Urban Air Pollutant from Motor Vehicle Emissions in Kuala Lumpur, Malaysia

The increasing amount of motor vehicles that emit pollutants are contributing significantly to urban air pollution, be it in industrial or developing countries. This study investigates the emission of particulate matter (PM10) from exhaust and nonexhaust sources and gaseous pollutants, such as carbon monoxide (CO) and nitrogen oxide (NOx) from several different classes of motor vehicles in the tropical city of Kuala Lumpur. Air pollutants from fuel consumption were obtained from emission factors, while non-exhaust particulate matter was estimated from the United States Environmental Protection Agency (U.S. EPA) Compilation of Air Pollutant Emissions Factors (AP-42). The total PM10 emissions from all classes of motor vehicles estimated from the tail-pipe exhaust was 1,029,883 kg, while non-exhaust sources were 1,573,539 kg. Emissions of PM10 from newly registered private cars was the most dominant at 214,427 kg, followed by emissions from motorcycles at 118,582 kg in 2014. Private cars also contributed 14,605 kg of CO and 5,726 kg of NOx in 2014, compared with 9,830 kg of CO and 3,854 kg of NOx in 2010. Comparison with other Organisation for Economic Co-operation and Development (OECD) countries shows that the total emissions for PM10 and NOx were lower in Malaysia than in most countries, but the CO emissions here were higher than in Asian countries such as Japan and Korea, as well as in other European countries. Various strategies and policies should be implemented by the local authorities and government agencies to reduce emissions from the transportation sector in urban areas to improve the quality of the urban environment, human health, and the urban community.


INTRODUCTION
The transportation sector is a major source of traffic pollution in the city center. High levels of economic growth, rapid urbanization, increasing disposable income, a variety of social and recreational activities, increasing private vehicles, and the distribution of dissimilar materials and resources have directly increased the demand for the transport sector and leading to a deteriorating urban air quality (Saboori et al., 2014;Shahbaz et al., 2015). These increasing emissions from the transportation sector are contributing factors to domestic air pollution, global climate change, human health problems, and ground-level ozone formation at both regional and national scales (Saija and Romano, 2002;Azam et al., 2016).
Generally, the major sources of urban air pollution to individual health are particulate matter (PM) and nitrogen dioxide (NO2) through emission from vehicle exhaust (Ghaffarpasand et al., 2020). In 2016, on-road vehicles accounted for about 39% and 20% of total NOx and carbon monoxide (CO) emissions in the European Union (EU), and it is found those passenger vehicles are the major cause of NOx and CO emissions from road transportation (EEA, 2018). Meanwhile, motor vehicles using diesel fuel have been identified as a major contributor to high NOx emissions in Europe (Anttila et al., 2011;Henschel et al., 2015) beside CO and total hydrocarbons (THC) .

Fuel Consumption and Motor Vehicle Emissions
The transportation sector consumes about 48 million barrels of oil per day compared to the current global total of 93 million barrels of oil a day from more than 1.5 billion motor vehicles (EIA, 2014). Fuel consumption is defined as the amount of fuel consumed per unit distance and expressed in litres/100 km. The lower value of fuel consumption by vehicles has shown that high savings occur (Mathew, 2014). The higher octane petrol is cooler and significantly produces lower nitrogen oxide (NOx) release levels (Al-Arkawazi, 2019). Cheah et al. (2008) investigated that fuel consumption and emission of pollutants from motor vehicles recorded a reduction from 11.2 litres/100 kilometres in 2007 to 5.6 litres/100 km, while the sales-weighted average fuel economy increased from 21 miles per gallon (mpg) in 2007 to 42 mpg by 2035. The International Energy Agency (IEA) specified that energy consumption from the global transport sector and greenhouse gas emissions are expected to increase by approximately 50% by 2030 and 80% by 2050 . Higher fuel consumption in motor vehicles was detected at urban signalised intersections due to the frequent changing of vehicle modes of deceleration, acceleration, and stopping .
