###### Abstract
Urban areas typically have higher NO\({}_{2}\) environmental concentrations, primarily attributable to traffic emissions [29]. Overall, the outdoor NO\({}_{2}\) source contributed 73-76% of the NO\({}_{2}\) in the kitchen [30]. These authors found that outdoor NO\({}_{2}\) sources were present indoors all the time; by contrast, indoor NO\({}_{2}\) sources were present sporadically but with a very high contribution. Typically, higher NO\({}_{2}\) concentrations are found in rural kitchens than in urban ones. This happens as NO\({}_{x}\) emissions are related to the power of indoor sources. [PERSON] et al. [31] found that NO\({}_{x}\) emissions are linearly related to the amount of natural gas burned (\(r^{2}=0.76\); \(p<0.01\)). Furthermore, in a recent literature review conducted by [PERSON] and [PERSON] [9], it was concluded that the indoor-to-outdoor (I/O) NO\({}_{2}\) concentration ratio is primarily influenced by human activity patterns and ventilation. Typically, the I/O ratio of residential buildings exceeds 1 due to the substantial NO\({}_{2}\) emissions during cooking and smoking, combined with relatively low ventilation rates. Near 80% of the NO\({}_{2}\) in indoor air is removed during the first hour after it is emitted ([PERSON] et al. (1989) in [2]). However, in some cases, NO\({}_{2}\) can react and form other compounds such as NO and nitrous acid. Cooking burner pollutants that are not exhausted directly by a range hood are removed from the air in the home by air exchange with the outdoors and, for NO\({}_{2}\), by deposits on interior surfaces. In the U.S., the reaction rate for NO\({}_{2}\) is estimated to be of 0.8 h\({}^{-1}\)[32]. Besides emission sources, other factors may influence pollutant concentrations. [PERSON] et al. [15] examined eight conditions involving fuel type (electricity or natural gas), cooking type (boiling water or cooking), and ventilation (with or without), indicating that both the period and style of cooking affect pollutant levels. [PERSON] et al. [23] developed a model that combined the presence of sources of combustion products and the ventilation characteristics in the kitchen to determine the 'Chance of Accumulation of Combustion Products' in the kitchen. Ventilation is one of the main factors affecting indoor concentrations. [PERSON] et al. [31] discovered that families who do not use their range hoods or have poor ventilation can exceed the 1-h standard of NO2 (100 ppb) within minutes of stove usage, especially in smaller kitchens. Some kitchens have \"ductless\" hoods that recirculate fumes through activated charcoal filters, which are generally less effective at cleaning the air. However, since exhaust hoods are separate from the stove and must be operated manually, they are used, in practice, only 25-40% of the time [27; 33]. Vented hoods vary in effectiveness and work best when positioned directly over the stove [26]. [PERSON] et al. [34] observed that NO2 decay rates were much faster with a forced air unit operating, suggesting the effective removal of NO2 by the air handler, and [PERSON] et al. [20] found that mechanical exhaust systems are more efficient than natural ventilation in removing pollutants. The literature review has enabled us to identify that studies on NO2 exposure, considering both indoor and outdoor levels, have been conducted since at least the 1980s for different cities. These studies typically compare different fuel types under various environmental, ventilation, or cooking conditions. However, the focus has often been narrowly limited to measuring indoor and outdoor NO2 concentration levels, neglecting the critical study of human exposure. This oversight limits the development of more comprehensive and robust government policies for human health protection, which currently tend to focus primarily on assessing and controlling outdoor air quality levels. In this study, the main objective is to assess the effect of the use of NG in kitchens on human exposure to NO2 under different outdoor air quality levels.