The Analysis of Exhaust Composition Serves as the Foundation of Sustainable Road Transport Development in the Context of Meeting Emission Standards

Abstract

The main objective of the research presented in this article was to analyze the composition of exhaust gases from passenger cars undergoing periodic inspections and to determine the influence of vehicle age, mileage and the applicable EURO emission standard on the level of emissions of individual components of exhaust gases and thus on the environment. The research was carried out at the District Vehicle Inspection Station in Nowy Sącz, using methods for analyzing the composition of exhaust gases and smoke opacity. The results obtained make it possible to assess whether exhaust emission diagnostics can form the basis for the implementation of a sustainable road transport policy. The study showed that older vehicles emit higher concentrations of carbon monoxide (CO) and hydrocarbons (HC), and diesel cars manufactured before 2010 are characterized by increased smoke opacity. A reliable analysis of the emissions performance of vehicles on the road enables more effective measures to be taken to reduce emissions and improve air quality through regulation, the introduction of clean traffic zones and raising environmental awareness among drivers. This is especially important in regions with specific geographical conditions, such as the Nowy Sącz district, where the terrain—Nowy Sącz is located in a basin surrounded by mountain ranges—favors the accumulation of pollutants and hinders the natural air circulation, leading to the long-term persistence of smog.

1. Introduction

The systematic introduction of air emission limits resulting from the combustion of fossil fuels in transportation, particularly in cities and urbanized areas, is one of the key issues in the energy transition and decarbonization of this sector. When developing systemic solution strategies, it is advisable to focus on the use of so-called emission-free and environmentally friendly fuels, such as biogas, biomethane, biohydrogen, and electricity generated from renewable sources [1,2]. The broadly understood decarbonization of personal, heavy, and public transport should, in the future, ensure the reduction of harmful emissions into the air to mitigate climate change, especially in highly urbanized areas [3].

Currently, transport accounts for 20% [4] of global carbon dioxide emissions and is the most emissions-intensive sector in many developed countries. By adopting the Green Deal, the European Commission aims to take the lead in the pursuit of climate neutrality. The commission’s plans are ambitious, but individual EU countries are at different levels of preparedness for this process. The EU’s goal is to achieve a 90% reduction in greenhouse gas emissions related to transport by 2050 which, according to many experts and researchers, may be unattainable within this timeframe also for social reasons [4].

Diagnostic stations should constitute an integral component of the management system for achieving sustainable road transport objectives, as they facilitate the effective monitoring of emissions from internal combustion vehicles. Regular technical inspections not only ensure compliance with exhaust emission standards but also enable the identification of mechanical faults and the detection of illegal modifications that contribute to increased air pollution. The diagnostic data collected from these stations can serve as a valuable resource for strategic planning and decision-making processes in transport policy, aimed at enhancing environmental efficiency. Continuous supervision of vehicle emissions is crucial for the effective implementation of climate goals and the protection of public health.

2. The Vehicle Diagnostic System and the Achievement of Climate Goals in Road Transport

To reduce the emission of harmful substances into the atmosphere, it is necessary to consider installations that produce fuels from renewable sources and gas transmission infrastructure [5,6,7]. Confronting the European Commission’s plans is a harsh reality: namely, the low share of energy from renewable sources (gaseous biofuels and liquid biofuels) in final energy consumption in transport in Poland, which reached only 5.8% in 2022. It can therefore be concluded that the transition to alternative fuels will be both lengthy and costly for the transport sector [8,9]. For the next 25 years, in various configurations, dependence on fossil fuels in transportation will most likely persist.

To initiate the transformation of transportation and meet the future requirements of sustainable development, it is currently essential to establish and maintain well-equipped diagnostic stations for examining vehicles powered by fossil fuels such as gasoline, diesel, and compressed natural gas [4]. These stations should be responsible for the strict control of exhaust emissions relative to the production year of the vehicles. Diagnostics conducted both at specialized vehicle inspection stations and randomly conducted on roads by mobile measurement units should form the foundation of a monitoring system for the implementation of sustainable road transport objectives and serve as a basis for regulatory decision-making.

The emission diagnostics of combustion engine cars not only allow for the assessment of whether a given vehicle complies with the exhaust emission standard and can therefore be permitted on the road, but also provide broader benefits. These include the following:

• Assessment of the vehicle’s technical condition, which makes it possible to detect various faults and failures that can be repaired before the vehicle is put into operation;.
• Optimization of fuel combustion through service or repair actions;
• Detecting fraud and illegal activities in car mechanics, such as removing the diesel particulate filter (DPF), modifying or removing the catalytic converter, or disabling the AdBlue/SCR system, among others;
• Raising environmental awareness among road users and promoting sustainable development in transportation;
• Conducting a real-world, rather than manufacturer-declared, assessment of emissions from individual power units, along with monitoring their degradation over time.

