, it is advisable to store them in a ventilated place for a few weeks before bringing them indoors. If this is not feasible, ventilation should be increased in the enclosed space by opening windows and doors, which favors the dispersion of the released gases.

For products such as paints, cleaners and solvents, it is recommended that only the necessary amount be purchased to avoid prolonged storage in the home. These products should be stored in a ventilated area, such as an outdoor shed, and in tightly closed containers to minimize emissions.

3) Adequate ventilation and control of emission sources

Ventilation is a key component in reducing the buildup of volatile organic compounds in interior spaces. Ensuring the circulation of a constant flow of fresh air is vital, especially after the installation of new materials such as carpeting or furniture. During the installation of these materials, it is important to keep windows open and use fans to increase air circulation, which promotes the removal of volatile compounds.

It is important to follow the instructions for household chemicals, especially when they are to be used in well-ventilated areas. In such cases, the tasks should be carried out outdoors or in areas with good air extraction.

4) Safe disposal and disposal of products with VOCs

When it is desired to dispose of products such as solvents, paints or cleaning products containing VOCs, this should be done in a safe manner and not through household waste. Proper disposal of these chemicals should be deposited in specialized centers, following local recycling and disposal regulations, which prevents contamination, and protects people who may be exposed during the handling of these materials.

VOC reduction technologies

There are several methodologies that allow the capture, degradation or transformation of these compounds into less harmful substances⁵. For example:

1) Oxidation technologies

Thermal and catalytic oxidation are highly effective methods for the removal of VOCs by converting them into carbon dioxide (CO₂) and water (H₂O) through controlled combustion processes.

• Thermal oxidation: This is carried out at temperatures above 750 °C, where VOCs are completely destroyed. Regenerative systems, which use heat transfer beds, achieve thermal efficiencies above 90%. On the other hand, recuperative systems incorporate heat exchangers that optimize the energy used in combustion.
• Catalytic oxidation: It uses a porous catalytic material to accelerate the oxidation of exhaust gases at lower temperatures (>300 °C). This method allows flameless combustion, reducing energy consumption and improving process efficiency.

2) Adsorption

It is a process in which exhaust gas molecules adhere to the surface of a solid material, activated carbon being the most commonly used adsorbent. This method is highly effective in capturing VOCs at low temperatures, although its efficiency depends on the saturation capacity of the adsorbent material.

3) Absorption

It is based on diffusion mass transfer, where soluble gaseous components are separated from the gas stream by dissolving in a liquid. This technique is effective in the removal of soluble VOCs and is commonly applied in industrial processes with emissions of highly reactive compounds.

4) Biofiltration

It is a biological technique in which microorganisms degrade VOCs into less harmful compounds. This method is an economical and sustainable alternative, ideal for the remediation of gaseous emissions in industrial environments. For its correct operation, a pretreatment of the exhaust gas is required to ensure optimal conditions for the microorganisms involved in biodegradation.

5) Condensation

Condensation allows the recovery of organic compounds in a liquid state after cooling the exhaust gases. To achieve this, it is necessary to reduce the temperature or increase the vapor pressure until the saturation point of the VOCs is reached. This method is particularly useful when seeking to recover and reuse organic compounds in industrial processes.

Each of these technologies has specific advantages depending on the type of VOC emitted, the concentration of the pollutants and the process conditions. The combination of these methods can maximize emission reduction efficiency, contributing significantly to mitigating environmental impact and improving air quality.

Conclusions

The control of volatile organic compounds is essential to mitigate the risks associated with their presence in the air, both for human health and the environment. These compounds, from various natural and anthropogenic sources, are responsible for air pollution and contribute to the formation of tropospheric ozone and smog, which aggravates climate change and affects air quality.

The role of governments, businesses and individuals is also key to a transition to more sustainable practices. Governments must create and implement policies that encourage emissions reductions, while businesses have a responsibility to adopt clean and sustainable technologies. For their part, individuals, by making conscious decisions about their transportation and consumption choices, contribute to reducing pollution and promote positive change in society.

References

1. https://www.miteco.gob.es/es/calidad-y-evaluacion-ambiental/temas/atmosfera-y-calidad-del-aire/emisiones/act-emis/compuestos_organicos_volatiles.html
2. https://es.wikipedia.org/wiki/Compuestos_org%C3%A1nicos_vol%C3%A1tiles
3. https://foobot.io/guides/what-are-the-sources-of-volatile-organic-compounds.php
4. https://www.healthlinkbc.ca/healthlinkbc-files/indoor-air-quality-volatile-organic-compounds-vocs
5. https://www.genano.com/hubfs/How-to%20reduce%20VOC-emissions.pdf?hsLang=es