A survey on the Effect of Ventilation on Air Quality in Vehicle Cabin

Recirculation of air within a vehicle is an excellent approach to limit particle pollution and enhance air conditioner cooling efficiency. Nevertheless, the prolonged use of recirculation air within a vehicle might create high carbon dioxide (CO2) levels due to human exhalation and the lack of fresh air. However, using outside air (OSA) mode exposes occupants to roadway contaminants since outside air enters into the vehicle cabin. The occupants' comfort level can be influenced by the quality of air in the vehicle cabin. A major source of exposure to multiple air contaminants has been established in-cabin microenvironments, such as particulate matter (PM), the total volatile organic compound (TVOC) and carbon dioxide (CO2) concentration [1][2][3]. Hence, increased levels of air quality can cause a health risk. This is already one of road safety's most serious concerns. Although the adverse effects of outdoor pollutants have been given significant attention, there has been a dearth of understanding on the impact on the car occupants from indoor air pollution and quality. This study aims to provide information for drivers or passengers on the air quality in-cabin as there are insufficient data on air quality in-cabin private cars in Malaysia. The objectives of this work are (1) to investigate the concentration of the accumulated CO2 levels in the vehicle cabin continuously while the heating, ventilation, and air conditioning (HVAC) system is set to different ventilation modes with the different number of occupants, car speeds and car cabin size, (2) to identify air quality in terms of the volatile organic compound (VOC) and particulate matter (PM) in the cabin with different conditions, and (3) to analyse the CO2 concentration decay of a parked vehicle with the engine and the HVAC system switched off. The strategies proposed to experiment are by using two modes of ventilation, recirculation (RC) mode and outside air (OSA) mode as shown in Fig. 1. Fig. 1. Types of ventilation in vehicle This research work-study is focused on examining the air quality observed under the HVAC system with the RC mode compared to other ventilation options such as OSA mode. A few scopes of the study were introduced, (1) the study is limited to sites in Malaysia at close to sea level, (2) two different sizes of vehicles are used; small and mid-size cars (3) the number of vehicle occupants is set for 1 person, 2 persons and 4 persons. No history of smoking, no cardiopulmonary disorders such as coronary heart disease, hypertension, diabetes, obesity and other serious diseases were the selection criterion for the car occupants. The occupants are limited to Malaysian who are typically Asian, and (4) the research is conducted by experimental procedure only and not a simulation. The results of the experiment show that the magnitudes of peak CO2 cabin concentrations are greater at the stationary car than at car speeds of 50 km/h. The higher the number the occupants in a vehicle, the shorter the time taken to reach an acceptable 1200 ppm level of CO2. The data also shows that the bigger the cabin area, the slower the accumulation of CO2. Besides that, the PM in the congested road is higher than in the non-congested road. Then, the increase of temperature in-car cabin can affect the concentrations of VOCs. Lastly, when cars are parked for an extended period, the CO2 concentration steadily decreases and eventually returns to an acceptable level.