The indispensable role of diagnostic systems for internal combustion vehicles as the foundation of a low-emission economy stems directly from the very concept of sustainable development. This concept of societal progress aims to balance environmental protection, economic growth, and quality of life while ensuring that future generations can meet their own needs [10]. It is increasingly integrated into the management science literature [11], leading to the assertion that implementing sustainable development requires the integration of management instruments.

Here, a management instrument is understood as a set of means, methods, techniques, and tools used to perform management functions and achieve specific goals [12]. Management instruments are an integral part of the management system and can include strategies, procedures, processes, and specific tools that facilitate decision-making and organizational control [12].

This implies that diagnostic stations can be considered an integral part of the management system for the process of achieving sustainable road transport objectives. This clearly requires the implementation of management functions in achieving sustainable development goals. The classic management functions include planning, organizing, coordinating (resources and activities), leading (commanding, issuing orders, ensuring the execution of the plan), and controlling [13]. Proper diagnostics of motor vehicles, from a managerial perspective, are particularly important in the planning and controlling stages of achieving sustainable development goals. The planning function involves setting specific goals and creating an action strategy to achieve them [13]. It should be based on an assessment of the current state, its conditions through measurement, and comparison with the expected state, taking into account real options for action [14]. It is precisely vehicle diagnostics and the aggregated data derived from them that should become the starting point for planning actions in the field of sustainable road transport development. These data can help analyze and find areas that need improvement. They can also assist in making decisions to improve transport efficiency and environmental impact, showing what changes are needed and how fast they should happen. The second equally important function of management in the area of sustainable road transport, whose implementation requires properly developed and applied automotive diagnostics, is control. The implementation of this function involves monitoring progress in achieving goals, among other things [15]. Without continuous monitoring of metadata obtained from diagnostic stations, the process of effectively managing sustainable road transport and achieving climate goals is not possible.

The main subjects of research and analysis by experts and diagnosticians are internal combustion engines, used to power mechanical vehicles in both quantitative and qualitative terms [16]. In an internal combustion engine, the compression and expansion of a thermodynamic medium, commonly referred to as a gas, are utilized. This gas is used to generate torque or force [17]. During gas compression, less mechanical energy is consumed than during gas expansion [18]. The energy obtained during the expansion of the gas is used to compress it and drive the machine [19]. The combustion of fuel in the engine produces high-temperature gas, which gives the internal combustion engine its name [20].

The gas supplied to the combustion chamber is compressed; it is assumed that the thermodynamic transformation during the compression stroke is an adiabatic transformation [21]. The reduction in volume generates an increase in temperature, which reaches a value between 700 °C and 1000 °C. At this temperature, fuel is also burned. The gas, which has reached the appropriate temperature, expands in the cylinder, which is equipped with a movable piston or turbine [22]. The mechanical energy obtained as a result of the expansion of the hot gas meets the demand for mechanical energy to compress the gas and drive the machine [23].

An important component of a motor vehicle is the exhaust system, which consists of a series of elements designed to remove exhaust gases from the engine, reduce noise emissions, and limit harmful substances [24,25,26]. It is essential for the exhaust system to be airtight and muffle the noise emitted by the exhaust gases while not limiting the power generated by the engine [27,28,29]. The final and most important task of the exhaust system, for both environmental protection and human health, is to clean the exhaust gases of harmful substances, using systems such as the diesel particulate filter (DPF), exhaust gas recirculation (EGR), or selective catalytic reduction (SCR) [30]. The implementation of increasingly stringent EURO 6 emission standards has led to the introduction of new technologies in the automotive industry, responsible for purifying the exhaust gases produced by vehicles [31]. Vehicle manufacturers have incorporated specialized components into the design of the exhaust system [32]. The purpose of these newly developed technologies is to adjust the emission of harmful substances to meet the new exhaust emission standards, which are byproducts of the combustion of the fuel–air mixture in diesel engines [33,34].

Exhaust gases are a multi-component mixture of chemical compounds and pollutants that occur in the form of gases, vapors, and solid particles [35]. Exhaust gases consist of aliphatic hydrocarbons, nitrogen-containing hydrocarbon derivatives, and polycyclic aromatic hydrocarbons [36].

The main compounds present in exhaust gases are nitrogen, a byproduct of combustion, and carbon dioxide, a product of complete carbon combustion [37]. The amount of organic and inorganic carbon in exhaust gases depends on the type of diesel fuel, the duration of the combustion cycle, and the type and technical condition of the engine [38]. A larger mass of solid particles in exhaust gases consists of carbon compared to the soluble fraction. Exhaust gases are mutagenic and carcinogenic agents [39]. Additionally, they cause both acute and chronic changes in the respiratory and cardiovascular systems. Studies conducted by scientists confirm the link between the development of lung cancer and exposure to exhaust gases, which are present in the form of nanoparticles [40]. Nanoparticles can penetrate cell membranes and settle in various parts of the human body [41]. Exhaust gases cause oxidative stress in endothelial cells, making the smallest particles the most toxic to the human body [42].

