Car cabin air quality sensors and systems (2006)

It is not surprising that air quality in vehicle cabins is usually found to be worse than that typically found in homes or workplaces, especially when so many exhaust pipes are only inches away from adjacent vehicles. Pollutants find their way into the cabin via the ventilation system, also known as the Heating, Ventilation and Air Conditioning (HVAC) system. Independent studies [1–3] have shown that vehicle cabins commonly show concentrations of toxic gases such as carbon monoxide (CO), hydrocarbons (HC), volatile organic compounds (VOC), and oxides of nitrogen (NOx) higher than safety limits set by Occupational Safety and Health Administration (OSHA) and World Health Organization (WHO). As experienced by most, discomfort due to offensive smells is the prime concern regarding pollutants in vehicle cabins. However, more serious are the adverse health effects that result. The most dangerous is fatigue. Driver fatigue is a primary concern in the battle to decrease road fatalities. A media announcement from the Department of Transport in Australia, states that fatigue is the principal cause for 20% of crashes involving a fatality [4]. Fatigue is often associated with feelings of drowsiness or sleepiness, loss of alertness, inability to concentrate, and slowed reactions. Aside from lack of sleep, fatigue symptoms can derive from exhaust pollutants such as CO, NOx, and HC’s causing headaches, nausea, and dizziness and inducing poor hand-eye coordination that may increase the likelihood of a collision [5, 6]. Further, in a confined environment, our natural breathing process too can compound these effects and aggravate the health hazard. In the course of breathing, we exhale CO2, which can displace O2 in an indoor environment such as a vehicle cabin, leaving the environment O2 deficient. Such high CO2 and low O2 concentrations can cause adverse human health effects. This situation is amplified when vehicle occupants choose to operate the HVAC system in the “closed/recycle” mode aiming to prevent outdoor-polluted air from entering. Various independent studies [2–4] have also shown that through this process, the concentrations of O2 and CO2 may come to exceed safety limits set by OSHA. Interestingly, a study on fatal single vehicle crashes highlights that the vehicle is more likely to have closed windows and a heater on, than to have fresh air and air conditioning fitted [7]. An O2 deficient environment has been termed “hazardous” by OSHA when the O2 concentration is less that 19.5% [8]. Low O2 levels can impair judgment, increase heart rate and impair muscular coordination. Another overlooked issue concerning vehicle cabin air quality are motor vehicle exhaust gas suicides caused by CO poisoning [9–12]. Of the 2,320 suicides registered for the year 2002 in Australia, statistics indicate that 416 persons (18%) died from motor vehicle exhaust gas [13]. Many deaths are also attributed to unintentional CO poisoning in and around motor vehicles. A study of U.S. deaths found that 57% of unintentional CO poisoning deaths occurred in automobiles [14]. In recent years, new innovative sensors, systems and aftermarket products have been introduced in an attempt to alleviate vehicle cabin air quality concerns. The sensors and systems that achieve this will be the focus of this chapter.