Relating concentrations of indoor volatile organic compounds to occupant use of solvent-containing products

The air quality of indoor environments has increased in significance over the last few decades, particularly as contemporary estimates suggest that, on average, people spend 90% of their time indoors. This creates a growing requirement to understand the chemical composition of indoor atmospheres, and what factors influence absolute concentrations.  

 

Whole-air canister sampling techniques were used to collect three-day integrated air samples in a cohort of UK homes (n = 60). Each household was sampled three times in winter and three times in summer, plus a further three households were randomly selected each week to also collect an outdoor air sample. Sampling was performed over nine-week periods - between February and April 2019 and July and September 2019. Samples were subject to chemical analysis using a combination of GC-FID and GC-TOF-MS, allowing quantification of VOCs over the range C2 – C12, including nonmethane hydrocarbons, OVOCs, monoterpenes, siloxanes and halocarbons. A digitised survey (completed on iPad) was completed by each household, containing questions regarding property information, residence occupancy and demographics, and a daily log of solvent-containing product usage (including cosmetics and personal care, cleaning, decorative and hobby, smoking, fires, candles, and insecticides). Product usage was determined by how often residents recorded a given product category during the three-day sampling period.

 

Highest concentrations were seen in winter, with n-butane being the most abundant VOC (median value = 61.6 ppb), whilst tetrachloroethylene was the lowest concentration species quantified (median = <0.1 ppb) in this study. In terms of absolute concentration, VOCs derived from aerosol propellants were most significant, plus ethanol and acetone: general purpose solvents from many different product types. Median concentrations for terpenoids ranged from 0.17 ppb p-cymene to 0.65 ppb limonene.  A positive correlation existed internally between different terpenoid species and between alkene species. However, more generally, most individual VOCs did not correlate with each other, highlighting the wide range of uncorrelated sources that contribute to individual concentrations.

 

With the exception of aerosol usage, and n and i butane, indoor ambient VOC concentrations had no statistically significant relationship with product usage frequency, indicating that other factors, such as ventilation rates, VOCs released per dose, variability in product emissions, and other behavioural aspects were potentially more significant influencing factors. This highlights the great challenges in attempting to model indoor exposure to VOCs at a population scale, since it is not readily predictable based on behavioural use of solvents.