Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Transport Policy journal homepage: www.elsevier.com/locate/tranpol
Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered E.A. Nanaki a,n, C.J. Koroneos b, G.A. Xydis c, D. Rovas b a
University of Western Macedonia, Department of Mechanical Engineering, Bakola and Sialvera, 50100 Kozani, Greece Laboratory of Heat Transfer and Environmental Engineering, Aristotle University of Thessaloniki, PO Box 483, 54124 Thessaloniki, Greece c Centre for Research and Technology Hellas, Institute for Research & Technology of Thessaly Technology Park of Thessaly, 1st Industrial Area, 38500 Volos, Greece b
art ic l e i nf o
Keywords: Climate change City public transportation Environmental assessment Athens
a b s t r a c t Greenhouse gases (GHGs) emitted by road transport vehicles as a direct result of fossil fuel combustion and other environmental pollutants released throughout the life cycle of petroleum based fuels, encourage a shift towards alternative transport fuels. Within this frame, an environmental assessment was performed so as to evaluate the environmental implications of alternative fuels (natural gas and biofuels) penetration in the city buses of the city of Athens. The results are evaluated in terms of CO2, CO, HC, PM and NOx emissions. The findings show that CO2 emissions are significantly reduced in CNG buses compared to diesel powered buses. CO2 emissions can also be reduced by 7.85% in B10 blends and 78.45% in B100 blends, compared to diesel. The environmental assessment can be considered as a basis so as to investigate the viability of replacement of petroleum- based diesel with natural gas and biofuels in city transport buses. Concepts for sustainable bus transportation can be incorporated using the methodology defined in this study, in order to promote a sustainable transportation system and mitigate the climate change. & 2014 Elsevier Ltd. All rights reserved.
1. Introduction Energy-related CO2 emissions, resulting from burning fossil fuels, represent the major part of recent human-made greenhouse gas emissions (GHG). Emissions from the transport sector are an important source of CO2 in many countries. Public transportation systems providing mobility and access to most activities play a crucial role to cities; nevertheless the shift to a low carbon public transportation system is challenging. In this context, cities have a key role to play in the global agenda for addressing the challenge of CO2 emissions mitigation. Especially in the case of European cities that face problems caused by transport and traffic, the challenge is to enhance mobility while at the same time reducing congestion and air pollution Despite the fact that improvements have been made in the energy efficiency of various transport modes and non-fossil fuels have been introduced, increased transport demand is outweighing these benefits (European Environment Energy (EEA), 2007).
n
Corresponding author. E-mail addresses:
[email protected] (E.A. Nanaki),
[email protected] (C.J. Koroneos),
[email protected] (G.A. Xydis),
[email protected] (D. Rovas).
In 2007, the transport sector accounted for 18% of total 2007 GHG, reaching a total of 24 million tones of CO2 equivalents (an increase of 33% on 1997 levels) (〈http://www.epp.eurostat.ec. europa.eu〉). Road transport is a significant source of air pollution in Greece, particularly within urban areas. To be more specific, road transport contributed to approximately 80% of these CO2 emissions highlighting the very real challenge in restructuring a sector which is intensive in energy demand, environmental impacts and continues to grow. The split between road transport oil in Greece from 1978 onwards is approximately 37% diesel and 63% gasoline, with the majority of the gasoline demand being for private car use (Papagiannaki and Diakoulaki, 2009). Based on our previous study (Koroneos and Nanaki, 2007) it is shown that a number of elements influenced the increased demand for private transportation. The increasing GDP, and therefore income of households, allowed householders to travel in more “luxury” benefiting from faster and more accessible private transportation as well as being a symbol of wealth. Additionally, distances travelled to work, shopping and leisure activities increased ensuring that total distance travelled by private cars measured in 1000 mio pkm also continued to increase. Nevertheless, Greece's economic crisis has lead an increasing number of motorists in urban areas such as Athens to resort to the capital's various forms of public transport as higher gasoline prices and
http://dx.doi.org/10.1016/j.tranpol.2014.04.001 0967-070X/& 2014 Elsevier Ltd. All rights reserved.