In Malaysia, private cars, motorcycles, light, and heavy vehicles are major contributors to deterioration in air quality, especially in urban areas. The total number of newly registered motor vehicles from 2004 to 2017 was 286,771,902 units, comprising five classes: passenger cars, motorcycles, vans/lorries, and taxis/buses (DOE, 2017). Motorcycles and passenger cars are the dominant classes of motor vehicles, with 6,572,366 units in 2004 that increased by 35% to 11,989,591 units in 201511,989,591 units in (DOE, 2015. The same situation was shown for passenger cars, with 5,911,752 units in 2004cars, with 5,911,752 units in that grew by 35% to 13,173,030 units in 2017cars, with 5,911,752 units in (DOE, 2015cars, with 5,911,752 units in , 2017. Motor vehicles and traffic emissions are directly related to the fuel consumption caused by an incomplete combustion process in the engine system. Fuel consumption from the transport sector in Malaysia showed an upward annual trend, as evidence by the 5,386 kilotonnes of oil equivalent (ktoe) in 1998 that rapidly increased to 23,435 ktoe in 2015 (Energy Commission Malaysia, 2014). Combustion of fossil fuels from petrol, fuel oil, and natural gas in the internal combustion engine of a motor vehicle releases air pollutants, such as carbon monoxide (CO), sulphur dioxide (SO 2), oxides of nitrogen (NOx), non-methane volatile organic compounds (NMVOC), and particulate matter (PM) (Ong et al., 2011;Azam et al., 2016). In addition, transport activities from private and goods vehicles emit about 20% of greenhouse gases (World Bank, 2014;Alshehrya and Belloumi, 2017).
In Malaysia, energy consumption directly relates to the transport sector, foreign direct investment, and pollutant emissions that resulted from positive economic growth (Department of Statistics Malaysia, 2011). Consequently, higher fossil fuel consumption in Malaysia resulted in a 6.7% increase in annual average growth from the transportation sector from 1971 to 2008, which is comparable to Thailand at 6.6% and Indonesia at 6.3% (Ghosh, 2010). The increased consumption of fossil fuels in Malaysia from 1960 to 2002 resulted from the increasing motor vehicle ownership, with an average of 6.7% for 1,000 persons (Dargay et al., 2007).
The energy use from the transportation sector from fossil fuels was estimated at 50% in Malaysia, which is the highest in ASEAN (Chandran and Foon, 2013). Traffic emissions are also influenced by rapid urbanisation that impacts the population, economic growth, and activity services, particularly in the city centres. According to the 10th Malaysia Plan, the rate of urbanisation in Malaysia has increased from 25% in 1960 to 65% in 2005, with the expected increase of 75% of the population residing in the Klang Valley conurbation by 2020 (Kuala Lumpur City Hall, 2004).
Thus, the objective of this study is to calculate the emissions of particulate matter from the exhaust and nonexhaust and gaseous pollutants from the fuel consumption of the vehicle class passenger cars, motorcycles, buses, and goods transport from 2010 to 2014 in the metropolitan city of Kuala Lumpur. This study utilizes the top-down approach based on fuel consumption for CO and NO x, and the bottomup approach (vehicle kilometre travelled (VKT) and number of vehicles) for particulates. The CO and NOx emissions from motor vehicle exhausts are calculated based on fuel consumption (Masjuki et al., 2004;Kakouei et al., 2012), while the particulates include the exhaust PM 10 and nonexhaust source from paved roads. The different approach for CO and NOx are used, as they are gaseous pollutants from motor vehicles through the fuel combustion process as petrol and diesel directly affect the levels of CO and NOx released. For PM10 emissions from motor vehicle exhaust, it is estimated using VKT and number of vehicles (EIA, 2005) because the movement the motor vehicles or driving patterns directly influence the emission of PM 10 (Rostampour, 2010). Thus, VKT is affected by the flow of traffic and traffic congestion. Furthermore, the number of vehicles also caused serious traffic congestion through different driving patterns. The CO, NOx, and PM10 emissions will be compared to the Organisation for Economic Co-operation and Development (OECD) countries to gauge the rank of an environmental indicator of urban Kuala Lumpur that represents a developing country. The identification of the vehicle class that contributes the most emissions to the atmosphere in Kuala Lumpur may help policymakers to adopt a strategy to reduce air pollutants and the impacts of climate change on the city.

