A Projection of Environmental Impact of a Low Emission Zone Planned in Warsaw, Poland

Abstract

A low emission zone (LEZ) is a mechanism for reducing the negative impact of traffic pollution on an urban environment, where exhaust emissions are strictly regulated to meet certain environmental criteria. Such solutions increasing the sustainability of the urban environment are gaining popularity, especially in Western European agglomerations, where there are currently more than 300 zones, mainly in Italy and Germany. Thus far, there are no LEZs in Eastern and Central European countries, but Warsaw authorities plan to launch an LEZ in 2024. According to the ongoing project, the zone is to be implemented gradually, in five stages between 2024 and 2032, and the emission criteria will be tightened accordingly. The gradually reduced emissions of NO_X and PM were utilized as the input dataset in the regional CALPUFF model predictions to calculate the concentrations of these main traffic-induced pollutants within the zone. The direct effect is a reduction in air pollution in the urban center, which is the area most exposed to pollution risk due to heavy traffic. Computer simulations reveal that implementation of the zone in Warsaw will result in a significant reduction in NO_X concentrations within the LEZ, such that its mean concentration in the zone becomes comparable to the rest of the conurbation. However, it will bring only a slight reduction in PM_2.5 concentrations. This results from the long-standing dominance of coal combustion in the Polish economy. This also applies to the urban municipal sector, being clearly predominant over the road traffic contribution. Balance can be achieved once the de-carbonization process has been completed.

1. Introduction

The vast majority of Europeans live in conurbations [1], where they are exposed to the harmful effects of air pollutants [2,3,4], the concentrations of which often exceed WHO limits [5,6], which were significantly tightened recently. Exposure to many of these pollutants, especially particulate matter and nitrogen oxides, poses a serious health risk, often being the cause of premature mortality [7,8,9,10,11,12]. According to [13], the highest number of premature deaths in Europe as a result of heavy traffic and associated nitrogen dioxide emissions has been recorded in major metropolitan areas of Western Europe, such as Germany, Italy, Spain, France, and Belgium [2,6,14]. Also, many Polish cities, including Warsaw, are among the most polluted ones in Europe [15,16]. However, while in Western European cities the impacts of traffic sources and nitrogen oxide emissions are predominant, in Warsaw the greatest threat is posed by particulate matter (PM), emitted mainly by municipal sector sources. This is mainly due to the country’s heavy reliance on coal but also results from the burning of low-quality fuels in residential heating installations.

Transportation is a major source of greenhouse gases and also contributes considerably to local air pollution. The related social costs are significant, ranging from reduced life expectancy and increased infant mortality to far-reaching economic consequences [17,18]. The European strategy for tackling the problem emphasizes the need to de-carbonize the transport sector and to reduce emissions of other harmful pollutants associated with vehicle traffic in cities [19,20,21]. One important mechanism to limit the negative impact of traffic pollution in urban areas that is already implemented in many Western European cities is the creation of low emission zones (LEZs) [22,23,24], also often referred to as clean transportation zones (CTZs) [25,26,27]. These zones are geographical areas where the traffic of the most polluting vehicles is strictly regulated. This usually means that such vehicles cannot move in the area, or the restriction of driving is combined with a charge for admission and/or a penalty for driving in without permission.

The main objective of the zone introduction is to reduce damage to the environment and related risks to residents’ health [28,29,30] since heavy traffic pollutants (NO₂ and PM) are primarily responsible for environmental destruction in the central districts. The main objective is to improve the health of residents by reducing these concentrations. Prospectively, the implementation of an LEZ will create a more sustainable, resident-friendly environment and also curb the recently observed trend of depopulation of city centers. In the long term, it also leads to an improvement in the quality of the environment throughout the conurbation and a reduction in the related social and economic costs of its degradation; thus, it increases the sustainability of future city development.

Usually, city authorities are left with a lot of freedom in defining the related criteria and in deciding whether the condition of the local environment justifies the introduction of such a zone [25]. However, since road transport directly affects air pollution, in the absence of statutory criteria for its environmental impact, it is usually good practice for local authorities to comply with air protection programs when introducing these zones [18,28,31], which comprehensively makes it possible to improve air quality in a given area.