The characteristics of exhaust gases affect the organoleptic properties of exhaust gases. The dark color of exhaust gases is most often observed in diesel engines and usually indicates a malfunction of the injectors (low pressure in the injection system or a leak in the injection system), the intercooler—the turbocharger cooler (reduced engine power and loud engine operation), or the turbocharger—the turbine rotor [43,44].

Vehicles powered by unleaded gasoline can also emit black smoke during fuel combustion, which is most often associated with an incorrect fuel injection angle or a lack of fuel system maintenance (e.g., failure to replace diesel oil filters) [45]. Another color of exhaust fumes that can be observed is gray, indicating the following faults: malfunctions in the elements that regulate the composition of the fuel and air combustion mixture, engine temperature sensor, or turbochargers, resulting in the presence of oil in the air intake system [46].

The most toxic exhaust gases that can be observed are blue-gray in color, indicating high engine oil consumption, damage to piston rings, and damage or wear to cylinder walls [47,48]. The presence of harmful components in exhaust gases is caused by the combustion of fuel and oil, thermal dissociation, and combustion-related processes, as well as the emission of products resulting from fuel and oil impurities [49].

The products of complete combustion include nitrogen oxides (NO_x), which are the most toxic gaseous components of exhaust gases. They form during combustion at high temperatures [50]. Another unfavorable gaseous component of exhaust fumes is carbon dioxide, which is odorless and colorless [51]. Hydrocarbons (HCs), produced by incomplete fuel combustion, often react with oxygen and nitrogen compounds, forming peroxides and aldehydes [52,53]. Aldehydes are chemically active organic compounds that originate from unburned hydrocarbons that oxidize in the air [54].

Exhaust gases also contain sulfur oxides (SO_x), which react with carbon oxides and particulates. Lastly, solid particles (PM) consist of carbon molecules, sulfur compounds, nitrogen, metals, and heavy hydrocarbons [55,56]. The main types of solid particles include the following:

• PM₁₀—a mixture of suspended solid particles in the air with a diameter of less than 10 μm;
• PM_2.5—fine dust containing particles with a diameter of less than 2.5 μm,
• Micro-particles—particles smaller than 0.1 microns [57,58].

Each of the solid particle types described above is toxic and harmful to the human body [59]. Studies indicate that even a small concentration of PM₁₀ particles has a significant impact on human health [60]. Short-term exposure to PM₁₀ can increase the risk of heart attack and stroke [42]. High-risk groups, for whom inhaling particulate matter can be particularly dangerous, include infants, children, and individuals with lung diseases, allergies, and cardiovascular conditions [61].

Particulate matter is most commonly associated with coughing, shortness of breath, upper respiratory infections, and the worsening of allergies and asthma. PM₁₀ and PM_2.5 particles are also linked to lung cancer [62,63].

3. Materials and Methods

The specific topography of the Nowy Sącz district in Poland causes a tendency to smog in the Sądecka Valley, which is the central geographical area of the region. This situation is caused by the difference in altitude between the city of Nowy Sącz in Poland and the adjacent areas and mountain ranges surrounding the region. As a result, air circulation is hindered and the level of air pollution increases during the periods when the foehn winds are not observed. One of the sources of smog is the exhaust of motor vehicles.

The main objective of the research was to conduct an analysis of the exhaust emissions from passenger cars to determine which cars pose a greater threat to local areas. The research also aimed to establish a correlation between the data collected and the regional air quality. These investigations were conducted using exhaust composition measurements obtained from the District Vehicle Inspection Station in the Nowy Sącz district. The studies on exhaust composition and smoke density required the following actions:

• A written request to the Vehicle Inspection Station to provide the measurements taken on randomly selected vehicles;
• Collection of measurement values recorded on paper;
• Preparation of the analysis of the obtained measurements in a descriptive form;
• Preparation of a graphical analysis of the obtained measurements.

The subject of the research in this study was passenger vehicles that were manufactured between 1983 and 2023. Exhaust composition tests were conducted on 398 vehicles at the Vehicle Inspection Station, which constituted 90% of the vehicles subject to inspection from 1 July 2024 to 30 December 2024 (the remaining vehicles consisted of trucks and electric cars, which were not included in the analysis). Of the 398 vehicles, 222 were equipped with gasoline engines, while 175 were equipped with diesel engines. The research was divided into two phases: the study of exhaust composition of vehicles with gasoline-powered engines and the analysis of exhaust smoke from vehicles with diesel engines.

