Abstract

The study investigated the emission of Hydrocarbons (HC), Oxides of Nitrogen (NOx), Carbon monoxide (CO) and Carbon dioxide (CO₂) in vehicles. The study adopted a multiple research design approach to select five cities, garages and vehicles for the study. Whilst the cities were purposefully selected, the garages or fitting shops were selected by first identifying a garage owner who then introduces the researcher to another garage. This approach continued until the 200 targeted vehicles were reached. Two hundred vehicles used for the study were randomly selected as owners of vehicles visited the fitting shops for regular maintenance of their vehicles. The data was analyzed using analysis of variance (ANOVA) to compare the emission of various gasses. The study revealed that diesel vehicles emissions at 34.1 km/hr were considerably reduced when compared with EURO-6. At this speed CO emission was 0.01 g/km and lower than the standard level of 0.50 g/km. Oxides of Nitrogen (NOx) emissions of 2.3g/km was higher than the EURO-6 standard of 0.08g/km. Hydrogen Carbons (HC) emission of 0.65g/km was higher than EURO-6 standard of 0.17g/km. It is recommended that advanced technologies with no or little gaseous emissions must be adopted by vehicular manufacturing nations to curb or reduce the emission of harmful gases that leads to global warming.

1. Introduction

Transport is a vital part of modern life as it serves as a means by which societies interact. Efficient transportation provides economic and social benefits that result in multiplier effects such as better accessibility to markets, employment and industrial growth among others. Owing to this flexibility, road transport has played a pivotal role as a major transport mode, and vehicles are objects of desire and pride in many societies ¹.

Despite the benefits of transport especially road transport, the negative impacts on the environment and human health to a large extent offset the benefits ². Research scientists show that, from year to year the prevalence of carbonic gas in the atmosphere increases. This leads to the so-called “greenhouse effect”, i.e. an increase in the average annual temperature on the planet by an average of 0.8-3.0%, which, in turn, will lead to significant climate changes. Except direct negative impact on health of the person, emissions of the motor transport have greenhouse and ozone-depleting effect on the atmosphere of the earth ³.

Acidic oxides in the ground layer of air are strong oxidants, adversely affecting the respiratory system of living organisms, plant growth and causing acid rain. Thus, the annual damage to US agriculture from increased concentrations of oxides is estimated at $ 1.9-4.3 billion. Approximately 30% of the acid rains in UK are due to nitric acid presence in them. Therefore, in the majority of developed countries, the emissions of the substances are limited and strictly monitored for their reduction ⁴.

Reactions involving hydrocarbon constituents also play an important role in the formation of NO (“fast” NOx ). CH radicals existing in the flame front can react with atmospheric nitrogen to form cyanic acid, which in turn reacts according to the scheme. Unlike “thermal”, “fast” NOx can form at lower temperatures (~700°C) ⁴. Annually in the atmospheric air about 180 million tons of nitrogen oxides are emitted ⁴. The source of NO can be from atmospheric N₂ which is part of the fuel components (“fuel” NOx) ⁵.

The main contribution to the formation of nitrogen oxides is made by high-temperature processes (T> 1,100°C) of air nitrogen oxidation. Among the anthropogenic sources, motor transport contributes most to the pollution of atmospheric air with nitrogen oxides ⁶. Such a high figure is primarily associated with the constant expansion of the world’s automobile fleet, which today has about 1.5 billion units, and by 2030 could reach 2.7 billion units ⁷. This is evidenced by the statistics: for the last 15 years, sales of cars have grown by 40.5% (from 51.55 million in 2000 to 72.41 million in 2015). The exhaust gases of vehicles, depending on the type of engine (two- or four-stroke gasoline or diesel), operating conditions, the speed they develop, etc. on the average contain from 11 to 13 g NOx per 1 liter of fuel ⁸. Thus, the average car with an annual mileage of 16.7 thousand km and a fuel consumption of 10 liters for every 100 km of the path emits about 20 kg of NOx into the atmosphere. Internal combustion engines generate N₂O, NO, NO₂ ^{3, 9, 10}.