Low emission zones that regulate vehicle traffic in areas where environmental criteria are not met are gaining popularity, especially in Europe. In 2022, there were over 300 LEZs in Europe [25,26,27,32,33,34] in a total of 14 countries. Most zones were established in Italy (172), Germany (78), Great Britain (17), Netherlands (14), France and Sweden (8 each), Austria (6), Denmark (4), Norway (3), and Spain and Belgium (2 each). Greece, Finland, and Portugal each have one low emission zone in their capitals [27]. In addition, some countries intend to significantly increase the number of zones by 2025, for example, France (up to 42) and Spain (up to 149). Implementations of LEZs vary depending on the size and characteristics of the city, and the primary pollutants considered are usually nitrogen oxides and particulate matter [11,35,36,37]. Thus far, no low emission zones have been established in the countries of Eastern or Central Europe and the Balkans, despite very poor air quality in these countries.

Generally, air quality in Poland is one of the worst in Europe. Poor air quality in Warsaw, unlike in most large Western European agglomerations, primarily depends on the level of PM_2.5 concentrations, which mainly come from housing area sources. A similar situation is also observed in most other Polish conurbations, mainly due to the country’s long-term reliance on coal [21,38]. According to [15,16], in 2018, thirty-six of the fifty most PM-polluted cities in the European Union were located in Poland, and in some of these cities, the levels of fine particulate matter significantly exceeded EU limits. In the same year, about 12% of all premature deaths caused by PM_2.5, NO₂, and ozone (O₃) exposures in the EU-28 occurred in Poland. At the same time, Warsaw is one of the most polluted cities in Poland. In particular, in 2018–2019, the average annual concentrations of PM₁₀ as well as fine particulate matter PM_2.5 recorded in the conurbation area significantly exceeded the limits recommended by the WHO [6,12].

Although municipal sector PM_2.5 emissions are the predominant cause of premature mortality and other adverse health effects, road traffic also significantly contributes to air quality deterioration in most Polish cities. In a recent count, it was found that there are over 20 million cars on Polish roads, and 1.5 million are registered every year, of which about 25% are registered in Warsaw [30]. The impact of urban transport is mainly responsible for NO₂ and hydrocarbon pollution but also contributes considerably to the total PM concentrations [21,38]. In 2019, Warsaw was one of the four cities in Poland where NO₂ concentrations often exceeded the annual EU limit, mainly due to transport sector emissions. Electro-mobility and alternative fuels give local governments a new tool that can have a real impact on improving air quality [39,40,41,42]. Additionally, low emission zones can reduce vehicle traffic emissivity in city centers, making them more friendly to residents.

Thus far, only one zone has been built in Poland, a pilot one in Kraków; however, protests quickly ensued. This happened because the very restrictive regulations defining the zone limited the possibility of driving only to fully electric vehicles or ones powered by hydrogen or natural gas. Such a solution lacks social acceptance and increases reluctance to establish such a zone, mainly because there are simply not enough electric vehicles in Poland, nor those powered by hydrogen. As a consequence, there is a real risk of a dead regulation or establishing non-functional zones only in a very small areas, e.g., in the old towns.

Although there are already hundreds of low emission zones operating in Europe, none of them are as restrictive as the one designed in Kraków. For example, London introduced an ultra-low emission zone (ULEZ) in 2019 after 11 years of operation of a low-emission zone (LEZ) [18,29], where not only zero- but also low-emission cars were admitted. Other European conurbations have been following this path for a long time, such as in Oslo, Hamburg, Amsterdam, Paris, Brussels, Madrid, Helsinki, Copenhagen, and Athens. They have introduced bans on conventional cars and limited transit traffic but have also invested in electro-mobility infrastructure, public transport, and car-sharing [30].