The first test was conducted using the multi-component exhaust gas analyzer CAPELEC CAP 320 of the model DGA 1500-4 GAS and serial number 11660 (CAPELEC, Montpellier, France), manufactured in 2018. The automotive exhaust gas analyzer was calibrated every 6 months based on the regulation of the Minister of Economy dated 7 December 2007, which specifies the requirements regarding meteorological characteristics [64]. Additionally, the Minister’s regulation of 2 June 2016 stipulates that the measuring instrument must have a high level of metrological protection, which ensures confidence in the measurement results [65]. During the research period, the device had two calibration certificates: the first valid until 29 August 2024, and the second until 3 March 2025.

Each vehicle underwent the test at both the minimum idle rpm and 2500 rpm. Additionally, we performed the second test using a SUN model DGA 1500 absorption opacimeter (Snap-on, Kenosha, WI, USA), which complies with ISO 11614 [66].

An absorption smoke meter is part of a multifunctional test bench for analyzing exhaust gas composition. The degree of smoke opacity is expressed in units of light absorption coefficient, or K [m⁻¹]. Before starting the smoke transparency measurement, the device is automatically calibrated and zeroed. The smoke meter module can be controlled using the exhaust gas analyzer’s keyboard, or the instrument can be connected to an external computer. The table is standardly equipped with probes for measuring oil temperature and engine speed.

The research method and technique involved analyzing the obtained measurements in both graphical and descriptive forms. In order to facilitate the description of the exhaust emissions and smoke opacity measurements, we used the following research instruments:

• Microsoft Excel 2023 for archiving data collected at the diagnostic station, conducting ongoing analyses, and preparing simple data presentations;
• Statistica v12 software for advanced statistical analyses, using analytical tools from the Six Sigma methodology, determining correlations between variables, and creating graphs with extended statistical analysis (e.g., 2D scatter plots);
• A SUN company absorption smoke meter for measuring car exhaust smoke;
• A CAPELEC CAP 320 exhaust gas analyzer for measuring exhaust gas composition and air excess ratio.

4. Results

4.1. Results of the Studies for Gasoline-Powered Vehicles

The characteristics of fuels available in Poland are published by fuel companies such as Orlen. Engines adapted to use unleaded fuel should use unleaded gasoline (95 and 98). They comply with the requirements of the regulation of the Minister of Climate and Environment of 26 June 2002 on quality standards for liquid fuels [67], Annex 1 for E10 petrol, which contains a maximum of 10% (v/v) ethanol.

Table 1. Parameters of gasoline available in Poland.

Parameter	Unit	Range
		Minimum	Maximum
Research octane number (RON)	–	95	–
Motor octane number (MON)	–	85	–
Lead content	mg/L	–	5
Density at 15 °C	kg/m3	720	775
Content of hydrocarbons type:	% (v/v)
- olefinic		–	18
- aromatic		–	35
Benzene content	% (v/v)	–	1
Oxygen content	% (m/m)	–	3.7
Content of oxygen compounds:	% (v/v)
- methanol		–	3
- ethyl alcohol		–	10
- isopropyl alcohol		–	12
- isobutyl alcohol		–	15
- tert-butyl alcohol		–	15
- ethers (with 5 or more carbon atoms)		–	22
- other organic compounds containing oxygen		–	15

Source: Own elaboration based on [68].

shows the declared composition of the petrol.

Diesel fuels such as Ekodiesel ULTRA (ORLEN, Warsaw, Poland) meet the requirements of the regulation of the Minister of Climate and Environment of 26 June 2024 on the quality requirements for liquid fuels, as well as the regulation of the Minister of Climate and Environment of 26 June 2024 on the methods for testing liquid fuel quality. Additionally, they comply with the provisions of the Polish Standard PN-EN 590 Fuels for Internal Combustion Engines—Diesel Fuels—Requirements and Test Methods [67,69,70]. A summary of selected declared fuel parameters is presented in

Table 2. Parameters of diesel fuel available in Poland.

Parameter	Unit	Range
Cetane number	-	min. 51.0
Cetane index	-	min. 46.0
Residue from coking	% (m/m)	max. 0.30
in 10% distillation residue
Remains after cremation	% (m/m)	max. 0.010
Water content	mg/kg	max. 200
	% (m/m)	max. 0.020
Content of solid pollutants	mg/kg	max. 24
Fractional composition for species B, D, F
at a temperature of 250 °C, it distills	% (v/v)	<65.0
at a temperature of 350 °C, it distills	% (v/v)	min. 85.0
Content of methyl esters	% (v/v)	max. 7.0
Residue after distillation	% (v/v)	max. 2

Source: Own study based on data obtained from site [71].

.

