The Inventory of Pollutants Hazardous to the Health of Living Organisms, Emitted by Road Transport in Poland between 1990 and 2017

The paper provides the results of the inventory of pollutants hazardous to the health of living organisms, emitted by road transport in Poland between 1990 and 2017. For estimating pollutant emissions from road transport, a standardized methodology was applied, consistent with the guidance of EEA/EMEP Emission Inventory Guidebook 2019 and the COPERT 5 software. The following substances were analyzed: carbon monoxide (CO), non-methane volatile organic compounds (NMVOC), nitrogen oxides (NOx) and particulate matter size fractions (total suspended particles—TSP, PM10, PM2.5). For the pollutants, emission values averaged over the distance travelled by the road fleet (average specific distance emission) were determined. The results obtained indicated that between 1990 and 2017 the annual pollutant emissions from road vehicles in Poland had an increasing trend concerning TSP (74%), PM10 (64%), PM2.5 (52%) and NOx (25%), while the corresponding emissions had a decreasing trend for CO (−117%) and NMVOC (−85%). However, a clear downward trend was found for the average specific distance emissions of all substances throughout the subsequent inventory years: TSP (−28%), PM10 (−100%), PM2.5 (−91%), NOx (−84%), CO (−208%) and NMVOC (−173%), which is due to the dynamic progress in the technological advancement of road vehicles.


Introduction
Air pollution from anthropogenic sources contributes to climate change and is recognized as a major environmental health risk to human health. It is clear that pollutant emissions need to be reduced or at least stabilized in a possibly effective way in order to counter these negative effects and to achieve sustainable development. The successful implementation of air quality plans, new policies and commitments depend on detailed estimation of emissions of hazardous substances [1]. Therefore national inventories of pollutant emission arising from human activities have been established in the majority of developed countries and reported to the international organizations. The reported inventories of air pollutants are commonly accessible, as, e.g., the report for the EU [2,3], the United States of America [4] and Canada [5].

