## 3 CO2 Emissions in Motor Vehicles in the Context of Selected Factors  
CO2 emissions in motor vehicles are a complex process directly related to fuel combustion. From burning one liter of gasoline, approximately 2.3 kg of CO2 is produced, while burning diesel generates about 2.7 kg of CO2 [11]. A review of the literature indicates that CO2 emissions are influenced by several factors, including:  
* vehicle characteristics, such as vehicle parameters (mass, velocity, etc.) [12], type and specifications of the internal combustion engine [13], vehicle type [14], and vehicle profile (aerodynamics) [15],
* type of fuel, such as gasoline, diesel, and alternative fuels [16; 17; 18],
* environmental conditions, such as terrain, ambient temperature, and weather conditions [11],
* driver's driving style [19]. This article focuses on dynamic (instantaneous) parameters related to the vehicle and its engine, including vehicle velocity, engine load, engine speed (rpm), engine power, torque, and throttle position. Vehicle velocity is one of the key kinematic parameters in the context of CO2 emissions, and along with engine speed, it can be monitored and controlled by any driver while operating a vehicle [20]. The optimal vehicle velocity, at which CO2 emissions are minimized, depends on various factors, including the specific vehicle model. One article [21] demonstrates that driving at a velocity of 90 km/h, compared to 110 km/h, can reduce CO2 emissions by approximately 23% (as well as fuel consumption). For most combustion engine vehicles, CO2 emissions increase sharply at velocities exceeding around 100 km/h, particularly above 120 km/h [22]. This is partly due to the fact that air resistance increases with the square of the vehicle's velocity. When it comes to engine speeds, revolutions exceeding around 3000 RPM typically lead to higher fuel consumption and CO2 emissions [22]. This happens because an internal combustion engine, when running at higher RPMs, burns more fuel, directly resulting in greater CO2 emissions [23]. However, CO2 emissions at maximum engine speeds can vary depending on the engine's type and size [24]. Additional factors influencing CO2 emissions include engine power and torque. Engine power determines the engine's capacity to perform work and is the product of engine speed and torque. The trend of increasing engine power in passenger vehicles is one of the reasons why CO2 emissions from road transport in the EU remain high [25]. On the other hand, high torque at low engine speeds allows for dynamic acceleration without the need for the engine to operate at high RPMs, which can lead to reduced fuel consumption and CO2 emissions. Another important factor is engine load, which reflects the intensity of the engine's work relative to its maximum output and influences fuel combustion efficiency [26]. Drivers who tend to accelerate aggressively cause rapid changes in throttle position, which controls the amount of air delivered to the engine. This, in turn, directly affects the air-fuel mixture, leading to increased CO2 emissions [19]. The aforementioned parameters are interdependent. The impact of vehicle velocity on CO2 emissions can vary depending on the engine load and its speed (rpm). Additionally, it is essential to account for differences between various vehicle types and the technologies applied in their engines. The dynamic parameters discussed above reach different values depending on the specific driving cycle of the vehicle [19]. From the perspective of fuel consumption and CO2 emissions, vehicle usage can be divided into three distinct stages: engine startup, urban driving, and highway driving [27]. Each of these stages is characterized by different fuel consumption levels and emissions. The engine startup phase is a short-term stage during which fuel consumption is particularly high. Before the internal combustion engine reaches its optimal operating temperature, it can emit higher levels of CO2 [27].