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
E.A. Nanaki et al. / Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
the unprecedented economic crisis dent the attraction of private vehicle use (〈http://archive.ekathimerini.com/4dcgi/_w_articles_ politics_0_28/05/2010_117332〉). Public transportation plays a vital role in the transportation system of an area and it also helps to minimize traffic congestion and other traffic-related externalities. Transportation problems are among the most pressing strategic development problems in many cities and are often considered as a major constraint for long-term urban development. In addition, transportation problems are very closely related to land development, economic structure, energy policies, and environmental quality. Since all citizens are either enjoying the transportation system or, and often at the same time, suffering from it, it is an important element of the urban quality of life. The public transportation system of Athens consists of buses, trolley buses, a subway system (metro) as well as tram. On the demand side, the daily traffic is of 2650,000 passengers. The average bus speed in the city centre is 7 km/h; whereas in areas outside the city centre the average speed increases to 13 km/h. The use of public transport in the whole metropolitan area of Athens in 2004 came up to 31.7%, whereas 68.3% represented private vehicles. As far as the main city is concerned 45% represented the use of public transport, whereas 55% represented the use of private vehicles (Website of European Metropolitan Transport Authorities, 2007). The strong gap between modal share in the main city and in the whole metropolitan area, where public transport accounts, in average, for 30% of motorized trips, illustrates one of the main challenges facing public transport authorities: developing public transport in the suburbs and the less dense parts of the metropolitan areas. The main objective of this study is to evaluate and analyse the environmental impacts from public transportation vehicles in urban areas and especially in the city of Athens and recognize possible routes for achieving the ambitious EU targets of 20–20– 20 on energy and climate. Furthermore, this study aims to determine the CO2 emissions reduction that could be achieved due to penetration of alternative transport fuels in urban bus fleet. The data used for this analysis were taken from the databases of Athens Urban Transport Organization.
2. Methodology The emission estimation methodology covers the exhaust emissions of CO, NOx, CO2, PM and HC for each vehicle technology of Athens's bus fleet. PM mass emissions in vehicle exhaust mainly fall in the PM2.5 size range. Therefore, all PM mass emission factors are assumed to correspond to PM2.5. The methodology used considers the fuel used by different vehicle categories and their emission standards. In this respect, the vehicle category of buses includes urban CNG buses and urban diesel buses according to emission-control legislation categories (EURO I, II, III, IV, V, VI). The technical data used take into account national variations. The variations may include parameters such as the fuel consumption, the composition of vehicle park, vehicle age, driving patterns, some fuel parameters and climatic conditions. Other variations which may exist, e.g. variations in vehicle maintenance, are not accounted for, because there is not enough data available to do so. The calculation is based on the following main types of input parameters: total fuel consumption, vehicle technology, vehicle park, driving condition, emission factors. The emission factors are stated in units of grammars per vehicle-kilometer for each vehicle technology. These average European emission factors are determined using typical values for driving speeds, ambient temperatures, highway-rural-urban mode mix, trip length, etc. (Ntziachristos and Samaras, 2009). Based on the above and in order to calculate the emissions of each
vehicle technology, the following equation was used: Ei; j ¼ Σ kðNj; k Mj; k EFi; j; kÞ
ð1Þ
where, j are the vehicle categories of diesel and CNG buses, k is the technology of each category (i.e. EURO I, EURO II, etc.), Nj, k is the number of vehicles in the city's under study bus fleet of category j and technology k, Mj, k represents the average annual distance driven per vehicle of category j and technology k, EFi, j, k represents the technology-specific emission factor of pollutant i for vehicle category j and technology k. From the above mentioned it is obvious that it is necessary to have data regarding the number of vehicles and the annual number of vehicle-km per technology. These vehicle-km data are then multiplied by the emission factors. Data concerning Athens's bus fleet (number of vehicles, categories, engine type as well as annual distance driven) were obtained from Athens Urban Transport Organization. The emissions factors used, are obtained from the studies of Ntziachristos and Samaras (2009), Nylund et al. (2004), Beer et al. (2000); Table 1 presents the emissions factors used for the diesel bus fleet; whereas Table 2 presents the emissions factors used for the CNG bus fleet.