Methods
The adopted modeling approach is based on the assumption that the total pollutant emission from road transport is a superposition of pollutant emission released from individual vehicles. This is justified, since the intensity of the emission of particular pollutants is an additive quantity [7,9]. Another assumption is that the substances are in the state in which they were emitted from vehicles, i.e., they do not undergo physical and chemical changes in the environment [7,9].
National emission of pollutants from motor vehicles is the sum of annual emission from all vehicles driven during the calendar year in the country: where: E ax -national emission of pollutant "x", b ix (t)-specific distance emission of pollutant 'x' from vehicle 'i' at time 't', τ-integral variable with time dimension: τ ∈ <t;t + 1>, t-time-year number (in calendar years): t ∈ <1990;2016>, N-total number of vehicles. Specific distance emission of pollutant is a derivative of pollutant emission to the distance traveled by the vehicle [7]: b(s) = dm(s) ds (2) where: b-specific distance emission of pollutant as a function of the distance traveled by the vehicle, m-emission of pollutant 'x' from the vehicle, s-distance traveled by the vehicle. All vehicles are classified into categories. The basic criteria for classifying road vehicles may vary, but the following have most often been adopted [9,10,22,23]: The elementary category of road vehicles embraces vehicles having all the same criterion characteristics, e.g., passenger vehicles with spark-ignition engines of displacement volume less than 1.4 dm 3 , compliant with Euro 3 emission standard and supplied with gasoline. Cumulated category of road vehicles embraces vehicles having not all the same criterion characteristics, as e.g., passenger vehicles with spark-ignition engines of displacement volume less than 1.4 dm 3 . All road vehicles (road fleet) represent the most cumulated category.
The elementary categories of vehicles included in this study correspond to the relevant categories in the COPERT 5 software. The software applies a disaggregation of the road fleet into the categories, according to the vehicle intended use, the ignition system of combustion engine and fuel used, including vehicles with hybrid electric-combustion drive [22,23]. Accordingly, this study concerns: passenger cars, light commercial vehicles (delivery vehicles), heavy duty trucks, urban buses, coaches, motorcycles, mopeds and micro-cars. The complete specification of vehicle categories is provided in the Supplementary Materials. Therefore, the national annual emission of pollutants is modeled as the superposition of annual emission from vehicles of the cumulative categories: where: j-cumulative category, K-total number of cumulative categories, n j -number of vehicles of cumulative category 'j', b AVxj -average value of specific distance emission of pollutant 'x' from vehicles of cumulative category 'j', L j -distance traveled by an imaginary vehicle of cumulative category 'j'. In models of pollutant emission from road vehicles, it is assumed that the intensity of pollutant emission associated with the use of motor vehicles with internal combustion engines is the sum of pollutant emission for the states of [7,9,22,23]: • internal combustion engine heated to a stable temperature; • internal combustion engine heating up; • fuel evaporation from the car fuel system.
In addition, the emission of particulates from sources other than combustion engines is taken into account, i.e., from the braking system, clutch and tires in contact with the road surface, and wear of other vehicle components.
The list of substances included in the EU pollutant emission inventories are shown in Table 1. For the purposes of the analysis carried out in this study, the number of substances was narrowed to those harmful to the health of living organisms, which are covered in vehicle type-approval regulations in the EU, i.e., carbon monoxide, non-methane volatile organic compounds, nitrogen oxides and particulate matter, with two particle size fractions distinguished, namely PM 10 and PM 2.5 (the latter were intentionally included, since virtually all particulate matter from the exhaust system of combustion engines belongs to the PM 2.5 fraction). The general rules for preparing data regarding road vehicles and their motion are outlined in the literature [8][9][10][15][16][17]. Data on the numbers of vehicles classified within cumulative categories in respect of the COPERT 5 software were elaborated, based on official data published by the Central Vehicle and Drivers Register. Annual distances travelled by road vehicles, by respective elementary category due to the technological level in terms of reducing pollutant emission, were adopted, after the model described in [18]. This model is based on the observation that newer vehicles with a higher technology level (defined by European emission standards) are used more intensively than older vehicles. Hence, to determine the annual mileage of vehicles belonging to the elementary categories, an increasing function is used, the argument of which is the quantity describing the subsequent stages of emission standards used in vehicle type-approval regulations. The values of this quantity are increasing, as newer stages of the regulations are implemented. Details, including the mathematical form of the model, are given in [18]. Data on consumption of different types of fuel in road transport come from Eurostat Database, which is fed by the Statistics Poland (GUS) [24]. Total fuel consumption was disaggregated into individual vehicle categories based on the COPERT 5 calculations, so that the mass of calculated fuel consumption is equal to that provided in the statistics. All detailed data used in the inventory of pollutant emission is published in official KOBiZE reports, including [15].
To evaluate changes in the quantities under consideration, the relative change in their values between the years 1990 and 2017 was assumed, according to the formula: where: X apr (1990)-value of the quantity 'X' in 1990, approximated by the linear function, X apr (2017)-value of the quantity 'X' in 2017, approximated by the linear function.
The authors decided to use the absolute difference related to the mean value, because it allows for a more objective assessment than the absolute difference related to one of the extreme values. More specifically, if the absolute difference was related to a smaller extreme value, a large result (relative change) would be obtained, while relating the absolute difference to a larger extreme value would give a small result, although the extreme values do not change. The formula proposed in the paper is unambiguous and independent of the choice of extreme value.
The national annual emission of pollutants, as the extensive-type characteristic, depends not only on the properties of road vehicles due to pollutant emission but, above all, on the number of vehicles and the intensity of their use. Therefore, while analyzing the results of the study on pollutant emission from road vehicles, the intensive characteristics of pollutant emission were assessed in order to estimate changes in the vehicle technical quality in terms of pollutant emission.
The average specific distance emission was adopted as the characteristic of pollutant emission [10] for the cumulative category of road vehicles in Poland between 1990Poland between -2017. This is the annual national pollutant emission related to the measure of the road vehicle activity, expressed as the distance travelled by road fleet over a year: where: b AVx -average specific distance emission of pollutant 'x' for cumulative category of road vehicles, E x -national annual emission of pollutant 'x' from the road fleet, L-distance travelled by the road fleet over a year. The distance travelled annually by road fleet is the sum of the products of numbers and annual distances travelled by road vehicles, by respective elementary categories 'i'. (6) where: N i -number of road vehicles of elementary category 'i', P i -annual distance travelled by road vehicles of elementary category 'i', K-number of elementary categories of road vehicles. The effects of the vehicle quality in terms of pollutant emission were also taken into account in the analyses. The quality of road vehicles concerning pollutant emission was estimated using data on the vehicles' structure at the level of elementary categories over the subsequent years. The estimation was made by comparing the measure of the activity of road vehicles by respective categories, due to pollutant emission, e.g., Euro 1 versus Euro 6 for passenger cars [25] and light commercial vehicles, and Euro I versus Euro VI for heavy duty trucks and urban buses [26]. The activity of road vehicles from individual categories in terms of pollutant emission is expressed by the distance travelled annually by aggregated vehicles from the respective category.

