Volatile organic compounds and formaldehyde

VOCs are organic compounds with a boiling point between 50°C and 260°C. In VOC analyses, the results are often in the form of toluene equivalents, which represent the concentration calculated by comparing the compound’s detector response to the detector response of toluene (Fromme et al. 2019).

Total volatile organic compounds (TVOCs) is defined as the sum of the concentrations of all VOCs (identified or non-identified) between n-hexane and n-hexadecane and calculated as toluene equivalents (ISO 16000-6:2011). The normal analytical procedure involves collecting air samples in sorbent tubes, such as Tenax TA, and thermally eluting them with a non-polar gas chromatography column for analysis(ISO 16000-6:2011, Mølhave et al. 1997). TVOC provides an estimation of the composition of the chemicals in indoor air, and is therefore, used as an indicator of the chemical load, contamination sources or insufficient ventilation (Fromme et al.2019). However, it does not account for the potency of the single compounds, or exposure to low levels of VOC mixtures or high concentrations of specific substances. For the European Union (EU), the European Community has created guidelines which stipulate that the maximum concentration of TVOCs must not exceed0.3 mg/m3, and the concentration of individual VOCs must not exceed 10% of the set maximum. The target concentrations of single substances should be set based on toxicology analysis. Substances with a low odour perception threshold and compounds or mixtures with a high probability of sensory effects, odour perception or discomfort (Salthammer 2011, Andersson et al. 1997) need additional assessment. In new or freshly renovated buildings, increased VOC values are accepted for up to 12 months (Fromme et al. 2019).

Formaldehyde (HCHO) is a ubiquitous air contaminant with various adverse effects on humans (Tsai 2019, Salonen et al. 2009, WHO 2010). Airborne formaldehyde can be released from several sources, such as paints, coatings, wall and floor coverings, and furnishing (Rovira et al. 2016). In classrooms, formaldehyde concentrations are found to be very low, or even below detectable limits (Yang et al.2009, Lee and Chang 2000).

The gaseous pollutants detected in school buildings include VOCs and inorganic gases, of which the most commonly detected ones are CO2, carbon monoxide (CO),nitrogen dioxide (NO2), sulphur dioxide (SO2), and ozone (O3). Indoor emission sources, such as indoor building and furniture material, play a major role in VOC exposure (Paciência et al. 2016). In schools, the emission sources include typically used cleaning products and materials for art and craft (Śmiełowska et al. 2017,Mishra et al. 2015). Additionally, occupants’ behaviour and activities, as well as season, affect the indoor VOC concentrations. In a review study by Paciencia et al.(2016), higher mean concentrations of known VOCs were found during the cold season, with the concentrations varying from undetectable to 160 μg/m3. The levels of certain VOCs are sometimes much higher indoors than outdoors. The most common species of VOCs found in school environments are benzene, toluene, ethylbenzene and xylene (Chithra and Nagendra 2018), and among them, toluene is found in the highest concentrations in classrooms (Madureira et al. 2015, Demirel et al.2014, Raysoni et al. 2013, Jovanović et al. 2014).

Source: Camilla Vornanen-Winqvist. 2020. "Indoor air contaminants, symptoms and effects of mechanical ventilation in school buildings"