3. Athens public transportation system Athens metropolitan area is the most populous area in Greece with 4.0 million people. The region covers an area of 1450 km2 encompassing 83 local authorities (municipalities) in 3 counties. Athens belongs to the Attica region and covers 35% of its surface area, with the Athens urban administrative area covering a total of 544 km2. Athens in terms of both surface area and population is densely populated (5882 people per square kilometre). The Athens Metropolitan area is surrounded by mountains from West to East and by the Aegean Sea from the South. Within the central urban area, the existence of several hills has an influence upon the transport in the city, causing local roads to have steep gradients. The Athens urban area has spread rapidly in recent decades and continues to expand, mainly to the East and the North. The transport infrastructure in Athens consists of a road network with a total length of 8000 km. The main road network covers 1826 km. The center of the city is the area bounded by the inner ring road (an area of 9.2 km2). There is also a (middle) ring road system surrounding an area of 111 km2. The road traffic in Athens—both in private and public modes- involves significant traffic delays and low traffic speeds. OASA is the shareholder in the Public Transport Operators that are members of the OASA Group: ETHEL S.A., (Thermal Buses), Table 1 Emissions factors for diesel bus fleet. Engine type
CO2 (g/km)
CO (grkm)
HC (g/km)
PM (g/km)
NOx (g/km)
EURO EURO EURO EURO EURO
1.397 1.386 1.351 1.343 1.330
1.50 1.35 1.00 0.95 0.74
0.3 0.2 0.15 0.09 0.06
0.45 0.2 0.18 0.06 0.01
16 14 9 6.38 3.83
I II III IV V
Table 2 Emissions factors for CNG bus fleet. Engine type
CO2 (g/km)
CO (g/km)
HC (g/km)
PM (g/km)
NOx (g/km)
EURO II EURO III
1.100 1.250
2.70 1.00
4.7 1.33
0.01 0.01
15 10
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
E.A. Nanaki et al. / Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
20 inter-municipal lines that connect the municipalities of the
ILPAP S.A. (Electric Buses) and ISAP S.A. (Athens—Piraeus Electric Railways). Public transportation is also provided by Public Transport Operators (Attiko Metro Operation Company (AMEL), TRAM and TRAINOSE—General Division of Suburban Transport based on contracts entered into between these operators and OASA. ILPAP operates an electric bus network of 22 lines that serve primarily the Athens and Piraeus city centres. The company owns and operates a fleet of 315 single trolley buses 12 m long and 51 articulated trolley buses 18 m long. ISAP S.A. operates the Electric Railway line that runs between Piraeus and Kifisia (metro line 1), serving 24 stations; whereas the total length of the network is 25.6 km. Attiko Metro Operation Company S.A. (ΑΜΕL S.A.) has been running Lines 2 and 3 of the Athens Metro since 2000, commissioning year of these two lines. The entire network is 51.1 km long and consists of 32 stations (including four that are in combined use with the Suburban Railway). Athens International Airport and the area of Messogia are also directly connected with the city center through 4 Metro Stations within a 22.1 km-long section of the Suburban Railway. Table 3 summarizes the annual passenger traffic during the period of 2005–2008 per public transport mode Athens Urban Transport Organization (2010). ETHEL S.A. operates the buses that serve the capital. Its transport network comprises of 319 bus lines and operates approximately 16.000 routes daily covering the capital in its entirety. ETHEL S.A's transportation network has a length of 8500 km. The fleet of buses consists of 2.151 vehicles of average age of 9 years, out of which 414 are powered by natural gas and 1.737 by diesel. Table 4 summarizes the characteristics of ETHELS. A.’s bus fleet. In 2010, the buses in operation carried out 12,815 routes per day. In addition, in 2010, ETHEL S.A. served 419 million transports for covering the needs of AMEL and ISAP. The bus line network is composed of the following lines:
4. Environmental assessment of Athens urban buses The main anthropogenic sources of air pollution in the metropolitan area of Athens can be attributed to industry (E40% of the total Greek industrial activity), transportation (E50% of the total automobile traffic) and heating. A large body of literature concerning the air pollution in Athens has been carried out. It includes inter alia the studies of Flassak and Moussiopoulos (1988), Asimakopoulos et al. (1992), Kallos et al. (1993), Pilinis et al. (1993), Ziomas (1998), Sotiropoulou et al. (2004, 2006). Dieselfuelled buses can be an important source of air pollutants. They can emit significant amounts of carbon dioxide (CO2), nitrogen oxides (NOx), particulate matter (PM2.5 and PM10), sulphur dioxide (SO2), sulphates (SO4), carbon monoxide (CO), and volatile organic compounds (VOCs). These air pollutants can contribute to the formation of smog and have been linked to a variety of acute and chronic health outcomes, including respiratory illnesses, heart disease, and premature death (Crump et al., 1991; Crump, 1999; Wichmann et al., 2000; Environmental Protection Agency, 2002). Natural gas is used widely as a combustion energy source, including power generation and industrial cogeneration; for these applications it is typically delivered at low to moderate pressure via utility pipeline. The use of natural gas, either as CNG (Compressed Natural Gas) or LNG (Liquefied Natural Gas) has been in the field of urban public transport the first alternative to diesel technology which has been implemented from the first half of the 90 s. Most natural gas vehicles utilize fuel cylinders containing natural gas that has been compressed at high pressure (200– 220 bar), reducing its volume by 99% compared to standard atmospheric conditions; this allows significantly greater driving range between fueling events. Natural gas is composed primarily of methane (typical composition: 87–96% methane, 1.5–5.1% ethane and 0.1–1.5% propane); it is commercially produced from oil fields or from natural gas fields.