The Results of Pollutant Emission Inventory
Figures 1 and 2 illustrate the national annual emission of carbon monoxide, non-methane volatile organic compounds, nitrogen oxides, total suspended particles, particulate matter PM 10 , and particulate Sustainability 2020, 12, 5387 6 of 12 matter PM 2.5 . It should be noted that these results have already been published in the report [15], however, they are also included in this paper, due to the fact that they constitute the most important input for the analysis, the results of which are presented in the following sections. This certainly should facilitate assessment of trends in the quantities under consideration.
Sustainability 2020, 12, x FOR PEER REVIEW 6 of 13 important input for the analysis, the results of which are presented in the following sections. This certainly should facilitate assessment of trends in the quantities under consideration.  For all the pollutants examined, the annual emission varied over the subsequent years, however, there were differences between individual substances. Carbon monoxide and non-methane volatile organic compounds showed a downward trend. This is associated with a significant improvement in the properties of internal combustion engines in terms of emission of these substances-it is known that reducing emission of gaseous substances with oxygen-reducing properties is much easier and more effective than in the case of particulates and substances with oxidizing properties in an environment with high oxygen concentration [7]. Therefore, for nitrogen oxides and particle matter size fractions, there is a tendency for the national annual emissions to increase in subsequent years of inventory. Figure 3 shows the relative change in the national annual emission of pollutants.    For all the pollutants examined, the annual emission varied over the subsequent years, however, there were differences between individual substances. Carbon monoxide and non-methane volatile organic compounds showed a downward trend. This is associated with a significant improvement in the properties of internal combustion engines in terms of emission of these substances-it is known that reducing emission of gaseous substances with oxygen-reducing properties is much easier and more effective than in the case of particulates and substances with oxidizing properties in an environment with high oxygen concentration [7]. Therefore, for nitrogen oxides and particle matter size fractions, there is a tendency for the national annual emissions to increase in subsequent years of inventory. Figure 3 shows the relative change in the national annual emission of pollutants.  For all the pollutants examined, the annual emission varied over the subsequent years, however, there were differences between individual substances. Carbon monoxide and non-methane volatile organic compounds showed a downward trend. This is associated with a significant improvement in the properties of internal combustion engines in terms of emission of these substances-it is known that reducing emission of gaseous substances with oxygen-reducing properties is much easier and more effective than in the case of particulates and substances with oxidizing properties in an environment with high oxygen concentration [7]. Therefore, for nitrogen oxides and particle matter size fractions, there is a tendency for the national annual emissions to increase in subsequent years of inventory. Figure 3 shows the relative change in the national annual emission of pollutants.
The largest drop was noted for the national annual emission of carbon monoxide, while the emission of nitrogen oxides showed a small increase, and the emission of particulate matter size fractions showed the largest increase. In the latter case, much of the growth in the national annual emission of particulate matter is a consequence of the increase in the contribution of larger sized Sustainability 2020, 12, 5387 7 of 12 particulates from tires and brakes wear and, primarily, from road abrasion, while the emission of fraction PM 2.5 , which contains particles emitted by combustion engines, showed a minor increase.
Overall, the increase in the national annual emission of pollutants is a result of the dynamic development of motorization in Poland during the period from 1990, as is shown in Figures 4 and 5, but the numbers of road vehicles, distances travelled and fuel consumption have all grown most. The largest drop was noted for the national annual emission of carbon monoxide, while the emission of nitrogen oxides showed a small increase, and the emission of particulate matter size fractions showed the largest increase. In the latter case, much of the growth in the national annual emission of particulate matter is a consequence of the increase in the contribution of larger sized particulates from tires and brakes wear and, primarily, from road abrasion, while the emission of fraction PM2.5, which contains particles emitted by combustion engines, showed a minor increase.
Overall, the increase in the national annual emission of pollutants is a result of the dynamic development of motorization in Poland during the period from 1990, as is shown in Figures 4 and 5, but the numbers of road vehicles, distances travelled and fuel consumption have all grown most.     The largest drop was noted for the national annual emission of carbon monoxide, while the emission of nitrogen oxides showed a small increase, and the emission of particulate matter size fractions showed the largest increase. In the latter case, much of the growth in the national annual emission of particulate matter is a consequence of the increase in the contribution of larger sized particulates from tires and brakes wear and, primarily, from road abrasion, while the emission of fraction PM2.5, which contains particles emitted by combustion engines, showed a minor increase.
Overall, the increase in the national annual emission of pollutants is a result of the dynamic development of motorization in Poland during the period from 1990, as is shown in Figures 4 and 5, but the numbers of road vehicles, distances travelled and fuel consumption have all grown most.     Fuel consumption, shown in Figure 5, corresponds to the total energy consumption in road transport, from 285.73 PJ in 1990 to 864.75 PJ in 2017. The relative difference in fuel consumption for 1990 and 2017 is over 100%, and the relative increase in 2017 compared to 1990 is over 200%.
The drop in the national annual emission resulted mostly from the technological advancement in both the construction and operation of road vehicles, which helped to curb pollutant emission, in particular from combustion engines. Over almost two decades, mass-produced vehicles have introduced many systems that significantly reduce pollutant emissions and fuel consumption, such as advanced exhaust after treatment systems, start-stop, brake energy recuperation, variable valve actuation, gasoline direct injection, improved engine thermal management (e.g., for faster warm-up after cold start), advanced gearbox variations (increased number of gears, different gear ratios) and others [27,28]. The technologies facilitating the operation of vehicles have also been introduced, e.g., navigation systems with fuel-optimal route advise [29] or automated driving assistance systems supporting truck platooning [30]. Short-term changes in the national annual pollutant emissions (Figures 1 and 2), which are also reflected in the total fuel consumption (