The individual exhaust particles emitted by gasoline-powered vehicles that were randomly selected were measured. The CAPELEC CAP 3201 multi-component exhaust gas analyzer (CAPELEC, Montpellier, France) was employed to evaluate 222 vehicles. The test was performed at minimal engine speed (idle), within a range that depended on the vehicle’s make and model, typically fluctuating between 700 and 1000 rpm, as well as at 2500 rpm. The test was conducted in a stationary environment, with the engine running and the transmission in the neutral position, while the vehicle remained immobile.

Manufacturers produced the tested vehicles between 1993 and 2023. We examined the concentration of the following toxic chemical compounds using the exhaust gas analyzer:

• Carbon monoxide (CO);
• Carbon dioxide (CO₂);
• Hydrocarbons (HC).

Furthermore, the coefficient for each measurement was computed using the exhaust gas analyzer. The λ coefficient is a fundamental parameter that characterizes the composition of the fuel–air mixture. This coefficient can be calculated based on the following Formula (1).

$$\mathsf{\lambda }=\left({\mathrm{m}}_{\mathrm{A}\mathrm{I}\mathrm{R}}·{\left({\mathrm{m}}_{\mathrm{F}\mathrm{U}\mathrm{E}\mathrm{L}}·{\mathrm{L}}_{\mathrm{T}}\right)}^{-1}\right)$$

(1)

where

• λ—mixture composition factor—dimensionless;
• ${\mathrm{m}}_{\mathrm{A}\mathrm{I}\mathrm{R}}$—mass of air in the fuel–air mixture [kg];
• ${\mathrm{m}}_{\mathrm{F}\mathrm{U}\mathrm{E}\mathrm{L}}$—mass of fuel in the fuel–air mixture [kg];
• ${\mathrm{L}}_{\mathrm{T}}$—theoretical mass of air needed to burn 1 kg of fuel—is 14.7 [kg] of air [72].

Figure 1 presents the measured fuel–air mixture composition coefficient for both the minimum vehicle revolutions and 2500. The results that were obtained were compared to the permissible limits of the lambda coefficient, which span from 0.97 to 1.03. The value of this coefficient was specified in the regulation of the Minister of Transport and Maritime Economy concerning the scope and method of conducting technical vehicle inspections, as well as the templates of related documents [73].

Moreover, the lambda coefficient allows for the distinction and classification of three instances of the engine’s fuel combustion process as follows:

• λ = 1—means that in the fuel–air mixture there is exactly as much oxygen as needed to burn the fuel, it is referred to as a stoichiometric composition;
• λ > 1—means that in the fuel–air mixture there is more oxygen than is needed to burn the fuel, so some of the oxygen will not be used in the combustion process; it is referred to as a lean mixture (implied in fuel);
• λ < 1—means that the fuel–air mixture contains less oxygen than is needed to burn the fuel; it is referred to as a rich mixture (implied to be rich in fuel).

The results presented in Figure 1A,B indicate a correlation between the year of vehicle production and the fuel–air mixture composition coefficient. Statistica software calculated a Pearson linear correlation coefficient of −0.52 for the idling engine, confirming this. This coefficient indicates a strong correlation between the year of manufacture and the result obtained. For measurements taken at an increased engine speed, the coefficient was −0.14. In both measurement series, this suggests poorer control over the fuel–air mixture in vehicles equipped with older engine designs. One of the reasons for poor fuel mixture control may be the less advanced fuel supply system of older power units or the wear of components due to many years of operation. Vehicles manufactured after 2014 have a λ coefficient at the optimal level of 1. To help determine the best range for this coefficient, the lower and upper limits set by the regulation of the Minister of Transport and Maritime Economy from 7 September 1999 regarding vehicle inspections are shown with black lines. For six vehicles produced between 2014 and 2023, the fuel–air mixture contains as much oxygen as needed for fuel combustion. However, the remaining vehicles produced after 2014 have a fuel–air mixture that contains more oxygen than is needed to burn the fuel. The results indicate that older vehicles exhibit incomplete fuel combustion.

The exhaust emission standards’ permissible values were compared to the measurements of individual chemical compounds that were obtained. Despite not being the primary source of air pollution, we should significantly reduce car exhaust emissions [74]. EU regulations were introduced to limit the impact of exhaust emissions on the environment and human health [75]. The exhaust emission standard for new vehicles presents the maximum permissible threshold for the emission of individual exhaust components, which depends on the year of vehicle registration [76].

Table 3. Emission values for gasoline-powered passenger cars.

Norma	$\mathbf{CO} [\mathbf{g}·{\mathbf{km}}^{-1}]$	$\mathbf{HC} [\mathbf{g}·{\mathbf{km}}^{-1}]$
Euro 1 [77]	3.14	-
Euro 2 [78]	2.2	-
Euro 3 [79]	2.3	0.2
Euro 4 [80]	1.0	0.1
Euro 5 [81]	1.0	0.1
Euro 6 [82]	0.50	0.1

Source: Own study based on European regulations [83].

presents the emission values for gasoline-powered passenger cars. Comparing the results of exhaust gas composition measurements under static conditions at a diagnostic station—expressed as percentage or in [ppm] units—with the EURO standard guidelines expressed in [$\mathrm{g}·{\mathrm{km}}^{-1}$] units is difficult. It requires reference to the actual amount of emissions of the factor in relation to the distance traveled.