Research conducted in recent decades has revealed that outdoor air pollution harms health and the evidence points to air pollution that stems from transport as an important contributor ¹. The main consumer of motor fuels (the most common type of petroleum products) is road transport. The differentiation of pollutants in the atmosphere from the motor transport is a difficult task ⁴. Exhaust gases are the waste substances which are in the engine; they are products of oxidation and incomplete combustion of hydrocarbonic fuel ¹⁰.

The most numerous, massive and dangerous components of gas emissions of cars are hydrocarbons, of which there are more than 200 > 32% are saturated hydrocarbons; ~ 27% - unsaturated hydrocarbons; - up to 4% - aromatic hydrocarbons; ~ 2% - aldehydes ¹¹. With gas emissions of motor vehicles, 37- 85% of lead and its compounds contained in leaded gasoline enter the atmosphere, and their concentration in emissions is 50-1,000 μg/m³. A significant number of these compounds fall into the environment as a result of evaporation of gasoline. The total proportion of lead and carbon monoxide compounds in gas emissions of cars exceeds 75% ^{3, 9, 12, 13}.

Within the EU, the work on the environment in relation to cars is to protect air quality. Different means are used to accomplish this. One way is to use emission performance standards for CO₂. Another is the system of Euro standards establishing emission limits for other harmful pollutants such as nitrogen oxides and particulates. In order to compare negative impacts of pollution in decision making, the IPA has been developed in the EU-funded External projects ¹⁴ and is now used in preparations of regulatory policy proposals at the EU level.

The component of these emitted gases include Seven (7) different gases; Carbon Monoxide (CO), Carbon Dioxide (CO₂), Oxides of Nitrogen (NO_x), Hydrocarbons (HC’s), Particulate Matter (PM), Nitrogen (N) and Oxygen (O₂) which constitute the bio-product of combustion of an engine. Some of these gases can be toxic and also contribute to greenhouse gas (GHG) emissions which eventually lead to global warming ¹⁵. In addition, nitrogen oxides contribute to an increase in the ozone concentration in the surface layer, and also participate in the formation of photochemical smog ⁴. Combining with atmospheric moisture, NOx form weak solutions of nitrous and nitric acids, which leads to the precipitation of so-called “acid rain”. Under the influence of acid rain, soil acidification and depletion of nutrients, acidification of surface water bodies, degradation and complete destruction of forest areas occur. In addition, nitrogen oxides contribute to an increase in the ozone concentration in the surface layer, and also participate in the formation of photochemical smog ⁴.

Despite the fact that modern automotive technologies can significantly reduce nitrogen oxide emissions by improving the engine design and its optimal adjustment, the NOx level still exceed the legal norms ¹⁶. For this reason, an increasingly urgent task is the development of new methods for additional purification. Since the reduction of nitrogen oxides to an environment friendly molecular nitrogen is a thermodynamically advantageous process, cleaning the car’s exhaust gases is essentially a kinetic problem, and therefore the main method of neutralizing NOx is the installation of catalytic systems ^{17, 18}. The choice of catalyst depends directly on the air/fuel ratio, the composition and temperature of the off-gases, and therefore the catalytic purification schemes for cars with petrol and diesel engines differ significantly from each other. The concentration of nitrogen dioxide is higher in daytime and evening and is associated with the most intensive traffic. The concentration of sulfur dioxide increases by the end of the day. In the warm season, the concentration of all impurities is less than in the cold season, with a decrease towards the end of the day ^{3, 9}.

It has been estimated that about one hundred and seventy-thousand (170,000) people die prematurely each year in Africa due to outdoor air pollution ¹⁹. Air pollution emanating from vehicle exhaust gas emissions is a significant risk factor for a number of health conditions including respiratory infections, cardiovascular diseases ²⁰ such as stroke, lung and other forms of cancers and asthmas ¹⁹. Traffic is the most important source of outdoor air pollution in urban areas in Sweden ²¹. In general, the scientific research strongly indicates that traffic emissions do generate a negative impact on human health ²².

Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes. Increased awareness regarding the adverse effects of pollutants from automobile exhaust gases has been the main driving force for implementation of more and more stringent legislation on automobile exhaust emissions in many countries ²³. Emissions legislation is in force in North America (Canada and the United States of America), Europe (European Union, UK, Germany) and Asia (China, Hong Kong, Japan, and India) and in Africa (only South Africa) ¹⁴. It is therefore clear that Ghana has no emission legislation put in place to regulate the thresholds of vehicle emissions in the country or if they exist they are not enforced.

The present trend in Ghana shows an increase in fleet population over the past 20-years with a resultant negative impact on local air quality and increase in greenhouse gas emissions which has global warming potential. Vast majority of these vehicles are over-aged and in most cases are not permitted to be used at their country of origin due to their strict vehicle roadworthy regulations and compliance with the environmental protection standards on pollution as well as their ultimate effects on human health ²⁵. Unfortunately, in Ghana, the officials of the Department of Vehicle and Licensing Authority (DVLA) usually conduct physical examinations on vehicles before issuing a roadworthy certificate to the detriment of a mandatory vehicle emission test to ensure that exhaust gas emissions are within acceptable standards for public health and safety ²⁶. This study therefore is to create the consciousness and public awareness of the dangers of vehicular exhaust emissions in Ghana. It will also serve as a benchmark for future studies in vehicular exhaust emissions by both students and policy makers.

2. Materials and Methods

The study was conducted in Accra, Tema, Takoradi, Tamale and Kumasi selected from the sixteen (16) regions in Ghana because of time and resource constraint. These cities are also the major cities in Ghana.

To gather data from various selected vehicles, there was the need to use specific and precise materials and equipment. Table 1 shows the details of the equipment and materials used in testing the vehicles for emission factors and values needed for the study.

The chassis dynamometer is a significant element in Emissions testing, faults diagnosis and performance profiles of vehicles. The non-availability of chassis dynamometer did not permit certain engine parameters during the emission test. Parameters such as; engine performance and evaluation, vehicle heating and cooling systems, drive train components evaluation, fuel efficiency, transmission components, tyre testing, failure analysis and auxiliary components.

This research was implemented by the use of descriptive statistics comprising quantitative and scientific exploratory analysis. A multi-stage sampling technique was employed in the selection of vehicles, towns and workshops (Fitting shops) locations for the experiment. According to ²⁷, multistage sampling is defined as a sampling method that divides the population into groups (or clusters) for conducting research. In the first instance, a purposive sampling was used to select five cities across the country. These included; Tamale, Kumasi, Accra, Takoradi and Tema. The locations of viable fitting shops were sampled by first identifying a fitting shop owner who then introduces the next fitting shop to the researcher. The process continues until all major fitting shops were covered in the study. After the fitting shops were identified, a simple random sampling technique was used in the second stage to select prospective vehicles, thus vehicles which have been brought to the shop for repair or maintenance work. According to ²⁸, the simple random sampling helps due to the fact that anyone is chosen entirely by chance and each member of the population has an equal chance of being included in the sample.

The sample frame of the study was 416 out of which a sample size of 200 vehicles was selected for the study. The figure was arrived at through the use of the formula proposed by ²⁹ as shown in equation (1). According to them,

(1)

Variables:

The respective variables have been given their explanations below.

From the information above;

The probe of the Exhaust Gas Analyzer was placed in the exhaust system of the engine to collect gases (Figure 1). The major component of the gases measured includes Carbon Monoxide (CO), Oxides of Nitrogen (NOx), Hydrocarbons (HCs), Carbon dioxide (CO₂) and Particulate Matters (PM). Different analytical techniques were adopted to measure the exhaust emission concentrations. The calibration and the calculation of emission results in terms of engine speed, temperature and load conditions, measurement of exhaust gas concentration and other engine operating parameters were considered. An experimental specimen form was designed and used to collate the required information on parameters which were measured during the experiment in the workshop/ Laboratory for the analysis.