Analysis of the Results of Pollutant Emission Inventory
Given the knowledge of the distance travelled by the vehicle fleet, it was possible to determine the average specific distance emission of pollutants and the average energy emission factor for the cumulative category of road vehicles. Figures 6 and 7 give the average specific distance emissions for the cumulative category of road vehicles in Poland between 1990 and 2017.  By far the strongest is the decrease in average road emissions of carbon monoxide and non-methane volatile organic compounds due to technical progress. Achieving a reduction in average road emission of nitrogen oxides is more difficult. For particulate matter, it is important to consider the different sources of origin, apart from the exhaust system of internal combustion engines. A particularly difficult problem is the reduction of particulate emissions from abrasion of the braking system components, as well as tires in contact with the road surface. In the first case, they are very fine particles, mostly with characteristic dimensions smaller than 1 µm, while in the second-with relatively large characteristic dimensions [22]. The relative change in the average specific distance emission of pollutants from road vehicles in 2017, as compared to 1990, is shown in Figure 8.  By far the strongest is the decrease in average road emissions of carbon monoxide and nonmethane volatile organic compounds due to technical progress. Achieving a reduction in average road emission of nitrogen oxides is more difficult. For particulate matter, it is important to consider the different sources of origin, apart from the exhaust system of internal combustion engines. A particularly difficult problem is the reduction of particulate emissions from abrasion of the braking system components, as well as tires in contact with the road surface. In the first case, they are very fine particles, mostly with characteristic dimensions smaller than 1 μm, while in the second-with relatively large characteristic dimensions [22].
The relative change in the average specific distance emission of pollutants from road vehicles in 2017, as compared to 1990, is shown in Figure 8. The tendency for the increase in the national annual emission of pollutants, i.e., characteristic with extensive properties, is possible as a result of the dynamic development of the automotive industry. On the other hand, average specific distance emissions of pollutants, i.e., characteristic with intensive properties, has a clear tendency to decrease over the period considered. Of course, according to the results presented previously, the strongest tendency to decrease is for the emission of carbon monoxide and non-methane volatile organic compounds. The main reason behind this tendency is the technological advancement of vehicles in terms of pollutant emission. Figure 9 provides a comparison of the road vehicle structure, expressed by distance travelled annually, according to vehicle environmental categories in the years 1990,1995,2000,2005,2015   The tendency for the increase in the national annual emission of pollutants, i.e., characteristic with extensive properties, is possible as a result of the dynamic development of the automotive industry. On the other hand, average specific distance emissions of pollutants, i.e., characteristic with intensive properties, has a clear tendency to decrease over the period considered. Of course, according to the results presented previously, the strongest tendency to decrease is for the emission of carbon monoxide and non-methane volatile organic compounds. The main reason behind this tendency is the technological advancement of vehicles in terms of pollutant emission. Figure 9 provides a comparison of the road vehicle structure, expressed by distance travelled annually, according to vehicle environmental categories in the years 1990,1995,2000,2005,2015 and 2017.
In Figure 9, a distinct improvement can be seen in the road vehicles in use, regarding pollutant emission from the cumulative category of road vehicles. Similar results can be observed for other cumulative categories of road vehicles, e.g., passenger cars, light commercial vehicles, heavy duty trucks and urban buses [15].
according to the results presented previously, the strongest tendency to decrease is for the emission of carbon monoxide and non-methane volatile organic compounds. The main reason behind this tendency is the technological advancement of vehicles in terms of pollutant emission. Figure 9 provides a comparison of the road vehicle structure, expressed by distance travelled annually, according to vehicle environmental categories in the years 1990,1995,2000,2005,2015 and 2017. In Figure 9, a distinct improvement can be seen in the road vehicles in use, regarding pollutant emission from the cumulative category of road vehicles. Similar results can be observed for other cumulative categories of road vehicles, e.g., passenger cars, light commercial vehicles, heavy duty trucks and urban buses [15].