with the centers of the peripheral municipalities. The radial lines connect the Athens and Piraeus city centers with the centers of the neighboring municipalities.
Table 3 Annual passenger traffic per public transport mode.
ETHEL ILPAP ISAP AMEL TRAM TRAINOSE Total
2006
2007
2008
393,611,762 84,231,072 124,038,181 172,197,626 12,922,259 2,905,457 789,906,358
413,292,350 88,442,626 135,821,809 177,363,555 14,488,146 2,741,216 832,149,702
423,509,574 91,815,297 148,725,181 185,719,257 18,729,130 3,345,974 871,844,413
421,080,000 92,200,000 149,050,000 193,100,000 19,800,000 3,500,000 878,730,000
Attica basin without crossing the Athens and Piraeus city centers. 123 local lines that operate within the limits of one or a group of neighboring municipalities and act as suppliers to the core lines. 19 express lines 7 school lines.
In 2009 ETHEL S.A. withdrew 255 urban diesel buses with obsolete engine technology (EURO I) and received 320 new diesel buses with new engine technology (EURO IV and EURO V) and SCR (selective catalytic reference) catalysts, in order to modernize our fleet and protect the environment.
40 core lines that connect the Athens and Piraeus city centers
2005
3
Table 4 Types of buses and their engine technology operating in Athens. Types of buses Fuel type diesel
EURO I
EURO II
MIDI 12 m 18 m Total
32 366 398
195 206 337 738
281
220
100 100
1737
Fuel type CNG
EURO I
EURO II
EURO III
EURO IV
EURO V
Grand total
294
120
294
120
MIDI 12 m 18 m Total
EURO III
EURO IV
EURO V
Grand total
220 281
414
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
E.A. Nanaki et al. / Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
While diesel engines use a lean combustion mixture and compression ignition, natural gas engines are spark-ignited and can use either a lean-burn or stoichiometric combustion mixture. The first generation of heavy-duty natural gas engines introduced in both developed and developing countries were lean burn engines based on diesel engine designs, with fuel injection systems borrowed from stationary natural gas engine technology. The earliest engines also employed simple open-loop fuel control systems and did not employ any after-treatment. The engine-out PM and NOx emission levels from a lean-burn CNG engine without any after-treatment system are low enough to outperform a conventional diesel engine (Euro III), or an advanced diesel engine with electronic control of fuel injection but without EGR or after treatment (Euro IV). Fig. 1 describes the development of emission regulations for European heavy-duty vehicles. The transition from Euro III to Euro IV class implies a remarkable tightening of emission values. The limit for particulate emissions (PM) decreases by 80% while the limit for nitrogen oxides (NOx) decreases more moderately, by 30%. The limit for particulate emissions is the same for Euro IV and V, resulting to a reduction of NOx by an additional 40%. The next
9 8
0.4
NOx g/kWh PM g/kWh
EURO I
7
EURO II
6 4
EURO III
0.2 0.15
3 2 0
0.3 0.25
5
1
0.35
EURO V
EURO IV
0.1 0.05
EURO VI
0
Fig. 1. Trends in European Emission Standards for heavy duty vehicles.