Data analysis is critical for bringing out the meaning of all the experiments and data gathered from the vehicles. This research focuses on the use of the Analysis of variance (ANOVA) to explain the emissions and the quantitative data from the investigation. Two main soft-wares were used for the study; the first one was performed on primary data using GenStat PC software (version 17) and the second software was done using the Statistical Package for Social Scientists (SPSS) version 24. The Pearson’s correlation was adopted in testing the confidence level, relationship between the various cars and the emission level or status they produce.

3. Results and Discussions

The data were collected on 200 vehicles across the five sampled cities. From the data petrol engine (spark ignition) was the majority and represents 133 (66.5%) of the sample cars, while, those cars with diesel engine (compression ignition) represents 67 (33.5%) of the sampled cars. In relation to car ownership type, the data gathered from the respondents (owners) and as well as by observation showed that majority 121 (60.5%) were privately owned cars (non – commercial) while 79 (39.5%) of them were commercial vehicles or passenger cars.

Within the context of year of vehicle manufacture, 101 (50.5%) of the sampled cars ranged between 2000 and 2006; this was followed by 50 (25.0%) vehicles manufactured below the year 2000 while vehicles manufactured between 2007 and 2013 numbered 41 (20.5%). The least of the cars were cars manufactured within the period of 2014 – 2019 representing 8 (4.0%) of the sample respondents of cars selected for the study (Table 2).

Table 3 shows a cross-tabulation between car engine type and ownership type. From the cross-tabulation between engine type and car ownership type shown in Table 2, it can be seen that a total of 133 (66.6%) were those having petrol engine cars. Of this, 101 (75.9%) were private cars and 32 (24.1%) being passenger cars. Also, 67 (33.5%) of the cars were those having diesel engine; of which 47 (70.1%) were for private use and 20 (29.9%) being passenger (commercial) cars.

Table 4 presents a cross tabulation between car age and engine type. It was shown that majority (82, 81.2%) of the 101 cars were those which were petrol engine type, 19 (18.8%) of the 101 cars were diesel engine type engines and were manufactured within the period 2000 – 2006; this was followed by 42 (84.0%) of the 50 cars that were of diesel engine type and manufactured within a period below the year 2000. Thus, 35 (85.4%) of the 41 sampled cars were manufactured within year 2007 – 2013 being petrol engine type. The least number of the cars (6, 14.6%) of the 41 cars were diesel car engine type and manufactured between the years 2007 – 2013, while, none of the cars manufactured between the years 2014 – 2019 were diesel engine type.

In this section, the various test load condition of the sampled vehicles was established. Thus, the research study recorded data on vehicle pollutants at 4 stages of load conditions. An engine load basically determines the capacity of the engine to produce power. Consequently, all sampled vehicles for the experiments have engines designed for particular load called rated load or maximum load at particular speed. Whenever the load on engine increases, the engine speed decreases. The engine load was measured at 10% interval up to 80% of the load condition depending on the car. While measuring the revolution per minute (rpm) on the dashboard of the car at various stages of rpm; 1200 rpm, 1600 rpm, 2000 rpm and 3600 rpm. Data records gathered were analyzed taking into strict consideration the respective vehicle pollutants at various different engine load conditions.

In order to make a comparison analysis with EURO-6 emission standards, the vehicles were driven at various drive cycles of average speed: 4.7 km /h and average speed: 34.1 km/h, this was done in order to produce a reliable and relevant data on emissions for comparison with EURO-6 compliance for both diesel and petrol or gasoline fuel engines. The data showed that while cars before the year 2000 do not have strong emission compliant systems or technology, they were producing relatively higher emission compared to that of cars made later than 2006 with EURO-5 and 6- compliance ³⁰.