Conclusions
Based on the results of the above analyses, the following conclusions can be formulated:

Conclusions
Based on the results of the above analyses, the following conclusions can be formulated:

1.
Between 1990 and 2017, the national annual emission from road vehicles in Poland has increased for some substances, first of all, for particulate matter size fraction and, to a lesser extent, for nitrogen oxides. This is mostly the consequence The relative reduction in national annual emission is the greatest for carbon monoxide-almost 120%-and for non-methane volatile organic compounds it is almost 85%. The relative increase in the national annual emission of nitrogen oxides is equal to about 25%, and the total particulate matter-almost 75%-including the PM 10 fraction-over 60%-and PM 2.5 -about 50%. The results of the relative reduction in the emission of the particle size fraction confirm the fact that reducing the emission of particles from sources other than the exhaust system of internal combustion engines is one of the most difficult technical tasks.

3.
Between 1990 and 2017, the average specific distance emission arising from road vehicles has decreased considerably. This clear improvement in the intensive characteristic of pollutant emission results from significant upgrading of the vehicle technology level in terms of reducing emission. In addition, it is known that the intensity of use of vehicles of higher ecological categories is much greater than of vehicles of lower ecological categories [18], which is confirmed by the data for inventory of pollutant emission from road transport in Poland, documented in the report [15].
Since the annual mileages of the newer generation cars overbalance those of older generation cars, the rise in the pollutant emission due to the dynamic development of motorization in Poland was considerably lower than could be expected, judging from the growth in numbers and intensity of use of road vehicles. However, according to authors, this is not yet the preferred situation. There is a need to establish and implement a system for eliminating old vehicles from road traffic and to implement an effective, in-depth control of the vehicle technological grade.
Supplementary Materials: The following are available online at http://www.mdpi.com/2071-1050/12/13/5387/s1, Vehicle categories included in the COPERT 5 software, Table S1: National annual emission of pollutants arising from road transport in Poland between 1990 and 2017, Table S2: Relative change in the national annual emission of pollutants arising from road transport in Poland in 2017 as compared to 1990, Table S3: Number of road vehicles in Poland between 1990 and 2017, Table S4: Distance travelled annually by the road fleet in Poland between 1990 and 2017, Table S5: Fuel mass consumption in road transport in Poland between 1990 and 2017: G-gasoline, DF-diesel fuel, NG-natural gas, LPG-liquefied petroleum gas, BD-biodiesel, BtOH-bio-ethanol, Table S6: Average specific distance emission of pollutants for cumulative category of road vehicles in Poland between 1990 and 2017, Table S7: Relative change in the average specific distance emission of pollutants from road transport in Poland in 2017 as compared to 1990,