Concentrations of combustion products in indoor air can be substantially higher than those outdoors when heating and cooking appliances are used (WHO, 2000). Recently, a number of studies have evaluated the correlation between indoor and outdoor air pollution (Lee et al., 1999). Generally nitrogen dioxide (NO2) and carbon monoxide (CO) are emitted from indoor combustion sources. These comprise tobacco smoke, woodstoves and fireplaces, gas appliances or gas stoves and kerosene heaters (CEC, 1989 and Phillips, 1997). The predominant sources of indoor pollutants are gas cooking (and heating) appliances, which produce complex mixtures of volatile organic compounds, sulphur dioxide, water vapor, particulates, carbon dioxide, carbon monoxide and oxides of nitrogen (Chauhan, 1999).
When we cook with a gas stove, toxic gases like CO, carbon dioxide (CO2), sulfur oxides (SOx), nitrogen oxides (NOx) and all these compounds remain in the kitchen. In developed countries indoor levels of NO2, for example, are affected by gas heaters and cooking ranges (used in 20-80% of houses in some countries). In five European countries, the average NO2 concentrations (over 2-7 days) were in the range of 40-70μg/m3 in kitchens. Peak values of up to 3800μg/m3 for 1 minute have been measured in the Netherlands in kitchens with unvented gas cooking ranges (Harlos, 1987). The most important indoor source of nitrogen dioxide is the use of unvented gas appliances (Moran et al., 1999).