Study Area: Urban Kuala Lumpur
Kuala Lumpur (KL) is the federal capital of Malaysia and is a prominent and sophisticated city in Southeast Asia, acting as a centre of commercial and industrial activities (Ling et al., 2010;Teriman et al., 2010;Jamhari et al., 2014). Kuala Lumpur covers an area of 24,221 hectares and is located on the west coast of Peninsular Malaysia (Fig. 1). It has a total population of 1,627,172 inhabitants and a density of over 6,800 persons per square kilometre (Teriman et al., 2010). More than 60% of Malaysians live in urban areas in 2010 and it is predicted to increase to 75% in 2020 (Shuid, 2004).
Kuala Lumpur city is situated in the Klang Valley or Kuala Lumpur Conurbation (KLC). Under the Kuala Lumpur Structure Plan (2004Plan ( -2020 and the Kuala Lumpur City Plan, it was divided into six strategic planning zones for the purposes of city planning (Architects and Urban Planners Malaysia, 2006) consisting the City Centre, Sentul-Menjalara, Wangsa Maju-Maluri, Damansara-Penchala, Bukit Jalil-Seputeh, and Bandar Tun Razak-Sungai Besi (Ling et al., 2012). Road transport represents 84% of the city's mobility, with private cars accounting for 57% of all motorised trips in Kuala Lumpur (Kuala Lumpur City Hall, 2004). Currently, Kuala Lumpur has a total of 1,213 kilometres of road length (Teriman et al., 2010). According to a report from the Public Work Department of Malaysia (2014), the overall road network in Kuala Lumpur, covering Kuala Lumpur-Kuala Selangor, Kuala Lumpur-Ipoh, Kuala Lumpur-Seremban Expressway, and Kuala Lumpur-Damansara, with a total length of 1,531.20 km, had a traffic volume recorded at 1,083,320 units for a 16-hour duration in 2010.
Newly annual registered motor vehicle data for Kuala Lumpur was provided by the Department of Road Transport Malaysia (MOT) at the Wangsa Maju branch. Data were classified to different categories and according to the fuel consumption of private cars and motorcycles (petrol), and buses and goods vehicles using diesel from the year 2010 to 2014. The exhaust emissions of CO and NOx are obtained from their fuel consumption, while particulate matter emission is estimated based on Baidya and Borken-Kleefeld (2009). The non-exhaust particulate matter from paved roads is calculated using the formula from the emission factors provided by the United States Environmental Protection Agency (U.S. EPA) AP-42 (U.S. EPA, 2011).

Fuel Consumption
Fuel consumption for each vehicle class was analysed using Eq. (1) below by Kakouei et al. (2012): where: Fc = Fuel consumption in a day (diesel or petrol) in litres; A c = Average fuel consumption by each type of vehicle per kilometre (L km -1 ); V = Number of each type of vehicle; and Rd = Amount of running per day by the vehicle (km). * The value of Rd is the number of vehicle trips (km) per day and is estimated from the survey answered from 200 residents in Kuala Lumpur (Mohd Shafie, 2019). The small value of Rd is because it involves the average short-range distance performed by the residents of Kuala Lumpur. The average daily distance travelled is 14 km. The emissions of CO and NOx were next calculated from fuel consumption using Eq. (2) (Masjuki et al., 2004): where: TMi = Total emission in year i (kg); ES = Energy use in year of fuel type (ktoe); FE n/p = Emission per unit energy of fuel type n (kg GJ -1 ); CF = Conversion factor. * The conversion factor (CF) used in this study is 1 toe = 41.86 GJ (UN, 1991;IEA, 2002;EIA, 2004

Particulate Matter Emissions
Particulate matter emissions from road vehicles comprise emissions from tailpipe exhaust and non-exhaust emissions such as brake, tires and clutch, and re-suspension of dust (Thorpe and Harrison, 2008). Particulate emissions from the surface of paved roads via the movement of motor vehicles are estimated by using the following equation from U.S. EPA AP-42 (U.S. EPA, 2011). Default values used in this analysis: k = 4.6, sL= 0.62 g m -2 , W = 3.4 tonnes (U.S. EPA, 2011).
where: E = Particulate emission factor (units match the units of k); k = Particle size multiplier for particle size range and units of interest; sL = Road surface silt loading (grams per square meter) (g m -2 ); and W = Average weight (tonnes) of vehicles traveling the road. Meanwhile, particulate matter emission from vehicle exhaust is based on mainly the fuel consumption (petrol and diesel), vehicle kilometre travelled (VKT), and emission factors. VKT is derived from Eq. (4) (EIA, 2005) and emission factor using Eq. (5).