To have a real impact on lowering pollution levels in cities, zero- and low-emission cars have to replace conventional cars at a noticeable proportion in order to create an effect of scale [30]. A great deal of responsibility in this regard rests with local governments, which are the only entities able to demarcate areas and create exemptions for some vehicles. In other words, they can implement a zone that meets real needs, e.g., by also allowing admission to it by low-emission vehicles, like plug-in hybrids and classic hybrids. Low emission zones would then have a better chance of being created and accepted by the local community and effectively fighting smog.

The fairly obvious conclusion from the previous implementations of LEZs in European cities is that zone effectiveness in reducing air pollution directly depends on the road traffic in the overall emission field, which is shown in [26] to be the main factor that determines the effectiveness of the zones. The progressive implementation of the zones, i.e., their gradual closing to various types of cars, is more advantageous. They should, first of all, be established by municipalities that know the local restrictions and basic parameters of cars driven in that area. Secondly, they should be created in larger areas, which is more effective in reducing smog. According to [25,27], banning traffic in a small area provokes increased traffic outside the zone, which does not improve the environmental effects and at the same time worsens the comfort of moving around the city. Thirdly, an already existing zone may ultimately affect the social awareness and future purchasing decisions of drivers who, in the face of real restrictions, will pay more attention to the emissivity of purchased vehicles.

2. RDE Emissivity Test in Warsaw and Some Conclusions

As stated above, motor vehicles are a significant source of pollutant emissions in Warsaw, which contribute to the city’s air quality deterioration, particularly in central districts [43]. Any activity aimed at improving this situation should take into account the current technical characteristics of cars in the city, especially in terms of their emissivity. This task has been completed by The Real Urban Emissions (TRUE) initiative, jointly established by the Federation International de l’Automobile (FIA) and the International Council on Clean Transportation (ICCT). This initiative aims to provide city authorities with data on the real emissions of basic vehicle categories operating in the city, broken down by fuel type, mileage, and Euro norm certification. The characteristics covering the basic pollutants determining the urban environment quality (emission data of NO_X and PM_2.5 are utilized in this study) provide key information that is crucial for strategic decision-making, including the design of the low emission zone.

In the autumn of 2020, as a part of the TRUE initiative, real-world emission investigations were carried out in Warsaw. The purpose was to provide detailed information on real car emissions and to support the efforts of the city authorities in the fight against poor air quality. Real Driving Emissions (RDE) tests are needed to reduce the gap between results from laboratory or rolling road tests and those that were emitted in the real world. Using remote sensing technology, over 220,000 valid measurements have been performed, referring to 147,777 unique vehicles in Warsaw. The related reports [18,43] provide a detailed assessment of the actual emissions from the vehicles in Warsaw, as well as some policy recommendations for improving the environmental performance of the cars in the city. In particular, its goal is to help determine how the Warsaw authorities can reduce traffic-induced air pollution. The study also contains a very timely analysis of the city, which started a discussion of the LEZ launch in Warsaw at that time.

Passenger cars are the most common in the sample, accounting for 68% of the vehicles surveyed, followed by vehicles without a specific class (23%), light commercial vehicles (8%), and buses (1%). Emission standards were assigned only to cars for which vehicle class information was available. Vehicles of other classes, such as motorcycles, heavy trucks, and forestry and agricultural tractors, accounted for less than 0.5% of the entire surveyed group.

Moreover, the emissions of imported used vehicles, which are very common in Poland, were also examined within the test, and a solution is proposed to the problem of relatively high emissions from this category of cars [44]. According to the findings [18], imported used vehicles account for 32% of all measurements obtained for passenger cars. The average age of this category of vehicles is more than two times that of domestic-bought ones, and their average mileage is also about 1.5 times higher than that of domestic cars. For all pollutants studied, the average emissions from these vehicles by fuel type are about two times higher than from domestic-bought cars. These high emissions are largely due to the high share of imported cars that are older or have previously been in an accident; therefore, they emit more pollutants. The results obtained in the Warsaw case study are compared with similar investigations of the TRUE study conducted in parallel in Brussels, which helps in better understanding how policies carried out in the two cities affect emissions from light vehicles, vans, and buses.

