Volatile Organic Compounds

What are VOCs?

VOCs are widely prevalent gases that emanate from specific solids or liquids. They are common in various manufacturing processes, consumer and commercial products (CCPs), and even natural sources such as plants and wood. However, the regulatory definitions of VOCs differ across various global entities.

The U.S. and Canada categorize VOCs as carbon compounds that participate in atmospheric photochemical reactions, albeit with some exceptions.

The United Kingdom and the European Union classify any organic compound with an initial boiling point of 250 C or less at 101.3 kPa as a VOC.

The World Health Organization (WHO) further segments VOCs based on boiling points. This ranges from Very Volatile Organic Compounds (VVOCs: <0 to 50–100 C), VOCs (50–100 C to 240–260 C), to Semi-volatile Organic Compounds (SVOCs: 240–260 C to 380–400 C). It is crucial to underscore that these boiling point variations do not directly correspond with their respective health risks. In certain scenarios, the health risks associated with SVOC emissions might even surpass those of VOCs.

In atmospheric chemistry, Intermediate VOCs (IVOCs) are introduced to bridge the volatility gap between traditional VOCs and SVOCs, while Oxygenated VOCs (OVOCs), composed of carbon, hydrogen and oxygen, are predominantly introduced as emissions from vehicle exhaust and atmospheric interaction.

VOCs are omnipresent pollutants that readily evaporate, compromising air quality. They typically emanate from diverse sources, including but not limited to building materials, cleaning agents, paints, composite wood products, adhesives, sealants, and various CCPs like air fresheners, insecticides, insect repellents and hairsprays. Notably, benzene, often found in glues, paints, furniture wax and various cleaning products, and trichloroethylene, prevalent in substances like adhesives, paint removers, varnishes, lubricants and spot removers, are common VOCs. VOCs may further react with naturally occurring indoor air compounds like ozone to form secondary pollutants including formaldehyde, posing covert risks to IAQ. When inhaled or assimilated into the bloodstream, VOCs can cause irritation or, in extreme cases, lead to significant organ and tissue damage.

Ongoing research into VOCs underscores a growing concern: emerging indoor pollutants such as phthalates and polychlorinated naphthalene (PCN) pose significant health risks. Phthalates, widely utilized as plastic additives, and PCNs, commonly found in electrical wire coatings and lubricants, have been subject to regulatory oversight due to their hazardous profiles. However, the legacy of these substances endures, as VOC emissions from pre-regulation materials can persist for years, potentially compromising indoor air quality in older buildings.

How to improve IAQ with less VOCs?

Regular IAQ assessments

The importance of regular assessments for indoor air quality, specifically for VOCs, is significant. A focused review of the air quality standards from WHO and the two largest global economies, China and the U.S., was undertaken (see Table 1). The review encompassed WHO guidelines, standards from the U.S. Green Building Council and the International WELL Building Institute, as well as regulations from mainland China and Hong Kong. Notably, WHO has not set a specific exposure limit for benzene, in contrast to China's established standard and the more stringent limits set by both LEED and the WELL Building Standard for particular VOCs.

Alternatively, Hong Kong’s guideline, devoid of specific VOC limits, imposes strict control over total VOCs (tVOCs) with a limit of 200 micrograms per cubic meter of air over an eight-hour period — a standard more rigorous than those of both LEED and mainland China. This tVOCs focus likely stems from the technical complexities inherent in measuring specific VOCs, which require complex techniques like chromatography-mass spectrometry (GC-MS). With VOC level being typically low, advanced methods including quadrupole time-of-flight (QToF) mass spectrometry and dynamic headspace are employed to enhance sensitivity. Additionally, the application of well-ready semiconductor or photochemical sensors in handheld tVOC detectors facilitates quick, albeit preliminary, assessments against recognized benchmarks to gauge indoor VOC presence.

Pollutants reduction at source

Considering the complexities of measuring specific VOC levels, a preventive approach is more proficient and effective for VOC management. This involves the mindful selection of building materials, finishes, coatings and sealants with low VOC contents. When enhancing cleaning protocols, particularly during pandemic outbreaks or flu season, it is critical to consider the potential VOC emissions from various cleaning products including hand and general-purpose cleaners, tile and glass cleaners, disinfectants, sanitizers and deodorizers. Cleaning service providers and maintenance or retrofitting contractors must be trained to select non-toxic, eco-friendly options, favoring water-based or low-VOC products over solvent-based products for the course of work. Mindful material selection is also pivotal in VOC management; composite materials generally emit more VOCs than solid wood, although solid wood can also harbor VOCs, typically because of treatment processes. Modular Integration Constructions (MiC) and similar off-site installation can reduce the use of site-applied paints, adhesives and sealants, allowing for the off-gassing of VOCs prior to indoor installation.

Certain facilities, such as hair salons, auto repair shops, cosmetics stores and bath and body shops, commonly use high-VOC products. Even with the California Air Resources Board’s updated regulations, effective Aug. 1, 2022, which cap the VOC content of hair products like finishing sprays at 50 percent by weight and personal fragrances at up to 70 percent by weight, these environments necessitate strategic planning to mitigate VOC overexposure risks for both staff and customers. Facilities such as restaurants and kitchens, where cooking methods like frying, grilling and stir-frying are common, also generate substantial VOC emissions and require dedicated IAQ management.