phase, Euro VI is already being discussed, and this class will enter into effect during the next decade. It is noted, that Euro I standards were introduced in 1992, followed by the introduction of Euro II regulations in 1996. In 1999, Directive 1999/96/EC introduced Euro III standards (2000), as well as Euro IV/V standards (2005/2008). In December 2007, the Commission published a proposal for Euro VI emission standards [COM(2007) 851]. Fig. 2 presents the kilometers driven and the fuel consumption of the diesel-powered bus fleet. The fuel consumption of EURO II engine is on average 2 times greater than this of EURO I engine technology and 7 times greater than this of EURO V. The 1737 diesel powered buses in the city of Athens, in 2009, carried out 91,302,660 km and consumed 51,271,350 l of diesel oil and emitted 125,467 t of CO2. In 2009 diesel buses in Athens with EURO II engine technology emitted 53,765 t of CO2 whereas EURO V engine technology buses emitted 6991 t of CO2 (Fig. 3). As the engine technology improves (EURO I to EURO V) the emitted CO2 per kilometer driven is reduced. It is obvious that as the engine technology improves (EURO Ι to EURO V) the emissions of NOx, PM, CO and HC resulting from the 1737 diesel buses are significantly reduced (Fig. 4). Looking at diesel vehicles, the variation of emissions is greater for Euro II vehicles than for the other engine technologies. The 414 CNG buses in Athens, in 2009, carried out 21,698 km and emitted 24,811 t of CO2. In 2009 CNG buses in Athens with EURO II engine technology emitted 16,950 t of CO2 whereas EURO III engine technology buses emitted 7991 t of CO2 (Fig. 5). CNG buses with EURO II engine technology emitted 72,422 t of HC whereas EURO III engine technology buses emitted 8.36 t of HC (Fig. 6). The high HC emissions for EURO II engine technology is attributed to the lean-burn technology. However, it should be noted that the HC emissions from CNG buses are more than 95% methane, which is neither toxic nor reactive. Nevertheless, methane is a strong greenhouse gas, and should be taken into account when calculating total greenhouse gas emissions. The PM
Fig. 2. Kilometers driven and fuel consumption from diesel bus fleet.
Fig. 3. CO2 emissions per diesel engine type in 2009.
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
E.A. Nanaki et al. / Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
5
Fig. 4. Annual pollutants emissions per diesel engine type in 2009.
CO2 20.000
tn/year
16.000 12.000 8.000 4.000 0 EURO II
EURO III
Fig. 5. CO2 emissions per CNG engine type in 2009.
Fig. 6. Annual pollutants emissions per CNG engine type in 2009.
emissions vary from 0154 t (Euro II) to practically zero (Euro III). All CNG vehicles perform well in these emissions, as do the diesel vehicles equipped with a properly functioning CRT filter. It is obvious that as the engine technology improves (EURO ΙI to EURO III) the emissions of CO, HC, PM and NOx resulting from the 414 CNG buses are significantly reduced (Fig. 6). CNGs show similar to higher CO emissions compared with the Diesel emissions. The use of CNG leads to an important decrease in NOx emissions compared to diesel buses. The mass of particles emitted by CNG engines is approximately 10 times lower than for diesel engines (EURO II). The highest CO values are found among Euro II vehicles, both diesel and CNG. Both NOx and PM emissions have a clear downward trend along with newer Euro emission standards, although certain bus models do not follow the general trend. Finally, as far as the CO2 emissions are concerned, it is noticed that CNGs emissions are lower compared with diesel powered buses (Fig. 7).
5. Biodiesel use in Athens urban buses Various alternative transport fuels such as biodiesel, ethanol, bioethanol, are already in use. Given that, in order to meet the
targets set within the Directive 2009/28/EC regarding the promotion of the use of energy from Renewable Energy Sources (RES) the elaboration of policies and measures targeting at the fulfillment of the “20–20–20” obligations and the acceleration of the Greek economy through “green” development and enhanced competitiveness of the private sector is required. The term biodiesel commonly refers to fatty acid methyl or ethyl esters made from vegetable oils or animal fats, whose properties are good enough to be used in diesel engines. The regulations limiting such properties are EN-14214 in Europe (UNE EN-14214, 2003) and (ASTM D)6751-03 in USA (ASTM D), although ethyl esters are not yet acknowledged as biodiesel in Europe (Council Directive, 2003). In this context, five alternative biodiesel blends that can be used in the urban buses of Athens are examined, so as to perform a comparative diesel and biodiesel analysis of air pollutants emissions. Emission calculations are based on 2009 data. The biodiesel blends, under study, consist of: Β10 (10% biodiesel and 90% diesel), B30 (30% biodiesel and 70% diesel), B50 (50% biodiesel and 50% diesel), B80 (80% biodiesel and 20% diesel) and B100 (100% biodiesel). The use of biodiesel blends in urban transport has both advantages and disadvantages. Figs. 8–10 are indicative not only of the environmental reductions that might be achieved with the
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
6
E.A. Nanaki et al. / Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Fig. 7. Annual pollutants emissions per CNG engine type in 2009.