In relation to the diesel engine type, the data gathered and illustrated in Figure 2 beneath indicates that the Oxides of Nitrogen (NOx) emission from diesel vehicles were higher at 4.7 km/hr with a data of 1.4 g/km, while, that of the Hydrogen Carbons (HC) was 0.58 g/km. In this regard none of the Carbon Monoxide (CO) was recorded in the data collected.

Comparing the data with standards set by Euro-6 for diesel engines: carbon monoxide - 1.0g/km, total hydrocarbon - 0.10 g/km and nitrogen oxides: 0.06 g/km. The data showed that diesel vehicle emission on NO was higher than EURO-6 standards, thus 1.4 g/km > 0.06 g/km. This means the vehicles used for the tests are producing much more NOx emissions by a factor of 10 at 4 km/hr, while in relation to CO there were no emissions in that regard. Concerning HC, the vehicles produced 0.58 g/km compared to EURO-6 standards of 0.10 g/km. The study undertaken by ³¹ concludes that the difference between gasoline and diesel vehicles was small and that it was more important, from an environmental point of view, to choose fuel efficient cars. ³² on the other hand finds that diesel cars have higher emissions of NO x and particulates (unless they have a diesel particle filter). That diesel cars are more harmful is also found in recent research by ³³ and ³⁴ based on results from external cost calculations in Belgium. According to ³⁵, the external cost of diesel cars are in general higher than for gasoline cars, irrespective of Euro standard.

Also, as illustrated in the Figure 2 beneath, comparing the diesel vehicle emissions at 34.1 km/hr, the emission reduced considerable as has been explained in earlier segments above. However, at this speed there was a CO emission of 0.01 g/km, this data showed that compared with EURO-6, the vehicles emission was in comparison lower than the standard level of 0.50 g/km. In relation to Oxides of Nitrogen (NOx) emissions, the data recorded from the vehicle tested showed that NOx emission was averagely 2.3g/km which showed that this was higher than the EURO-6 standard of NO (0.08g/km). Also, in relation to Hydrogen Carbons (HC) emission from the test, the average value was 0.65g/km, which also proved to be higher than EURO-6 standard of 0.17g/km. The data agreed with the assertion by ²⁷ concerning the vehicles within the system and how they fall below the standards of EURO-6 for diesel vehicle emissions and pollutant substances.

This issue has been studied by IRAC (International Agency for Research on Cancer) and their conclusion is that diesel emissions are carcinogenic while gasoline emissions might be ³⁵.

In relation to petrol or gasoline fuel engine types, as illustrated in Figure 2 the various drive cycles tested showed that the higher the average speed the higher the emission levels. In context of the carbon monoxide (CO) tested from the vehicles on 4.7 km/hr average speed, the average value from the test showed 0.12 g/km of CO emissions from the vehicles tested which when compared with EURO-6 CO emissions of 1.0 g/km is quite lower than the standards. This means that petrol vehicles driven with 4.7 km/hr have lower emission of CO. while, there was no HC emission recorded, in context to Oxides of Nitrogen (NOx) the value was 0.021 g/km in comparison to EURO-6 standard of NO = 0.06 g/km. The data showed that the petrol vehicles met the standard and even outperform within the 4.7 km/hr driven.

In relation to drive test within 34.1 km/hr, the data illustrated from Figure 3 showed a higher level of emission from the test results. While, there was no HC detected from the test drive in relation to EURO-6 emissions, the Carbon Monoxide (CO) data produced 0.25 g/km averagely for every km. In comparison with EURO-6 standards of 1.0 g/km this proves petrol engine performance have been held appropriately within the standards. In relation to Oxides of Nitrogen (NOx), while the emission was quite higher than that of the 4.7 km/hr driven tests, the emission was 0.04 g/km which was close to the EURO-6 emission standard of NO = 0.06 g/km. The data clearly showed that there was much performance within the system of petrol vehicles. The data agreed with ²⁷ that most petrol fuel type cars with current year of 2004 and above were fine tuned to meet EURO-6 standards and performed much better.

