Real-Driving Measurement of Vehicle Interior Air Quality and Cabin Air Filtering Performance by Using Low-Cost Sensors

Vehicle interior air quality is usually determined by the levels of in-cabin air pollutants, such as particulate matter (PM), gaseous air pollution (volatile organic compounds [VOCs], oxides of nitrogen [NOx], and carbon monoxide [CO]), and carbon dioxide [CO₂], which reflect the freshness of indoor air. Nowadays, cabin air filters play a key role in preventing outdoor air pollutants transporting inside vehicles; hence, in-cabin air quality can be strongly associated with the filtration performance of cabin air cleaning solutions. However, challenges are existing in a standard method for assessing the performance of a cabin air filter in real-life driving conditions. This study is to develop a low-cost mobile test method for monitoring in-vehicle PM and CO₂ and evaluating the performances of cabin air filters while driving the vehicles. The results reveal that certain boundary conditions are important to have a proper method for evaluating the particle removal efficiency. For example, recirculation ventilation can lead to high PM_2.5 removal efficiency regardless of the status and performance of a cabin air filter, and the remarkable increase in CO₂ in a short time is an obvious indicator of the activation of recirculation. Fresh air ventilation is effective in maintaining the in-cabin freshness without the built-up of interior CO₂; however, drivers can be exposed to a high level of PM_2.5 concentrations with cabin air filters of poor performance. For the vehicles involved in this study, the average PM_2.5 removal efficiencies were about 17-50% under fresh air with existing installed cabin air filters (more than 3 months since installed). With a brand-new filter (original cabin air filter and CabinAir Nordzone™ filter), the vehicle could filter out about 80-86% of outdoor PM_2.5. The application of ionization technology together with the Nordzone™ filter was proven to further enhance the PM_2.5 removal efficiency by up to 97%. Future work would be of great interest to investigate the aging performance of those optimized cabin air filters and the contribution of ionization, as a promising technology to improve the performance of cabin air filters, on those aged filters in real-driving environments.