Although low-VOC and zero-VOC products are marketed for their environmental advantages, German research suggests they may still release significant levels of harmful substances. Facility managers are advised to obtain and review supplier test reports, ensuring full understanding of product emissions. This includes scrutinizing the definitions of VOCs used, as some harmful VOCs might be omitted from standard declarations.

Engineering-based interventions for VOC management

Upkeep of air-conditioning and ventilation systems through regular inspections and maintenance, such as filter replacements, coil cleanings and sensor calibrations, is integral to maintaining healthy indoor environment and preventing the build-up of VOCs within facilities. During activities like cleaning, retrofitting or repair, which may involve the use of VOC-rich substances like paints or adhesives, ventilation should be increased. Humidity control is also key in VOC management. Research indicates that keeping relative humidity below 60 percent can reduce the indoor concentration of specific VOCs, such as toluene and xylenes, due to decreased solubility on indoor materials. Evaluating the placement of air intakes is also vital to prevent the infiltration of outdoor VOCs from nearby vehicle exhaust or industrial emissions.

Having VOC removal devices, like air cleaners within facilities, is crucial. Standard filters in central HVAC systems primarily capture particulates and are ineffective against gaseous pollutants like VOCs. Even advanced filters like high-efficiency particulate air (HEPA) filters or ultra-low particulate air (ULPA) filters cannot remove VOCs, given their gaseous nature. Air cleaners equipped with activated carbon or photocatalytic reactors can help eliminate VOCs from indoor air. This approach is particularly useful during cold or severe weather when buildings are tightly sealed, restricting fresh air intake.

While ozone generators are often marketed as air purifiers, these units generate ozone, a lung irritant that can be harmful to indoor occupants, especially those with respiratory conditions. Furthermore, at concentrations that do not exceed public health standards, ozone may not remove indoor air contaminants. Additionally, ozone can react with VOCs to form secondary pollutants, which can further degrade IAQ and potentially pose additional health risks. As such, ozone generators are not recommended for gaseous pollutant removal.

While particulate matter often captures the spotlight in IAQ, VOCs warrant equal attention. Their ubiquitous presence in everyday substances and ability to infiltrate our spaces underscore the need for heightened vigilance and concerted efforts in mitigating their impact. While monitoring and controlling specific VOCs present technical challenges, a preventive approach – undertaking regular IAQ assessments and applying engineering-based interventions – can significantly enhance indoor air environments. It is also crucial to understand that products labeled low-VOC or zero-VOC are not standardized and may still contain VOCs. Thus, making informed decisions based on a thorough understanding of product content is vital. As we continue to refine our strategies in the battle against unseen air quality threats, let us keep shining a spotlight on VOCs – a significant parameter of IAQ.

Table 1. Limits for selected VOC*

	Carcinogenicity defined by International Agency for Research on Cancer (IARC)	China’s Standard GB/T 18883-2022	EPD Guideline, Hong Kong a	LEED v4.1 Building Design and Construction b	WELL Building Standard v2, Q4 2023, Feature A01	WHO Guidelines for Indoor Air Quality (2010): selected pollutants
Benzene	Group 1	0.03mg/m3 (1hr)	n.a.	3µg/m3	10µg/m3 or 3µg/m3 d	No safe level of exposure can be recommended
Formaldehyde	Group 1	0.08mg/m3 (1hr)	30µg/m3 (8hr) or 70µg/m3 (30min)	20µg/m3	50µg/m3 or 9µg/m3 d	0.1mg/m3 (30min)
Benzo[a]pyrene (BaP) (PANs’ representative)	Group 1	1.0 mg/m3 (24hr)	n.a.	n.a.	n.a.	n.a.
Acetaldehyde	Group 2B	n.a.	n.a.	140µg/m3	140µg/m3 d	n.a.
Dichlorobenzene (1,4-)	Group 2B	n.a.	n.a.	800µg/m3	n.a.	n.a.
Hexane	n.a.	n.a.	n.a.	7000µg/m3	n.a.	n.a.
Naphthalene	Group 2B	n.a.	n.a.	9µg/m3	9µg/m3 d	0.01mg/m3 (annual average)
Phenol	Group 3	n.a.	n.a.	200µg/m3	n.a.	n.a.
Styrene	Group 2A	n.a.	n.a.	900µg/m3	n.a.	n.a.
Tetrachloroethylene	Group 2A	0.12mg/m3 (8hr)	n.a.	35µg/m3	n.a.	0.25mg/m3 (annual average)
Trichloroethylene	Group 1	0.006mg/m3 (8hr)	n.a.	n.a.	n.a.	n.a.
Toluene	Group 3	0.20mg/m3 (1hr)	n.a.	300µg/m3	300µg/m3	n.a.
Vinyl acetate	Group 2B	n.a.	n.a.	200µg/m3	n.a.	n.a.
Xylene	Group 3	0.20mg/m3 (1hr)	n.a.	700µg/m3	n.a.	n.a.
Total VOCs	n.a.	0.60mg/m3 (8hr)	200µg/m3 (8hr)	500µg/m3 c	500µg/m3	n.a.

 

*The table is not exhaustive. Refer to the respective publications for exact details.

^a Excellent Class of IAQ objectives stipulated in “A Guide on Indoor Air Quality Certification Scheme for Offices and Public Places” (2019).

^b This EQ credit also applies to LEED v4.1 Interior Design and Construction.

^c If TVOC levels exceed 500 µg/m3, compare individual VOC concentrations from GC/MS analysis with health-based standards set by relevant authorities. Remediate any detected issues and perform re-testing if needed.

^d Feature 05 Optimization Enhanced Air Quality