Figure 2 presents the CO₂ content graph obtained from the tests conducted using an exhaust gas analyzer at 2500 [rpm].

An analysis of the studies reveals that the highest recorded carbon dioxide values during the research were 16.2% and 16.0%. Conversely, the lowest recorded values were 8.0% and 9.7%. According to the Euro 4 and Euro 5 standards, the permissible upper limit for carbon dioxide emissions is 120.0 $[\mathrm{g}·{\mathrm{km}}^{-1}]$. In contrast, the Euro-6 standard sets the permissible upper limit for carbon dioxide emissions at 95 $[\mathrm{g}·{\mathrm{km}}^{-1}]$.

Figure 3 presents the graph of HC values obtained during tests conducted with the exhaust gas analyzer at 2500 [rpm].

It is not possible to directly compare the results of exhaust gas analysis with the EURO standard guidelines. Studies rely on devices that record exhaust parameters during vehicle operation. In such cases, the key factor is calculating the mass flow rate of exhaust gases and the proportion of individual components. Based on the data obtained under road test conditions, it is possible to accurately determine the amounts of individual exhaust gas fractions emitted per kilometer traveled.

However, it is possible to demonstrate how the new regulations have influenced fuel combustion in internal combustion engines produced during different stages of EURO standard implementation. As a result, this contributes to maintaining optimal fuel combustion conditions and reducing harmful exhaust emissions.

Regarding the aforementioned studies, it can be observed that the highest carbon monoxide content obtained during the tests was 3.62 $[\%]$ for the minimum vehicle revolutions and 4.04 $[\%]$ for 2500 [rpm]. However, the lowest carbon monoxide value obtained was 0.00 [%] for the minimum vehicle revolutions and for 2500 [rpm]. Regarding the Euro 1, Euro 2, and Euro 3 standards, the permissible carbon monoxide emission values are 3.14 $[\mathrm{g}·{\mathrm{km}}^{-1}]$, 2.2 $[\mathrm{g}·{\mathrm{km}}^{-1}]$, and 2.3 $[\mathrm{g}·{\mathrm{km}}^{-1}]$, respectively. However, according to the Euro 4 and Euro 5 standards, the permissible carbon monoxide emission value is 1.0 $[\mathrm{g}·{\mathrm{km}}^{-1}]$, while the permissible value for Euro 6 standards for carbon monoxide is 0.5 $[\mathrm{g}·{\mathrm{km}}^{-1}]$. The change in permissible levels of carbon monoxide in exhaust gases indicates an emphasis on designing internal combustion engines to utilize the fuel’s calorific value as efficiently as possible. This results in the complete oxidation of the carbon contained in the fuel, thereby reducing the CO content in the exhaust gases. Figure 4 presents a graph of carbon monoxide emission measurements from randomly selected vehicles, along with exhaust emission values relative to specific standards. The years of the introduction of subsequent versions of the EURO standard are marked by reference vertical lines.

Analyzing the measurements presented in Figure 2, Figure 3 and Figure 4, it can be concluded that randomly selected vehicles showed a decrease in CO and HC emissions depending on the vehicle’s age. The correlation coefficients in both cases exceeded 0.5, indicating a reduction in CO concentration in exhaust gases to below 0.5% in vehicles manufactured in compliance with the EURO 6 standard. Almost the entire amount of fuel delivered to the engine is oxidized to CO₂ under this standard. Additionally, a more than twofold reduction in HC emissions was observed after the implementation of the EURO 6 standard compared to EURO 1.

4.2. Results of the Research for Vehicles Equipped with a Diesel Engine

The next study involved examining harmful particulate emissions from vehicles equipped with a diesel engine. The research tool used was a SUN absorption smoke meter, which complies with the ISO 11614 standard. The DGA 1500 Kombi absorption smoke meter is part of a multifunctional station for monitoring exhaust gas composition. The degree of smoke opacity is expressed in units of the light absorption coefficient, or K. Before measuring exhaust smoke, the device undergoes automatic calibration and zeroing. The smoke meter module can be controlled using the exhaust gas analyzer’s keyboard, or the device can be connected to an external computer. Standard equipment on the station includes probes for measuring oil temperature and engine speed.

The study involved 175 vehicles equipped with diesel engines. We took five measurements of harmful particulate emissions, also known as smoke opacity. Determining the smoke opacity coefficient allows for the assessment of the amount of solid particles in the exhaust gases. Additionally, an increase in the amount of solid substances in the exhaust gases may indicate poor combustion of the fuel–air mixture.