Figure 1 shows NO_X emissions by fuel type, with breakdowns by emission category and the yearly distance traveled. The average distance driven by a Warsaw car in 2020 was estimated at 7500 km [18]. It can be seen that NO_X emissions from gasoline vehicles decrease with the tightening of standards, while prior to the introduction of the Euro 6 standard, diesel cars show only a moderate improvement. The average levels of NO_X emissions from diesel passenger cars in Warsaw that meet emission standards from Euro 2 to Euro 6 exceed the limits set by regulations. This confirms the results of TRUE studies in other European cities. More specifically, the average NO_X emissions for these vehicles are 1.6 to 4.3 times higher than the limits set by regulations [18]. This discrepancy is additionally highlighted in Figure 1. And still, diesel cars that are formally subject to the Euro 6 norm emit three times more NO_X than their gasoline-powered counterparts. Only diesel vehicles meeting the Euro 6dT and Euro 6d standards show comparable NO_X emission levels.

Also, the PM emissions data collected in the Warsaw study depicted in Figure 2 confirm the results of studies conducted in other European cities. In particular, pre-Euro 5 diesel vehicles, which are not equipped with diesel particulate filters (DPFs), emitted PM at levels 4 to 11 times higher than gasoline-engine cars. The presence of DPF filters has significantly improved the emission results of PM from diesel vehicles under Euro 5; they emitted 80% less PM compared to the Euro 4 diesel vehicles. Also noteworthy is the relatively high level of PM emissions observed for gasoline vehicles meeting the Euro 1 to Euro 3 standards, as these older gasoline cars were more common than older diesel vehicles among all vehicles surveyed in Warsaw.

Although the average PM emissions from diesel vehicles have decreased dramatically since the introduction of the Euro 4 standard and have been reduced due to the use of DPFs, improper maintenance, aging, intentional tampering, or the removal of DPF filters can again increase levels of PM emissions from individual vehicles. The improper operations and modifications of DPF filters observed in Warsaw vehicles confirm the findings of an earlier TRUE study in Brussels. The study also revealed that PM car emissions often exceed the required limit, which suggests that malfunctioning DPFs or those that have been tampered with may be a more common problem.

It is strongly recommended in [17] to immediately withdraw vehicles certified below the Euro 4 standard, regardless of the fuel type. These cars are more than 15 years old and currently account for 37% of NO_X and 51% of PM emissions. That is a disproportionate share of pollution in relation to their share of traffic. The proposed policy also calls for banning, at an early stage, Euro 4 and Euro 5 diesel vehicles, which are responsible for 27% of NO_X and 28% of PM total emissions. The environmental benefit of this proposal is reducing the use of old vehicles, which are usually operating beyond the required emission lifetime [43] and are characterized by increased emissions.

3. Characteristics of the Low Emission Zone Planned in Warsaw

The creation of the low emission zone by the Warsaw authorities is a response to residents’ demands for improving air quality. The topic has been raised repeatedly by NGOs and social movements concerned with the health and quality of life in the city. The implementation of the LEZ is also an obligation of the Warsaw authorities, resulting from the implementation of an air protection program for the Mazovian Voivodeship [45]. In Poland, a sufficiently softened version of the earlier unsuccessful LEZ project has already been adopted in Kraków, where the zone is to take effect in 2024. The authorities of Wrocław also presented their own project.

The Warsaw authorities intend to implement in 2024 the first stage of the zone, which will restrict the most polluting vehicles from driving in the city center [46]. The area of the zone, the subsequent deadlines for tightening limits, and the requirements or exceptions for selected groups of people or vehicles are the subject of public consultations. Due to the project [47,48], the zone (covering about 8% of the city domain) will be in place starting July 2024 and will cover most of the center and adjacent parts of the neighboring districts. The zone’s boundaries will coincide with the major roads and railroads that will not be included in the zone. The western and southern boundaries of the zone are formed by the major arterial streets, while the railroad bypass bounds the zone to the east and north. The planned zone’s area is shown in Figure 3.

