## 1 Introduction  
Car combustion engines generate emissions of many air pollutants, such as dust (PM\({}_{2.5}\), PM\({}_{10}\)), hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO\({}_{2}\)) and nitrogen oxides (NOx) [1]. Carbon monoxide is particularly dangerous and has an impact on human health and life. Carbon monoxide is a highly toxic, odorless and colorless gas, slightly lighter than air, which means it easily mixes with air and spreads indoors [2,3]. Potential sources of carbon monoxide in living rooms include heat sources and devices for heating domestic hot water in which fuels are burned. Carbon monoxide is produced as a result of an incomplete combustion of many fuels, such as coal, wood, fuel oil, gasoline,kerosene and gas, in the absence of an adequate amount of oxygen. The danger of carbon monoxide poisoning stems from the fact that carbon monoxide is undetectable by humans, it enters the body through the respiratory system and is then absorbed into the bloodstream. In the human respiratory system, carbon monoxide binds to hemoglobin 210 times faster than oxygen, blocking the supply of oxygen to the body, which poses a serious threat to human health and life. Carbon monoxide prevents the proper distribution of oxygen in the blood and causes damage to internal organs and, above all, to the brain. Acute poisoning may result in coronary failure and irreversible damage to the central nervous system [2; 3; 4; 5; 6; 7]. In garages, where cars are parked, the main sources of carbon monoxide emissions are the internal combustion engines of passenger cars. The literature contains research on carbon oxide concentrations in rooms where cars are parked or repaired [8; 9; 10]. In the Quebec City region [8], 33% of car repair shops and car showrooms had atmospheric CO concentrations above 25 ppm, a level considered to pose a risk of affecting chronic health. In a single-car garage, with a volume of 73 m\({}^{3}\)[9], after 20 min of running the car, the carbon monoxide concentration level was 253 ppm for a car without a catalytic converter, and 30 ppm for a car with a catalytic converter. Research on a parked passenger car in the garage of a single-family house showed a carbon monoxide concentration of 420 ppm after 47 min of the car running. It should be noted that the gaseous pollution in rooms is also associated with sick building syndrome (SBS) [11; 12]. In multi-car garages, the concentration of carbon monoxide depends primarily on the number of cars and the type of ventilation installed [13]. Carbon monoxide emitted by cars affects the level of carboxyhemoglobin (HbCO) in the blood of employees operating garages in city centres [14]. According to the research presented in [15], most of the deaths caused by carbon monoxide, unrelated to fires, took place in garages or outbuildings. CFD (Computational Fluid Dynamics) programs are used to determine the three-dimensional problems, in order to accurately simulate the concentration of air pollutants in rooms [16; 17; 18]. One-dimensional models are also used in air quality simulations [19; 20; 21], and can be used in automatic indoor air quality control systems [22; 23; 24]. Smaller single-family houses are currently being built in Poland due to the increasing building, purchasing, and operating costs [25; 26]. Smaller houses are also most often characterized by garages with a small volume. Carbon monoxide is particularly dangerous in rooms with a small number of air changes and in rooms with a small volume. The aim of this study is to present the results of research on CO concentrations in a single-family building garage when the combustion engine of a passenger car is turned on and with various air exchanges in the garage. This study also develops a one-dimensional model for estimating the carbon monoxide concentration in a small garage of a single-family building equipped with exhaust ventilation.