Air Quality in Cars: Pollutants and Challenges

Written by Iñigo Mateo, Industrial Engineer  Grupo Antolin Innovation Department   Vehicle interior air quality has been a topic of interest since the late 1970s when concern over the effect of volatile and semi-volatile organic compounds (VOCs and SVOCs) on the indoor environment began to be replicated in the automotive industry. VOCs are carbon-based gases that can evaporate from certain materials into the air at room temperature. VOCs are ubiquitous and are both naturally occurring (aromatic flowers) and synthetic (paint thinner). All components of a modern vehicle’s interior (except for metals, glass, and ceramics) emit varying levels of VOCs. Some compound and source examples are shown below:

Material	VOC Source	Example Compounds
Polymers (Plastic & Rubbers)	Unreacted monomers	Styrene in ABS, Formaldehyde in PU
	Volatile oligomers	C9-C15 hydrocarbons from PU
	Plasticizer	Phthalates in vinyl
	Antioxidants	Butylated Hydroxytoluene
	Processing chemicals	Siloxanes from mold release
Foam	Catalysts	Triethylenediamine
	Flame retardants	Tris Phosphates
Upholstery	Processing solvents	Dimethylformamide
Adhesive	Acrylic resins	Acrylic acid esters
Carpet	Unreacted monomer	Caprolactam
Coatings	Solvents	Toluene, Xylene

Figure 1: Some potential VOC sources and their compounds Exposure to VOCs can cause discomfort and detrimental health effects such as eye, nose, and throat irritation, headaches and nausea, damage to the liver, kidneys and central nervous system, and in extreme cases, cancer. VOC concentrations have been shown to be at higher levels in automobiles than building interiors and much higher than outdoor concentrations. The off-gassing of VOCs is increased by heat, a common factor found in automobile cabins, making the automotive interior environment one of the highest in VOC concentrations that a person is exposed to in their typical day. Some orientate values of the concentration of various VOCs are shown below:

Compound	Limit Level (mg/m3)
Benzene	≤ 0.05
Toluene	≤ 1.00
Xylenes	≤ 1.00
Ethylbenzene	≤ 1.00
Styrene	≤ 0.26
Formaldehyde	≤ 0.10
Acetaldehyde	≤ 0.20
Acrolein	≤ 0.50

Figure 2: Proposed limit levels from 2017 on

In addition, and intimately related to VOCs, lays the odor problem. Most odors, both good and bad, are the result of VOCs such as formaldehyde, styrene, and xylenes. In the US, for instance,  "new car smell" is a beloved scent. People even try to make their cars smell new with after-market cleaning products. But in China, customers find the same odor repulsive. As the Chinese auto market grows, car makers are looking for a way to make the aroma of their new vehicles more amenable to Chinese tastes.

Last but not least, the intensive use of the car that new ways of mobility advance set the need for means of cleaning the anthropogenic odors and emissions such us high CO2 concentration (due to the breathing process), tobacco smell… Proprietary vehicles lay idle up to 97% of their lifespan and are used by 1.9 people a day on average. With this new paradigm, cars are going to be used by 4 people each day, diminishing their unused times and increasing the importance of the interior air quality perception.

To summarize, pollutant levels are often higher inside, even up to 15x worse than just a few meters away, because cars take in emissions from surrounding vehicles and from its own interior and recirculate them. As environmental concerns increase, and new challenges appear, the need for newer and more efficient air quality management systems is profoundly highlighted.

If you can contribute with a solution to improve air quality in vehicle interiors, help us with the Vehicle Interior Air Quality Management Challenge. Join our community of engineers

Bibliography: 

               

1. B. Xu, X. Chen and J. Xiong, Air quality inside motor vehicles’ cabins: A review, Indoor and Built Environment, 2016, published online.
2. J.D. Power and Associates, China Initial Quality Study, 2016, ‘Unpleasant odour’ was the cause of 16.0 reported problems per 100 new vehicles in the first 90 days after purchase, well above the next most common complaint, ‘Excessive road noise’, with a rating of 5.9.
3. Markes International website
4. GB/T 27630, Guideline for air quality assessment of passenger car, Chinese Ministry of Environmental Protection, 2011.