The lowest average value obtained in the studies was 0.0 [m⁻¹], while the highest was 8.54 [m⁻¹]. Figure 5 presents the results of the exhaust smoke opacity tests. A strong correlation was observed between the data from the analyzed period and the model year of the tested vehicles. The Pearson correlation coefficient for this dataset, at a 0.95 confidence level, is −0.59. The strong correlation is due to two factors. The first factor relates to technical advancements in multi-phase exhaust gas purification (filtration in the car’s exhaust system). The successive tightening of exhaust emission standards has led to the design of exhaust systems in such a way that they effectively remove harmful fractions from the exhaust gases.

The second factor is the technical condition of engines, which deteriorates with vehicle mileage. In vehicles without DPF filters, engine wear leads to increased exhaust smoke emissions. In contrast, in newer vehicles, intensive filtration significantly mitigates this effect.

The standard smoke opacity coefficient that vehicles should not exceed is 2.5 [m⁻¹] [84]. Figure 6 presents a comparison of the smoke opacity measurements (blue dots) with the standard smoke opacity limit (black line).

Based on the data presented in Figure 6, it can be concluded that vehicles manufactured after 2010 have appropriate exhaust smoke emission indicators. One of the vehicles produced after 2010 exceeded the permissible limit of 2.5 [m⁻¹]. The studies mentioned indicate that using higher injector pressure and modern electronic systems that monitor engine performance and manage combustion helps reduce harmful exhaust emissions in diesel engines. An additional factor that contributes to the reduction of toxic exhaust gases is the use of high-quality fuel.

5. Discussion

The research conducted emphasizes the importance of continuous vehicle monitoring in road traffic. The collected data enabled in-depth diagnosis and monitoring of the technical condition of motor vehicles, which should be a fundamental element of sustainable transport management. Reliable data on the emissions of vehicles in road traffic allow for more effective measures to reduce exhaust emissions and improve air quality in cities. This can be achieved through the establishment of clean transport zones, the implementation of legal regulations and guidelines for drivers and their vehicles, the promotion of carpooling, and increasing drivers’ environmental awareness by informing them about the amount of CO₂ they have emitted into the atmosphere since their last technical inspection.

This is especially true in regions with specific geographic conditions, such as Nowy Sącz County and the city of Nowy Sącz, where the lie of the land—the city’s location in a basin surrounded by mountain ranges—favors the accumulation of pollutants and impedes the natural circulation of air, leading to the long-term persistence of smog. According to the 2023 Polish Smog Alert, based on data from the Chief Inspectorate of Environmental Protection, Nowy Sącz ranked among the most polluted cities in Poland. The city recorded 29 days exceeding the permissible PM₁₀ dust standards, and the average annual concentration of benzo(a)pyrene in 2023 was 4 ng/m³ (nanograms per cubic meter), ranking it 7th in Poland [85]. Comparing these data with the average age of vehicles in Sącz region of 16.1 years, according to 2021 data [33], and with the data collected in our own research, it should be concluded that exhaust emissions generated by older vehicles is a significant factor affecting air quality in the region. The average age of cars in the Sącz region, combined with their increased emissivity due to less advanced exhaust reduction technologies and the natural wear and tear of emission control mechanisms, contributes to the persistence of high pollution levels. This points to the need to implement effective measures to reduce emissions, including promoting the replacement of older vehicles with cleaner ones, intensifying technical inspections for exhaust emissions, and developing a transport policy that takes into account low-emission solutions and alternative modes of transportation.

The studies carried out in the work included the analysis of the composition of the exhaust gases and their smoke density. The obtained measurements were compared with the reference values of the exhaust emission standard, and on this basis the measurements were assigned to the appropriate exhaust emission standard. Polish legislation and European Union directives require vehicles to undergo an annual inspection at a diagnostic station, including the measurement of exhaust gas composition. According to the requirements, the spectrum of recorded exhaust components is limited to CO, CO₂, HC, and indirectly O₂ (when obtaining the value of the λ coefficient). The data were archived from 1 July 2024 to 30 December 2024, representing 90% of the vehicles subject to inspection (the remaining vehicles were trucks and electric cars, which were not included in the analysis).

The level of compounds present in exhaust gases, such as CO and HC, under the EURO 6 standard is close to 0 [ppm]. Vehicles meeting the EURO 6 standard have a λ coefficient close to 1, predominantly falling within the range of 0.89 to 1.03, which is a favorable result. This raises the question of whether even more stringent exhaust emission standards for spark-ignition engines could be introduced. The answer lies in European Union legislation.

