Aerosol Air Fresheners VOCs Impact Indoor Air Quality
Indoor Air Quality and Aerosol Air Fresheners: Navigating VOCs, Propellants, and Valve Design
A 2021 study by Heeley-Hill and Grange from the University of York and Givaudan measured wintertime indoor n-butane levels as high as 4,630 μg/m³, primarily from aerosol propellants. These findings provide formulators with data to assess the impact of aerosol fragrance products on indoor air quality. Effective management of volatile organic compound (VOC) emissions requires strategic consideration of ingredient limits, propellant selection, and delivery systems.
Key Takeaways
- Indoor VOC levels exceeded outdoor levels in 84% of homes in summer and 100% in winter, with aerosol propellants like n-butane and propane among the most abundant compounds.
- Reducing hydrocarbon propellant use would likely have the greatest impact on lowering domestic VOC emissions.
- Formulators must account for VOC contributions from both fragrance concentrate and propellant system.
- Valve selection directly influences spray characteristics, particle size, and VOC release rate.
- Choosing low-VOC propellants and efficient delivery systems can reduce ambient VOC levels.
Propellant Gases Are a Dominant Source of Indoor VOCs
The study analyzed 72-hour air samples from 60 UK homes. N-butane and propane were identified as the most concentrated VOCs indoors, particularly in winter when homes are sealed. N-butane concentrations ranged from 1.5 to 4,630 μg/m³. These gases serve as propellants in aerosol products including air fresheners, deodorants, and cleaners.
When aerosol is sprayed, the compressed or liquefied propellant gas expands to disperse fragrance droplets. In ventilated spaces, these gases dissipate quickly, but in closed rooms they accumulate. The study found that reducing hydrocarbon propellants would more effectively lower total indoor VOC load than focusing solely on fragrance compounds like tridecane or tridecanal.
Limitations in Predicting Indoor Concentrations from Product Use
The study found little correlation between reported product use frequency and measured VOC levels. Households used VOC-containing products like deodorants an average of 2.9 times daily, but this usage data did not predict 72-hour averaged indoor concentrations. Room volume, ventilation rate, and air exchange proved more influential than frequency of use.
For formulators, this means VOC limits must account for worst-case scenarios. A product sprayed in a small, unventilated bathroom creates higher localized concentrations than in a large, open space. Formulation strategies should minimize peak concentrations through propellant-fragrance compatibility to prevent phase separation or inconsistent spray patterns.
Formulation Levers: Propellant Alternatives and Valve Engineering
Two systems require optimization: propellant and valve. Hydrocarbon propellants like n-butane, propane, and isobutane are cost-effective but contribute to VOC load. Alternatives include compressed gases like nitrogen or carbon dioxide (non-VOCs) and hydrofluoroolefins (HFOs) with low VOC potential and global warming impact. Each alternative affects spray characteristics, pressure, and fragrance solubility.
Valve design controls product delivery. A precision-engineered valve releases consistent, fine mist with optimal droplet size for dispersion. Poor valve performance produces large droplets that require more sprays to achieve desired scent, increasing VOC emissions. This mechanical function is as critical as chemical stability of ingredients like triethanolamine.
Actionable Guidance for Fragrance Formulation
Formulators should: (1) Calculate VOC contributions from fragrance oil, solvents, and propellant, ensuring regulatory compliance; (2) Test propellant compatibility to prevent clogging and ensure consistent spray ratios; (3) Select valves engineered for product viscosity and spray pattern; (4) Provide clear usage instructions to prevent over-application.
Conclusion
The University of York study confirms aerosol propellants as major sources of indoor VOCs. Effective fragrance formulation requires optimizing VOC limits, propellant choice, and valve mechanics to balance scent performance with air quality concerns.
Fragrance Studio lets you test materials against aerosol propellant systems and VOC limits directly — no spreadsheet juggling, with data sourced from Fenaroli, IFRA, PubChem and more.