Fig. 8. Annual pollutants emissions per different biodiesel blend and diesel.
Fig. 9. Annual CO2 emissions per each biodiesel blend and diesel.
use of different biodiesel mixes in the urban buses, but also of the environmental burdens. To be more specific, the HC, CO and PM emissions are reduced as the percentages of biodiesel in the biodiesel mixes are increased. For instance, HC emissions stemming from B100 are 67, 36% lower than the equivalent diesel emissions; whereas CO emissions stemming from B100 are 48, 11% lower than the equivalent diesel emissions and PM emissions coming from Β100 are 47, 19% lower compared with diesel emissions. On the other hand, NOx emissions are increased as the percentages of biodiesel in the biodiesel mixes are increased (10.29% increase in B100 blend compared to equivalent diesel emissions). Finally, as far as the CO2 emissions are concerned, it is noticed that these are reduced as the percentages of biodiesel in the biodiesel mixes are increased. CO2 emissions coming from
Β100 blend is 78.45% lower compared to equivalent diesel emissions; whereas CO2 emissions coming from B10 blend are 7.85% lower compared to equivalent diesel emissions. The abovementioned results of this study are in accordance with our previous study (Nanaki and Koroneos, 2009) where it was shown that biodiesel is beneficial with respect to the saving of fossil energy and to the greenhouse effect; nevertheless is detrimental regarding acidification, and euthrophication. 6. Discussion/conclusions The promotion of environmentally friendly and energy efficient vehicles, with the use of new technologies and cleaner fuels
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
E.A. Nanaki et al. / Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
7
Fig. 10. Air pollutant emissions per each biodiesel blend and diesel depicted in logarithmic scale.
constitutes a major policy component of the EU. EU directives, related to air emissions limits from internal combustion engines for vehicles from 1998 till now (“Euro” standards), have been transposed into the Greek legislation. In this context and given the ambitious EU targets of 20–20–20, the identification and investigation of climate change impact from the use of public transportation is of great significance. In this context, in the present study an environmental assessment of urban diesel and CNG bus fleet for the city of Athens, in 2009 was performed. Additionally, the environmental repercussions of the use of five different biodiesel blends in the bus fleet under study were also examined. The intense traffic problem that exists in the capital of Athens in conjunction with the targets set by EU necessitates the application of techniques that contribute to efficient traffic management and to the implementation of measures that upgrade the public transport services, improve the quality of life of citizens and increase the use of alternative transport fuels. The study indicates that penetration of CNG as well as biodiesel to the public transportation system of Athens could result in lower CO2 emissions. Lower emissions are of great significance for a sustainable urban transportation system. In order, to obtain lower emissions in CNG buses it is necessary to lean towards advanced engine technology by favoring injection systems. In addition, the replacement of CNG technology by CBG (biomethane) is considered to be sustainable low carbon solution that could be further investigated. Despite the environmental benefits from the use of CNG technology in the bus fleet of Athens, major barriers are the infrastructure issues. The infrastructure of CNG fuelling stations, gas upgrading plants and gas injection exists or is expanding in a few countries like Austria, Germany, Italy, Netherlands, Sweden and Switzerland. In other countries, refueling infrastructure is rudimentary and has to be extended or still created. The development of methane vehicles is strongly hampered by very high investment costs that are required for the build-up of the needed methane refueling infrastructure. The main driver behind investments in the methane refueling infrastructure has mostly been the natural gas industry, especially when it comes to the promotion and construction of public refueling opportunities for passenger cars and vans. The expansion of private refueling facilities for commercial fleets of light and heavy duty and public transport companies of urban buses and trucks mainly results from local initiatives between public authorities and industry. The disparities in the level of development for using methane in transport in Europe are due to specific national investment strategies and to a certain extent also to the availability of economic resources. In addition to this, investments for the development of infrastructure take time, which is even more evident in the case of CNG stations