The project of LEZ creation in Warsaw takes into account all the important TRUE [17,18,43] recommendations discussed in the previous sections [17,18,43]. In particular, this means very strict limitations for the pre-Euro 4 diesel engines from the first stage of the zone’s launch. The entire process of implementing the zone has been divided into five two-year stages. In the first stage (starting in 2024), the LEZ driving restriction will apply to pre-Euro 2 gasoline vehicles (older than 27 years) and pre-Euro 4 diesel vehicles (older than 18 years). Then, every two years, the requirements for emission standards (and the related vehicle age) for gasoline and diesel cars traveling in the zone will be increased until the final stage, starting in 2032. Figure 4 shows details on the subsequent steps of the zone implementation [46]. The City Council may also decide to expand the zone in the future. Such a decision, however, will require prior consultation with the residents.

The increasing requirements for vehicles in both the gasoline and diesel categories will result in an appropriate reduction in emissions, both NO_X and PM, in consecutive stages. The results of the RDE emissivity test [18] discussed in Section 2 and especially the emissivity results presented in Figure 1 and Figure 2 were utilized to quantify the expected reduction in NO_X and PM emission levels after implementation of the subsequent stages of the zone. Although the details are not yet fully specified, in the model simulation, it is considered that emission restrictions also pertain to zone residents, while exceptions are planned for service vehicles.

The estimates were obtained taking into account natural vehicle replacement by new ones at the subsequent stages of meeting more restrictive emissivity standards.

Table 1. The expected NO_X and PM emission reductions in the zone resulting from LEZ implementation.

	STAGE	ST 1 (2024) E2 (G) E4 (D)	ST 2 (2026) E3 (G) E5 (D)	ST 3 (2028) E4 (G) E6 (D)	ST 4 (2030) E5 (G) E6dT (D)	ST 5 (2032) E6 (G) E6d (D)
EMISSION
NOX	Gasoline/diesel share	41%—G 59%—D	42%—G 58%—D	51%—G 49%—D	52%—G 48%—D	55%—G 45%—D
	Total emission reduction	11%	23%	49%	66%	75%
PM	Gasoline/diesel share	62%—G 38%—D	56%—G 44%—D	59%—G 41%—D	62%—G 38%—D	60%—G 40%—D
	Total emission reduction	32%	55%	66%	70%	73%

presents the assessed reduction in the total NO_X and PM emissions during implementation of the subsequent stages of the zone. The indicated percentage reductions in emissions of major pollutants are comparable to the estimates presented in [46].

4. Simulation Results

In order to assess the influence of the zone implementation on the atmospheric pollution in the Warsaw conurbation, modeling of pollutant dispersion in the city was carried out using the Lagrangian Puff Model CALPUFF v 7.0 [49]. This model has been applied for modeling air quality in the Warsaw metropolitan area previously. The results of the model performance validation were presented in [50,51], and they are not repeated here. In this study, the model simulation was used to calculate the average annual concentrations of the main pollutants in the city, with a focus on the LEZ area.

The area considered in the computations encompasses Warsaw (about 520 km² within administrative boundaries) and its immediate surroundings, i.e., a strip approximately 30 km wide (Figure 5). The emission field includes three categories of sources, located both in the city and in the surroundings (their numbers are given in parentheses): (a) point sources (4073), (b) traffic line sources (1806 + 4918), and (c) municipal area sources (1452 + 5819). The transboundary pollution inflow, including the primary and secondary pollutants, was also considered [38,51].

The spatial resolution applied in the computer simulation is a 0.5 km × 0.5 km homogeneous grid inside Warsaw as well as in the surrounding satellite cities and 1 km × 1 km in the vicinity belt. The input dataset for the year considered includes the main meteorological fields re-analyzed by the mesoscale numerical WRF model and then transformed by the CALMET preprocessor to the input data required by CALPUFF [50,51]. The ozone concentration for the simulated year, important for NO_X formation [51,52], is entered as an exogenous variable. The simulations were performed for emission and meteorological data in 2018 (representing the baseline emission dataset) and for emissions attributable to the implementation of the subsequent LEZ restrictions, as discussed above. The related annual mean concentration maps for the basic polluting compounds, NO_X and PM_2.5, are presented in Figure 6 and Figure 7.