In 2024, the Council of the European Union approved the plan to introduce the new Euro 7 emissions standard. According to the European Parliament’s arrangements, the new Euro 7 standard [86] will be in effect from July 2030 for passenger and commercial vehicles. However, a year later, the standard will be introduced for buses and trucks. For passenger and commercial vehicles, the current exhaust emission limits established in the Euro 6 standard will be maintained, which confirms the conclusions presented in this article. However, new emission limits will be set for buses and trucks.

Additionally, nitrous oxide (N₂O) will be classified as a regulated pollutant under Euro 7. Passenger cars will also be subject to limits on particulate emissions from brake pads’ PM₁₀. For electric vehicles, the PM₁₀ standard will be 3 $\left[\mathrm{mg}·{\mathrm{kg}}^{-1}\right]$; for passenger cars with internal combustion engines, hybrids, and hydrogen-powered vehicles, it will be 7 $\left[\mathrm{mg}·{\mathrm{kg}}^{-1}\right]$; and for large vans and commercial vehicles, it will be 11 $\left[\mathrm{mg}·{\mathrm{kg}}^{-1}\right]$. In addition, the Euro 7 standard will introduce regulations for the use of batteries in electric vehicles. For example, in the case of passenger cars with an electric or hybrid engine, the manufacturer must ensure that the battery used in the vehicle has a long service life. In addition, the Euro 7 standard will introduce regulations for the use of batteries in electric vehicles. For example, for passenger cars with an electric or hybrid engine, the manufacturer must ensure that the battery used in the vehicle has a long service life. This means that the battery will retain at least 80% of its capacity over a period of five years.

Euro 7 will also introduce an ecological vehicle passport, a document containing data on a vehicle’s environmental impact at the time of its first registration. This document will include information on pollutant emission limits, CO₂ emissions, fuel and electricity consumption, electric range, and battery durability.

6. Conclusions

An analysis of the exhaust gas composition of passenger vehicles carried out as part of the company’s own research showed that older vehicles emit significantly higher amounts of carbon monoxide (CO) and hydrocarbons (HC) than vehicles meeting the EURO 6 standard. The λ coefficient in vehicles manufactured after 2014 is optimal, indicating better control of the combustion process. In older vehicles, incomplete combustion of fuel is observed, which increases harmful emissions. In the case of diesel cars, the oldest vehicles show the highest levels of smoke, which correlates with the lack of modern filtration systems and the degradation of combustion systems. Analysis of fuel parameters indicates that both EuroSuper 95 gasoline and Ekodiesel ULTRA diesel meet current quality standards, but their combustion efficiency depends on engine technology. The results confirm that the successive introduction of EURO emission standards contributes to a significant reduction in emissions. The motor vehicle diagnostics conducted in the article, together with the analysis of air pollution conditions, should form the basis for the implementation of transport policies aimed at reducing exhaust emissions. The implementation of effective regulations, the promotion of modern technologies in motorization and the development of low-emission forms of transport can contribute to improving air quality and reducing the negative impact of transport on the environment, especially in regions with specific geographical conditions, where the terrain favors the accumulation of exhaust fumes and the formation and maintenance of smog.

This paper presents the impact of vehicle age and exhaust emission standards on air quality in a geographically specific region, Nowy Sącz. The study of exhaust gas emissions in the context of EURO standards and the consideration of exhaust gas parameter evaluation in relation to a specific geographic location represent a new approach in the field. The obtained results make an important contribution to the development of automotive diagnostics and the formulation of transport policies aimed at implementing low-emission solutions.

The analysis of combustion efficiency in older and newer vehicles yields interesting conclusions, especially in the context of the lambda coefficient of the fuel–air mixture and exhaust emissions. Older vehicles exhibit lower combustion efficiency, which can be attributed to several specific technical reasons. On the other hand, newer vehicles are characterized by a significant reduction in carbon monoxide (CO) and hydrocarbon (HC) emissions, mainly due to technological advancements, better fuel quality, and more stringent testing conditions.

The result of the research is a significant contribution to the optimization of the development of automobile transportation and to the implementation of new procedures related to vehicle diagnostics.

This study focused only on passenger cars, excluding trucks, buses, and electric vehicles, which also have a significant impact on the environment. This exclusion was a limitation of the analysis. The data collected covered a six-month period, which may limit the ability to draw general conclusions about annual trends. The emission parameters analyzed included only selected chemical compounds, such as CO, CO₂, and HC, without a broader assessment of other potentially relevant substances, such as NO_x or PM₁₀.

In order to overcome the limitations that are currently in place, the authors of the paper intend to expand the scope of the study to encompass other vehicle categories, such as trucks and electric vehicles. They also plan to extend the observation period in order to capture more comprehensive annual trends. Another component of the subsequent analysis will involve the incorporation of additional emission parameters, including NOx and PM₁₀, as well as an analysis of the environmental implications of the recently introduced Euro 7 standards.