Motor Vehicles in Kuala Lumpur
The total number of new motor vehicles registered from 2010 to 2014 consists of private cars, motorcycles, goods vehicles, and buses. The annual trend showed a continuous increase of 3.71% per year from 3,161,741 units in 2010 to 3,812,460 units in 2014 (Fig. 2). The highest numbers of vehicle classes are the private cars and motorcycles, which recorded 10,906,065 units (an increase of 62.37%) in 2014 and 6,030,752 units in 2010. This is in contrast to a lower number of goods vehicle at 498,837 units or 2.85% increase, while buses showed a lower quantity of 48,113 units or 0.27% of the total vehicles.
The total newly registration motor vehicles in Kuala Lumpur significantly showed annual averaged VKT for private cars is highest year by year from 26,259,715 km in 2010 to 31,919,321 km in 2014 compared to other vehicles classes. In addition, motorcycles recorded an increasing annual averaged VKT of 14,658,117 km and reached 17,651,935 km beside 1,307,720 km to 1,371,397 km for goods transport during the study period (Table 4).
The total pollutants emitted by private cars, motorcycles, buses, and goods vehicles from 2010 to 2014 for PM 10 (exhaust and non-exhaust), CO, and NOx are 2,603,422 kg, 80,875 kg, and 33,437 kg, respectively (Fig. 1). The total PM 10 emissions from exhaust is 1,029,883 kg and 1,573,539 kg from non-exhaust from 2010 to 2014. Overall, non-exhaust PM10 emissions from private cars and motorcycles emit the highest total of PM10 in 2014 at 214,427 kg and 118,582 kg, respectively. This is followed by tailpipe PM10 emission of 142,952 kg from private cars and 79,055 kg by motorcycles in 2014. Meanwhile, goods vehicles released 9,212 kg of PM10 in 2014. Buses also showed similar conditions but in minimal quantities from 864 kg in 2010 to 869 kg in 2014.

Transport Emissions in Kuala Lumpur
The CO emission from private cars was high, which was about 14,605 kg in 2014 in contrast to 9,830 kg in 2010. Additionally, goods vehicles and buses produced CO emissions of 72 kg and 69 kg in 2010, respectively, from which the numbers had slightly increased to 79 kg and 70 kg, respectively, in 2014. Similarly, NOx also accounted for the   (Table 5).
The highest PM10 emissions in Kuala Lumpur were from private cars and motorcycles during peak hours at 0700 to 0900 and at around 1700 hr to 2000 hr in the morning and evening, respectively (Azhari et al., 2018). This significantly increased the emissions due to the minimum speed limits of the vehicles and stop-and-go vehicle in traffic lights (Madireddy et al., 2011). Individual attitude and driving patterns, characteristics and types of vehicles, the physical aspect of road surface, average vehicle speed, as well as traffic conditions all affect the rate of emissions (Barth and Boriboonsomsin, 2009).
Generally, CO and NOx pollutants are emitted from fuel consumption in vehicle movement process, with diesel fuel producing higher emissions than petrol. However, the emission from petrol fuel is also attributed by the high number of motor vehicles compared with goods vehicles that consume diesel in Kuala Lumpur. Vehicles of less than five years with newer engine technology can reduce CO and NOx emissions by 71% and 10%, respectively (Clark et al., 2002).