Figure 6a presents the annual mean NO_X concentration map for the baseline (2018) emission data. Figure 6b,c show the NO_X concentration maps after launching stage 3 (2024) and stage 5 (2032) of the LEZ, respectively. These maps show a significant reduction of about 36% of NO_X concentration within the zone. The launch of the zone also has some minor impacts on the average concentration of a given pollutant throughout the city. In this case, the city-wide averaged NO_X concentration, after the activation of the final stage of the LEZ, drops by about 1–1.5 μg/m³ compared to the baseline data. The map shown in Figure 6d takes into account the reduction in municipal sector emissions as a result of an ongoing anti-smog program, as well as the comprehensive modernization of the transportation sector. As shown in [21], the implementation of these projects will additionally reduce NO_X emissions by about 25%.

In a similar way, Figure 7 shows the impact of LEZ activation on PM_2.5 concentration in the city. In this case, however, the effect of launching the zone is far less spectacular when compared to NO_X. The maps in Figure 7b,c, depicting the activation of stages 3 and 5, show a slight reduction in concentrations within the zone boundaries. Concentrations averaged within the entire zone decrease by about 1.0 μg/m³ as compared to the initial state shown in Figure 7a. A significant reduction in PM_2.5 concentrations throughout the city is achieved in this case by the implementation of the anti-smog project in the municipal sector (Figure 7d).

The fundamental difference in the effectiveness of LEZ for the two pollutants presented reflects the structure of the fuel mix in Poland. In particular, for the baseline data, the NO_X concentration average for the city is 25.8 μg/m³, while within the LEZ boundary it is 35 μg/m³; it is much higher in the LEZ due to the high volume of vehicle traffic inside the zone. After full implementation of the zone, the corresponding concentrations are 24.4 μg/m³ and 23 μg/m³, respectively, i.e., the average concentration in the zone is even lower than in the city. The difference remains when the anti-smog modernization projects are completed, where the final concentrations are 18.4 μg/m³ and 16 μg/m³, respectively. The analogous differences for PM_2.5 concentrations are much smaller, and for Warsaw and the LEZ, they are 19.9 and 19.7 for the baseline data, 19.08 and 18.8 for the LEZ implementation, and 15.9 and 15.0 resulting from the modernization of the emissions of the municipal sector due to the anti-smog program, respectively.

The evident discrepancies In the zone’s efficiency with respect to emission reductions of the above key pollutants are additionally explained in Figure 8. This figure shows the emission source apportionments for NO_X and PM_2.5 pollutants. The former (left panel) depicts that full NO_X emissions consist of above 50% from the line (traffic) source contribution, mainly those in the city (Line_waw, yellow). Thus, launching the subsequent zone stages results in a significant reduction in NO_X concentrations within its borders. Additionally, a quite important contribution of the area sources, and especially external inflow, results in a definite reduction in concentrations within the city when the anti-smog modernization program is completed. The mean NO_X concentration inside the LEZ in each case remains lower by about 2 μg/m³ than the average city value.

The right panel in Figure 8 shows that the area sources of the municipal sector (red) have a predominant share in the final PM_2.5 concentration, while at the same time the contribution of traffic is minor. Mainly, only the primary traffic emissions (yellow), which are moderate, are reduced by implementing the LEZ restrictions. For this reason, the subsequent maps in Figure 7 show only minor changes in PM_2.5 concentrations associated with the activation of the consecutive LEZ stages. On the other hand, due to the dominating impact of the area sources as well as the transboundary inflow, the launch of the overall (for the surrounding region) anti-smog modernization program results in a clear reduction in pollution throughout the city. The PM_2.5 concentration levels inside and outside the zone remain close to each other.