where investments are at least five times higher than for conventional liquid fuels. More established NGV (Natural Gas Vehicle) countries needed more than 15 years to develop the infrastructure of today. It is therefore clear that countries like Greece, that is now starting the construction of methane refueling stations, will require time, at least until 2025 or beyond, to guarantee adequate refueling. Political support and binding targets, incentives and subsidy schemes would certainly speed up the build-up of infrastructure. A coherent public policy will also be crucial (Report of the European Expert Group on Future Transport Fuels, 2011). To be more specific, improvement of the legislative framework and establishment of CNG standards in conjunction with training of technicians (for converting of vehicles) as well as with the cooperation of the whole chain of the fuel sector in Greece for the promotion of CNG (Government/Vehicle Importers/Vehicle Service Stations/Existing Fuel Station Grids) are necessary steps for CNG deployment (Website of DEPA). Furthermore, the use of adapted after- treatment can decrease exhaust emission pollutants level, produced by diesel-powered bus. In that case, some trap technologies can be associated with adapted Diesel—fuel formulations, constant filter maintenance, etc. As it has been shown in previous studies, the most effective way to reduce regulated emissions is to replace old vehicles with new ones; whereas the most effective way to cut GHG emissions is to switch from fossil fuels to efficient biofuels (Nylund et al., 2012). The use of biodiesel in the public transportation system of Athens can be beneficial; nevertheless the use of most advanced liquid biofuel HVO (Hydro treated Vegetable Oil) can reduce significantly NOx emissions. It is noted that a very cost-effective and rapid way to reduce emissions is to use HVO in Euro I and Euro II engines since in those the reduction of emissions in g/km is the highest and it can take place in all Euro I and Euro II vehicles immediately. HVO can be used also in the most modern diesel engines and after treatment systems where high FAME concentrations may cause technical difficulties (Nylund et al., 2011). Biodiesel has the potential to curb greenhouse gas emissions in the transportation sector as long as it satisfies all sustainability criteria as established by the EU legislation in force, including the biodiesel blends present in the market as well as future advanced types that might be developed. Higher blends of biodiesel might be needed to fulfil the climate change targets. Only comparatively marginal alterations to the distribution system are needed. It is noted that no adaptation in consumer behavior is needed (driving range, refueling habits, look and feel of the car). The results of the present study can be used as an input to the strategic decision- making process for future transport energy policy and also to identify key areas of interest for further
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
E.A. Nanaki et al. / Transport Policy ∎ (∎∎∎∎) ∎∎∎–∎∎∎
8
technology research and development of the public transport system in Athens. A transportation public system, which fosters a positive attitude towards alternative fuels and new power train concepts using captive fleets as forerunners, is a significant parameter for a sustainable transportation system, which aims at the improvement of public transportation energy efficiency, improvement of the quality of the offered public transport services making it by this way more attractive to passengers and to environmental sustainability. References ASTM D 6751-03. Standard Specification for Biodiesel (B100) Blend Stock for Distillate Fuels, 2008. 〈http://www.epp.eurostat.ec.europa.eu〉. Asimakopoulos, D., Deligiorgi, D., Drakopoulos, C., Helmis, C., Kokkori, K., Lalas, D., Sikiotis, D., Varotsos, C., 1992. An experimental study of nighttime air-pollutant transport over complex terrain in Athens. Atmos. Environ. Part B 26, 59–71. Athens Urban Transport Organization: 〈www.oasa.gr〉. 〈http://archive.ekathimerini.com/4dcgi/_w_articles_politics_0_28/05/2010_117332〉 (accessed: September 2013). Athens Urban Transport Organization, 2010. Annual Report for the Period 1.1.200831.12.2008. Beer, T., Grant, T., Morgan, G., Lapszewicz, J, Anyon, P., Edwards, J., Nelson, P., Watson, H., Williams., D., 2000. Life—cycle Emissions Analysis of Alternative Fuels for Heavy Vehicles. Australian Greenhouse Office. Council Directive, 2003. 2003/30/EC of the European Parliament and of the Council. The Promotion of the use of Biofuels or other Renewable Fuels for Transport. Crump, K.S., 1999. Lung cancer mortality and diesel exhaust: reanalysis of a retrospective cohort Study of U.S. railroad workers. Inhalation Toxicol. 11, 1–17. Crump, K.S., Lampert, T., Chen, C., 1991. Assessment of Risk from Exposure to Diesel Engine Emissions, 68-02-4601-56; Prepared for U.S. Environmental Protection Agency, Office of Health Assessment, Washington, DC, by Clement International Corporation. Environmental Protection Agency, 2002. EPA, Health Assessment Document for Diesel Engine Exhaust, National Center for Environmental Assessment, Office of Research and Development, Washington DC. European Environment Energy (EEA), 2007. Climate for a Transport Change, TERM: Indicators Tracking Transport and Environment in the European Union, No 1/ 2008, Copenhagen. Flassak, Th., Moussiopoulos, N., 1988. An application of an efficient non- hydrostatic mesoscale model. Boundary Layer Meteorol. 41, 135–147.