In this section descriptive data were gathered concerning factors contributing to an excessive vehicle exhaust emission among the various cars test driven and given ratings based on their pollutant factors.

As observed from Figure 4 above, the majority (43.0%) of the factors were attributed to the vehicle age. Thus, the vehicle manufacturing age contributes excessively to the emission into the atmosphere. Thus, older vehicles have higher emission rates. Due to some cars which were manufactured prior to EURO-5 and EURO-6 emission standards, the technology used in mitigating emission are weakened and does not contribute to proper emission levels. This was followed by engine capacity representing 21.0% of the factors contributing to excessive exhaust emissions among cars. Thus, the bigger the engine size the more emission it produces, this is because the horsepower produced by the cars needs extra fuel to maintain the engine performance thereby producing more emissions.

Seventeen percent (17.0%) of the factors were attributed to mileage or the length at which the car has been driven. This was crucial since, the emission sensors needed to be replaced at some high number of mileages driven. A vehicle driven for so long tends to have poor emission detection systems thereby increasing the level of emission from the vehicle. Also, 15.0% of the sample indicated that the type of fuel contributes to exhaust emissions. Furthermore, untreated or quality of fuel contributes excessively to fuel emissions. The least of the factors were grouped into others representing (4.0%). Theses others factors includes; vehicles without emission controls technologies, inadequate maintenances schedules and bad road conditions.

The relationship between different types of emissions depends on the engine and exhaust treatment technologies ³⁶. First of all, the share of diesel cars has until recently been comparatively small ³⁷, but is now growing, increasing the emissions of NOx and exhaust PM even in areas where total traffic is steady. The data concerning factors contributing to vehicle emissions were supported by ³⁸ that poor emission technology exists among other factors in old age cars. In furtherance, they explained that cars older than 2000 have about 23.0 – 25.0% chance of increasing emission pollution compared to cars newer than 2006. Also, ³⁹ indicated that cars manufactured before the year 2000 have been noticed to have lower level of emission technologies compared to those manufactured after the year 2010 or later due to upgraded technologies to control vehicle emissions.

4. Emission Legislation and Testing

The need to protect the environment and human health in most countries have instigated legislation and testing strategies to help ensure that the level of pollutant emissions are controlled. This has proved to be critical since many of the actions of manufacturers was to ensure that cars manufactured are regulated in terms of the pollutant formation and other intricate details necessary for lower exhausts and pollution emissions in the short and long term. Emission legislations have proved to be critical in ensuring every car owner or manufacturer works within the standards on emission. Emission legislation sets the standards for operation and what rules and regulations should be followed in the case of emanating from the legislative instruments of various manufacturing and emissions strategies. As described by ⁴⁰, there is an ongoing discussion on how to improve test procedures and the test cycle, and a project called WLTP (world harmonized light-duty vehicle test procedure) is underway.

5. Conclusions and Recommendations

In conclusion, the study revealed that diesel vehicles reduced emissions when compared with EURO-6. The test cycle shows that, petrol vehicles performed better within the drive tests compared to diesel vehicles. This indicated that most petrol fuel type cars were fine tuned to meet the EURO-6 standards and performed much better than diesel engine vehicles. The study showed that the factors impacting on the level of emissions for vehicles were attributed to the vehicle age. Cars manufactured prior to EURO-5 and EURO-6 emission standards have weakened emission technologies and do not contribute to proper emission levels. Also the bigger the engine sizes the more emission it produces because the horsepower produced by the car needs extra fuel to maintain the engine performance thereby producing more emission. The study recommends that, better emission technologies with little or no emissions must be adopted by all nations. This will help reduce the greenhouse gases that are produced by automobiles.

References