The effectiveness of LEZ implementation can also be expressed in the reduction in population exposure.

Table 2. Comparison of the population exposures to the main pollutants (μg/m³) connected with LEZ implementation.

STAGE		Baseline (μg/m3)	3rd Stage (μg/m3)	5th Stage (μg/m3)
NOX	City	26.0	25.1 (−3%)	24.7 (−5%)
	LEZ	34.6	27.1 (−22%)	23.3 (−33%)
PM2.5	City	20.59	20.55 (−0.2%)	20.52 (−0.3%)
	LEZ	19.73	19.11 (−3%)	18.79 (−5%)

presents population exposures to NO_X and PM_2.5 averaged over the entire city and LEZ domain, respectively.

The last three columns in Table 2 present the average exposure to NO_X pollution presented in the maps in Figure 6a–c and the average exposure to PM_2.5 pollution shown on the maps in Figure 7a–c. LEZ implementation changes the NO_X exposure values in the same way as the average concentrations. In particular, the exposure inside the LEZ in the base year is much higher than the exposure for the city as a whole, but becomes smaller after full implementation of the zone. Also, in the case of particulate matter, the spatial distribution of the exposure coincides with the corresponding map of PM_2.5 concentrations, which is the result of a fairly uniform distribution of population density in Warsaw. In this case, the effect of the zone’s implementation on changes in exposure values is negligible, but exposure to PM_2.5 in the LEZ is always lower than in the city as a whole, including in the baseline year. This is due to the dominant contribution of the municipal sector to PM_2.5 concentration, with only a small contribution by transportation (cf. Figure 8), and the fact that a major part of the dominant PM_2.5 emission sources is located outside the LEZ.

The numerous implementations of LEZs presented in the literature differ not only in the size of the cities, the zone itself, and the approach applied, but also in the main criterion used to assess the effectiveness of a given implementation. This may be the concentration of the main pollutants, the exposure of the residents, or the resulting health effects. Since car traffic is in this case the main source of air pollution, a natural indicator of the zone’s effectiveness is reduction in NO_X concentration, often supplemented by PM pollution. Hence, NO_X concentration is a reliable indicator when comparing different LEZ implementations. In particular, it was shown in [29] that the LEZ in London caused a NO_X concentration reduction of 17%, while the additional ultra-LEZ activation increased the reduction up to 20%. At the same time, the Malmö LEZ activation [23] provided a 13.5% reduction, while in Haifa [33] it was about 13%. The implementation of the LEZ in Greater Paris [35] showed a reduction in residents’ exposure to the combined NO₂ and PM_2.5 pollution by about 20%. Thus, given the substantial differences in approaches used in the analyses and taking additionally into account that the share of old vehicles in Warsaw is much greater than in the abovementioned cities, the results obtained in our study can be considered comparable. Significant differences are seen in the case of PM pollution because, in this case, the contributions from sources other than car traffic are more important [24].

5. Summary and Discussion

This study presents technical assumptions and the expected effects of activating a low emission zone in Warsaw, the first stage of which is to be launched in July 2024. In planning the zone, the experience and principles of good practice established in the activation of numerous zones in Western European cities were taken into account. The general strategy of low emission mobility in European conurbations emphasizes the need to de-carbonize the transportation sector and reduce its related harmful emissions. In most West European Union countries, different policies are implemented to support the development of electro-mobility, micro-mobility, and car-sharing that involve, for example, exemptions from road taxes and registration taxes, financial benefits, and free parking areas in some cities. Moreover, in most of the major cities, LEZs are implemented to limit the negative impact of traffic on air quality in selected urban areas. Currently, as stated above, there are over 300 LEZs in Europe, but surprisingly, there are no such zones in Central and Eastern European (CEE) cities, even if the air quality in this region is often much below the accepted WHO air quality norms. This also applies to Poland, one of the largest CEE countries.