Kallos, G., Kassomenos, P., Pielke, R.A., 1993. Synoptic and mesoscale weather conditions during air pollution episodes in Athens Greece. Boundary Layer Meteorol. 62, 163–184. Koroneos, C., Nanaki, E., 2007. Environmental assessment of the Greek transport sector. Energy Policy 35, 5422–5432. Nanaki, E.A., Koroneos, C.J., 2009. Comparative LCA of the use of biodiesel, diesel and gasoline for transportation. In: Proceedings of the First International Exergy, Life Cycle Assessment and Sustainability Workshop & Symposium (ELCAS) (C.J. Koroneos and A. Dompros, Eds.), Nisyros Island. Ntziachristos, L., Samaras, Z., 2009. EMEP/EEA Air Pollutant Emission Inventory Guidebook, updated June 2010. Nylund, N-O, Erkkilä, K., Lappi, M., Ikonen, M., M, 2004. Transit Bus Emission Study: Comparison of Emissions from Diesel and Natural Gas Buses; VTT Technical Research Centre of Finland; Research Report. Project 3/P5150/04. Nylund, N-O, et.al. 2011. Optimized Usage of NExBTL Renewable Diesel Fuel. VTT Research Notes 2604. Nylund, N-O, et al., 2012. Fuel and technology alternatives for buses. VTT Technol. 46. Papagiannaki, K., Diakoulaki, D., 2009. Decomposition analysis of CO2 emissions from passenger cars: the cases of Greece and Denmark. Energy Policy 37, 3259–3267. Pilinis, C., Kassomenos, P., Kallos, G., 1993. Modeling of photochemical pollution in Athens, Greece application of the RAMS-CALGRID modeling system. Atmos. Environ. Part B 27, 353–370. Report of the Europena Expert Group on Future Transport Fuels, 2011. Infrastructure for Alternative Fuels. Sotiropoulou, R.E.P., Tagaris, E., Pilinis, C., Andronopoulos, S., Sfetsos, A., Bartzis, J.G., 2004. The bond project: biogenic aerosols and air quality in Athens and Marseille Greater Areas. J. Geophys. Res. 109, D05205, http://dx.doi.org/ 10.1029/2003JD003955. Sotiropoulou, R.E.P., Tagaris, E., Pilinis, C., Antilla, T., Kulmala, M., 2006. Modeling new particle formation during air pollution episodes: impacts on aerosol and cloud condensation nuclei. Aerosol Sci. Technol. 40, 557–572. UNE EN-14214, 2003. Fatty Acid Methyl Esters (FAME) for Diesel Engines— Requirements and Test Methods. Website of DEPA: 〈http://www.depa.gr〉. Website of European Metropolitan Transport Authorities, 2007. 〈www.emta.com〉. Wichmann, H.E., Spix, C., Tuch, T., Wö lke, G., Peters, A., Heinrich, J., Kreyling, W.G., Heyder, J., 2000. “Daily Mortality and Fine and Ultrafine Particles in Erfurt, Germany—Part I, Role of Particle Number and Particle Mass,” HEI Research Report No. 98, Health Effects Institute: Cambridge, MA. Ziomas, I.C., 1998. The Mediterranean campaign of photochemical tracers- transport and chemical evolution (MEDCAPHOT-TRACE): an outline. Atmos. Environ. 32 (12), 2045–2053.
Please cite this article as: Nanaki, E.A., et al., Comparative environmental assessment of Athens urban buses—Diesel, CNG and biofuel powered. Transport Policy (2014), http://dx.doi.org/10.1016/j.tranpol.2014.04.001i