Taxi was excluded in this study, where it cumulatively accounted for only 335 units in 2010, which increased to 336 units in 2014, through the use of natural gas (natural gas vehicles or NGV) in Kuala Lumpur. Furthermore, the rapid growth of mobile technology and smartphone applications significantly led various companies to develop relationships with consumers through mobile applications (Zhang, 2017;Chin and Lai, 2018). For example, MyTeksi was introduced in Kuala Lumpur and was subsequently branded as GrabTaxi in 2011. Then, GrabCar was officially launched in Malaysia following the increasing use of GrabCar due to usage of safety, time efficiency, and convenience to passengers and drivers alike in 2014 (Jayaraj et al., 2019).
In Malaysia, Grab was launched in 2012 as a third-party taxi e-hailing mobile application (Lin and Dula, 2016). Report from The Land Public Transport Commission (SPAD) summarized that 80% of the public are more likely to use Uber and GrabCar services due to high accessibility factors (New Straits Times, 2017). Today, Grab is the best platform for driving individual day trips mostly for drivers and passengers to choose and use the Grab application in Southeast Asia. Therefore, using taxis for mobility is deemed impractical and not the popular choice for Kuala Lumpur residents.
The Organisation for Economic Co-operation and Development (OECD, 2019) also released information on the road transport emissions of CO, NOx, and PM10 (Table 6). The list of countries included for comparison are Germany, which represents an industrialised European nation; Chile and New Zealand, which represent the countries in the Southern Hemisphere; while Japan and Korea represent the Asian Pacific countries. No information is available for ASEAN countries. Germany recorded the high emissions of PM10, NOx, and CO in 2010 but displayed a decreasing trend in 2014. Asian countries, such as Korea, also showed a similar     (DOE, 2011(DOE, , 2015. The increasing trend of CO and NOx emissions is mainly due to the increase in total motor vehicles, which mostly consume fossil fuel. Malaysia should adopt more green transport initiatives since the trend of emissions of pollutants from the transportation sector in Malaysia is on the increase compared to other OEDC countries. Currently, approximately 90 percent of vehicles are fossil-fueled, hence the low number of environmental-friendly electric vehicles of less than 6,000 units on Malaysia roads (Md Khalili, 2019). China leads the market for electric vehicles with 2.3 million in 2018, followed by 1.3 million in Europe (IEA, 2019). In the US and Europe, mobile source emission controls such as exhaust after-treatment technologies for diesel and petrol vehicles that meet strict regulations have reduced emission (Winkler et al., 2018). Stricter Euro 6 emission limits for petrol and diesel were imposed in Europe since 2015 (The Automobile Association, 2020). Policies in some OECD countries to reduce emissions include a zero-emissions vehicles (ZEVs) mandate in Canada by 2030, while in Korea initiatives include national subsidies for low-carbon vehicle purchases in 2018, abatement and subsidies on vehicle taxes, decreased road tolls and municipal parking rates (IEA, 2019).
Some of the reasons why the usage of electric cars is in low demand is due to the limited options of cars available, the expensive price tag of the cars from the tax of imported vehicles imposed by the Malaysia government, the lack of public awareness on the importance of green technology and environmental-friendly modes of transport (Bernama, 2019).
In order to achieve a green technology nation, the government needs to implement comprehensive initiatives to achieve these targets such as those outlined in the National Electric Mobility Blueprint (2015-2030) (GreenTech, 2015). By 2030, the government aspires to attain 100,000 electric cars; 100,000 electric motorcycles and 2,000 electric buses on Malaysian roads, as well as 125,000 charging stations (Bernama, 2019).
Malaysia should follow the industrialised OECD countries that had successfully reduced GHG and air pollutants from the road transport over the past ten years. Incentives for tax credits for those using green technologies, such as electric vehicles, should encourage more consumers to use affordable green vehicles that consume less fuel. The Malaysian Green Technology Corporation (MTDC) was charged to install 3,000 charging sites in government buildings, petrol stations, and shopping malls by 2018 to encourage for e-mobility of electric cars (Aswan, 2019), of which there were only 5,403 efficiency vehicle (EV) cars in March 2019. This is still below the target set by the National Electric Mobility Blueprint (2015) projection of 125,000 charging stations by 2030, where power supply for customers remains a problem (Zainuddin, 2019). Incentives were also given on energy efficiency vehicles (EEVI) and plug in hybrid efficiency vehicles (PHEV) as was implemented successfully in other Asian countries (China, Japan, India), Europe, and the USA. However, the growth of the EV industry in Malaysia is hampered by factors such as high price, slow infrastructure implementation, and technological limitation (Frost and Sullivan, 2019). Even the move by the Government of the United Kingdom to ban new sales of diesel vehicles by 2040 to achieve a sustainable, zero-carbon road transport system is considered too late by some (Shammut et al., 2019).