The design of Warsaw’s LEZ takes into account the principles developed earlier for zone creation as well as the recommendations of institutions performing the RDE tests for the transport sector [17,18,25,43]. These rules suggest, among other things, a gentle and gradual introduction of the zone and broad public consultation on the planned restrictions and possible future expansion of the zone’s boundaries, but also a rapid exclusion of traffic of the most harmful diesel vehicles.

However, the results presented in the paper show that despite the inclusion of generally recommended rules, the effectiveness of the zone in reducing the negative impact of transport on the urban environment is different than in Western European cities, where road traffic is the main source of nitrogen oxide and particulate matter concentrations. In Warsaw, the predominance of coal combustion in the national economy, which is also evident in municipal emissions, is mainly responsible for particulate matter emissions (see also [9,21]), with a noticeably smaller contribution from transportation, as is quantitatively explained in Figure 8. A similar problem is likely to persist in other CEE countries, although with different intensities. For this reason, as shown in Section 4, the activation of the subsequent LEZ steps results in a substantial reduction in NO_X concentrations in the zone, accompanied by only a slight decrease in PM_2.5 pollution. The latter is determined by particulate matter emission from the municipal sector but is also due to transboundary inflow. A similar problem is to be expected in other Polish cities, such as Kraków or Wrocław, which are currently launching LEZs. A more balanced contribution of road transport and the municipal sector to particulate matter emissions will only be possible when the ongoing de-carbonization process has been completed [21]. This situation is visualized by the NO_X and PM_2.5 concentration maps shown in Figure 6d and Figure 7d, respectively.

A well-known problem affecting the final emissivity of cars in Warsaw is the high share of imported used cars. The inflow of older, higher-emission vehicles should be prevented. This can be achieved by introducing a nationwide policy limiting the age of imported vehicles. Such a policy could also be complemented by other measures, such as scrappage programs, tax breaks, and other financial incentives discouraging the purchase of old vehicles. At the local level, the problem of emissions from imported used vehicles can be addressed by introducing road traffic restrictions connected with the age of vehicles or emission standards.

The creation of the LEZ in a city will have a direct impact on reducing the level of air pollution within the zone, in addition to, albeit to a lesser extent, in its closer surroundings. However, an indirect goal of the zone’s restrictions is also to modify the shopping habits of drivers, in particular the very popular practice in Poland of purchasing used cars. Very restrictive norms related to age and mileage may discourage the purchase of the most polluting old cars. This effect may be enhanced by the government’s limitations on used car imports. A similar importance is attached to the consistently increased restrictions on vehicle emissivity that come along with the activation of the subsequent phases of the zone. Regarding this, a problem has arisen with the planned Euro 7 emissivity legislation, which aims to introduce emission durability requirements of up to 15 years or 240,000 km for certified vehicles. However, the age and mileage of around 30% of vehicles used in Warsaw are higher than those specified by the requirements [18,43]. This suggests that considering longer lifetimes may be necessary to accurately represent the usage of passenger cars in Polish and other European cities.

The high potential for reducing air pollution emissions from urban transportation is connected with the possible expansion of electro-mobility, while at the same time, there are not many BEV and HPEV cars operating in Warsaw. In the last two years, the number of electric cars in Poland has more than tripled, and also more than 600 new charging stations were installed in Poland in 2022 [41,42]. This is a better result than in previous years, but still not enough to meet the ambitious targets set by the EU regulations [52]. In a realistic scenario [53], which assumes the introduction of subsidies at an increased level in relation to the pilot program launched in 2020, the Polish all-electric vehicle fleet in 2025 may number around 300,000 units, and about 25% of new cars are usually registered in Warsaw. Additionally, the recently adopted regulation of the European Union that considers the discontinuation of the registration of new combustion-engine cars in the EU after 2035 [52] should increase drivers’ interest in purchasing electric/hybrid vehicles, particularly because many car companies are modifying their production profile towards electro-mobility. However, the real environmental effect of urban car modernization in Poland will not be fully seen until the process of de-carbonization of the energy and municipal sectors, supported by the actual development of green energy sources [21], is completed.