EVs offer zero CO2 tailpipe emissions and the highest energy efficiency compared to a fuel-based car that produced 152 g km -1 , a saving of 1.7 million tonnes of CO2 (GreenTech, 2015). Among the positive impacts of electric vehicles (EV) are the decline in human toxicity exposure to ozone, and reduction in particulate matter formation which improves air quality as EV performs 8 times better than the Euro 6 diesel vehicles (Hooftman et al., 2016).
It is estimated that a battery electric vehicle (BEV) produces lower NOx emission of 36 mg km -1 (based on 2016 US electric grid) compared to Euro 6 petrol of 60 mg km -1 . Green vehicles will emit zero particulates and CO compared to the 0.3 mg km -1 emission of particulates and 500 mg km -1 of CO from the Euro 6 petrol (Winkler et al., 2018). The emission reduction potential from the transportation sector would be beneficial to Malaysia environmentally when there is mass usage of EV as the air quality will be improved from zero emission of CO and particulate matter, and NOx emission that will be halved.
Kuala Lumpur City Hall (KLCH) is a member of the C40 Cities Climate Leadership. Indeed, the issue of climate change has significantly encouraged the development of more intensive, practical, and integrated acts, policies, and strategies by policymakers and stakeholders in Malaysia. The Kuala Lumpur Low Carbon Society Blueprint 2030 was developed as its commitment to reduce emissions by 70% by 2022 against 2015 levels (Ho et al., 2018). This amounts to a decrease in cumulative emissions of 134,345 tCO2e and a financial saving in energy cost of RM76.1 million over this period of time. Some of the national policies in place include the national target of 40% emissions intensity reduction, Renewable Energy Act, National Green Technology Policy, National Energy Efficiency Plan, and National Policy on Climate Change. It has also committed to a target of 45% carbon intensity reduction by 2030 (relative to 2005 levels) (Kuala Lumpur City Hall, 2017).
In addition to the policies, the implementation of emission reduction focusing on the petrol quality of Euro in Malaysia would be impactful in reducing the amount of air pollutants emitted to the surrounding environment with the implementation of the two types of octane rating fuel for petrol in Malaysia, namely RON95 and RON97. The Euro 4M RON97 commenced in September 2015, as well as the Euro 5 diesel since November 2014. Following the Malaysian government's directive for the implementation of Euro 4M by 1 January 2020, petrol operators such as Shell, Caltex, Petron and Petronas have introduced the new fuel standard of RON95 petrol at their stations. The price of RON95 had increased steadily since it replaced the lower octane RON92 in 2008 due to the gradual reduction in fuel subsidies by the government (The Central Bank of Malaysia, 2011;Omar Kamil, 2015;Shaari et al., 2018;Yunus et al., 2019).
The RON95 petrol produced lower NOx emissions by 7.7% compared to RON97 but produced higher emissions of CO (36.9%) and HC (20.3%) (Salleh et al., 2018). The CO emission from RON97 is also reduced from 4% to 3%, while the reduction from RON95 petrol is from 3% to 2.8% based on the fuel characteristics such as density, octane number and lower heating value (Salleh et al., 2018). Engine speed also reduces the CO emissions from the RON95 petrol by 10% lower than the RON97 petrol.
The sulphur limit for petrol and diesel in Malaysia was still high at 500 ppm in 2007, which coincides with the Euro 2 Standard (Atiqah et al., 2018). Ramalingam and Fuad (2014) found that 60% of diesel samples had sulphur levels above 1000 ppm in 2006, followed by 67% in 2007 and 26% in 2009. However, the concentration of sulphur in all diesel samples in 2011, 2012, 2013 and 2014 were lower than 500 ppm and this value was eight times higher than Euro 4 Standards in Peninsular Malaysia (Ramalingam and Fuad, 2014). Atiqah et al. (2018) also summarized that Diesel Euro 2 (EDE2) significantly improved the engine fuel consumption by 7.39% and for exhaust emissions, EDE2 produced slightly higher NOx and CO in Malaysia. In addition, the U.S. EPA informed that approximately 2% of sulphur from diesel fuel also produces PM emission (Stanislaus et al., 2010).
Malaysia introduced the Euro 2M fuel Standard in 2009, whereby the fuel properties are controlled by the Environmental Quality (Control of Petrol and Diesel Properties) Regulations 2007 (Environmental Quality Act 1974Act , 1974. Since then, all oil companies in Malaysia were required to upgrade their fuel quality to comply with the Euro 2 Standard. Formerly, the sulphur limit was 3,000 ppm for diesel and 1,500 ppm for gasoline (Asian Development Bank 2006). Hence, the Malaysian government recommends lower sulphur to ensure that vehicles use fuels that comply with the Euro 2 Standard. On the other hand, growth in vehicle numbers and modern emission reduction technology demand an adequate supply of low sulphur fuel at levels of 50 ppm and 10 ppm. However, Malaysia moved towards Euro 4 Standard implementations as the next step forward in fuel quality improvement. The Euro 4 Standard restricts sulphur content to a maximum of 50 ppm in fuels (Ramalingam and Fuad, 2014).
The diesel Euro 5M was introduced to the Malaysian market by some oil and gas companies in 2016 (Atiqah et al., 2018). Diesel Euro 5M is a cleaner fuel due to its lower content of sulphur compared with diesel Euro 2M (Stanislaus et al., 2015). The benzene level in the Malaysian Euro 4M is specified at 3.5% by volume, in contrast to the Euro 4 specification for a benzene content of 1% maximum by volume (Asian Clean Fuel Association, 2012). The sulphur content for Euro 4M was set at 50 ppm, similar to Euro 4. The NO x emissions for Euro 4M is capped at 0.15 g km -1 for petrol passenger cars, in comparison to the equivalent figures for Euro 4 at 0.08 g kg -1 or the more stringent Euro 5, with NOx emission capped at 0.06 g km -1 (Asian Clean Fuel Association, 2012).

Uncertainty
Among the uncertainties that arise from this study is that only the new motor vehicles registered in the Kuala Lumpur metropolitan area are considered, which is a small scope on the air quality study of pollutant emissions from motor vehicles for a short period from 2010 to 2014. Notwithstanding, this study does not focus on the older motor vehicles, where age is identified as a major contributor to pollution emissions (Caserini et al., 2013), rather, this study examines the fuel consumption in the process of vehicle movement. Zachariadis et al. (2001) assumed that both the specific mileage, for example, kilometre per vehicle, and the emission factors are independent of vehicle age and therefore independent of time. Experimental emissions data from in-use cars indicated a clear deterioration in the emission behaviour as cars became older, mainly because of the ageing of their catalytic converters and degradation of their emission control systems (Lawson, 1993;Samaras et al., 1998;Ntziachristos and Samaras, 2000). Therefore, age and technological changes determine the internal dynamics of the motor vehicle population and influence the environmental impact of road transport in various ways. Uncertainty also arises from the average vehicle mileage travelled from the mileage variation, which is estimated up to 3% for NOx and approximately 12% for CO as well as the emission factors that also contribute to the uncertainty in calculating the emission of pollutants (Baidya and Borken-Kleefeld, 2009).

CONCLUSION
Urban traffic pollution has resulted from various factors such as urbanisation, population, and the economy of the country. The PM10 emissions from private cars contribute to air pollution with 214,427 kg released in 2014. The highest PM10 emission in Kuala Lumpur was contributed by private cars and motorcycles that resulted from traffic congestion, differences of fuel characteristic in vehicle movement processes, and morphology aspects of the urban background. The growth of EV industry in Malaysia should be encouraged by reducing the exorbitant price of cars, improving the charging infrastructure, and through other strategies implemented by other nations, such as tax incentives on green technological vehicles, which could be one of the ways forward for government agencies to control the negative impact of urban traffic pollution, especially towards human health and urban community.