SUMMARY Riyadh is an interesting city in which to study the effects of various gas emissions into the air. Because it is the capital of Saudi Arabia, it is the most populated city in the country, as well as being the most dense, which leads to various problems such as congestion from traffic, urban traffic noise, and poor air quality from pollution. While various sources have been held responsible for these potentially unsustainable conditions, nearly 30% has originated from transport (both passenger and commercial vehicles). One way I attempted to add to previous studies done in this area was to quantify the concentration of carbon dioxide that was dispersed from a point source close to the ground over a specific time interval. In my case, I chose the last 51 years in Riyadh. After gathering the necessary data from the World Bank, I attempted to create a Gaussian Dispersion Model in order to measure the dispersion downwind from the point source (in this case, the car), which gave me values between 0 and 7 μg/m3 (I have included a graph in the Results section). While this doesn’t appear to be a very large number, it is still important to take the number of cars that are dispersing this pollutant on a daily basis, as well as how that accumulates over long periods of time. I then related this to the ongoing construction of the Riyadh Metro, which is proposed to help mitigate some of the socially and environmentally unsustainable practices in the city.   1. INTRODUCTION While most of the continents are experiencing some sort of population growth, regardless of whether or not it involves urbanization, one continent that is going through it more than others is Asia. It is common knowledge that China has one of the largest populations in the world at over 1 billion people, with India not too far behind. However, they are not the only ones currently experiencing growth in both population and urbanization, but another country is as well: Saudi Arabia. The Kingdom of Saudi Arabia is located in the Middle East, with some of its prominent neighbors consisting of Yemen, Oman, Iraq, Iran, Egypt, the United Arab Emirates, and Qatar to name a few. This part of the continent is one of the most interesting as far as studying urbanization and sustainability goes, since it is this area that is currently considered a pioneer in attempting to devise new ways to utilize methods that will cut down on carbon emissions and rely more heavily on renewable energy sources and solar power. One example of this is an ongoing project in Abu Dhabi, the United Arab Emirates, that is currently building a section of the city, Masdar City, that is aiming to be a carbon-neutral city. Without carbon, all vehicles will be run on solar power, and the need for air conditioning would be cut down as well, with windows being built to the north to allow for cooling in the summer. That is just one example of keeping a city in the Middle East sustainable. For Saudi Arabia’s capital, Riyadh, it is a different story. The focus on this city will be mostly on transport and the current problems that come with it, as well as what can be done in order to mitigate them and create a sustainable environment for the Saudis. This is especially important because of the constantly increasing population, which will need to be monitored in order to make sure that any alternative methods of transport or otherwise will be able to sustain everybody. Figure 1. A graph showing the increase in Saudi Arabia’s population over the last 50 years. The data comes from the World Bank.



  1.1 Transport and Environmental Issues in Saudi Arabia In addition to being the capital city of Saudi Arabia, Riyadh is also the largest one in the country at 600mi2. According to the 2004 census, the population in Riyadh was 4.087 million, which has only increased over the last decade, as shown by the above graph of population vs. time. This also means that more people will be using the roads for transportation, and therefore, more vehicles. The World Bank and OICA are just two places that have shown evidence that as the years go on, there has been an increase in the number of registered vehicles in Saudi Arabia, as seen in the chart below:

Figure 2. Number of vehicles in Saudi Arabia over the last decade. After seeing a value of almost 6,000 vehicles at the end of 2013, it can only be assumed that this number has and will increase even further due to urbanization and the need to get to several areas around and outside the city, such as airports and other places in the country. Several studies done in the past have shown that this has had several detrimental effects on the environment in Riyadh, however, one of them being diminished air quality. Air pollutants are constantly monitored in Riyadh, the main reason being for health. Previous air quality assessments conducted by the Presidency of Meteorology and Environment (PME) and the King Abdulaziz City for Science and Technology (KACST) have shown a correlation between pollutants in the form of falling dust and toxic chemicals, and several health problems such as asthma, lung injury, bronchial constriction, and other infections. These are all believed to also be caused by metallic pollution, with the culprit being the cars that are constantly on the road. Further calculations of the air quality index in Riyadh back in 2004 also revealed that the number one pollutant in the capital city was PM10 with a concentration of around 1000 μg/m3, which exceeds the concentrations that are normally considered to be hazardous. SO2 and H2S were also found to be top pollutants in Riyadh at this time while ironically, CO2, CO, and O3 were shown to be in the good range. However, those three pollutants have shown an upward trend in the last decade, again with the increasing number of registered cars on the road. As previously mentioned, falling dust is another problem in Riyadh. This is already added to the fact that dust storms frequently blow through not only this area, but the entire Arabian Peninsula. About 392 tons/km*yr of dust fall on the capital city, which run the risk of raining down particles of lead, aluminum, copper, and iron, which are also hazardous to human health. High traces of CaCO3 were also found, and the following table shows some of the most common trace elements found in dust over Riyadh. As shown by the table, zinc and manganese were the ones with the highest concentrations.

Table 1. Total concentration (μg/g) of trace elements in the fallout dust samples of Riyadh City

While not as major of an issue as some of the ones already described, urban traffic noise is also a growing problem in Riyadh, as this more concerns social sustainability than environmental sustainability. In a study conducted on the effects of too much noise, many people reported feeling nervous, as well as suffering from headaches and hearing loss, which would make sense considering how densely populated Riyadh is. Some of this may come from the many cars that are on the road every day, so finding a way to minimize the amount of traffic noise would help to make the city a more sustainable place to live in.

1.2 Comparing to Other Regions The entire Arabian Peninsula and Persian Gulf Region is a large area of interest when it comes to studying carbon emissions and other phenomenon associated with the climate of the area, such as the dust storms that were previously discussed. The Arab world is one of the places with the most carbon emissions in a year, as shown by the graph below. Figure 3. Carbon dioxide emissions (in kt) in several Arab countries. While all of the above countries have experienced an upward trend in CO2 emissions over the last fifty years, Saudi Arabia and Iran have shown the most dramatic increase. Adding to this is the fact that more data collected by the World Bank shows that in Saudi Arabia, anywhere between 20 to 40 percent of these emissions goes towards fuel combustion, which includes operating motor vehicles along with other uses. This is an awfully high number when compared to a country like the United Arab Emirates, which as previously mentioned is currently aiming for carbon-neutral sections of Abu Dhabi, like Masdar City. This also coincides with the increasing problem of ozone pollution over not only Saudi Arabia, but the entire Arabian Peninsula and Persian Gulf Region. A study conducted in 2006 showed that this was one of the areas to experience the highest concentrations of O3, with the summer amounts having the highest values.









Figure 4. Model calculated monthly mean surface O3 in excess of 40 ppbv in the period January to December 2006. The arrows indicate the mean surface winds. As an earlier graph showed, the number of cars on the road in Saudi Arabia has been steadily increasing. What can be said about the number of vehicles in other Arab countries? That will be covered when alternative methods of transport are introduced. Despite these climbing numbers, however, the Arab World overall is still not the world’s largest emitter of carbon dioxide, with that title going to places like North America (mainly the United States), China, and the European Union. This is due to the fact that these areas are much more urbanized and industrialized than the Arab World, though that could change in the next several decades as the emission numbers continue in their upward trend.

Figure 5. CO2 Emissions in the Arab World, the European Union, and North America. 1.3 Energy Usage in Saudi Arabia The statistics of transport and environmental issues in Riyadh have been discussed. Now, it is time to look at the amount of energy being used. As with many of the other variables that have been studied so far, there has been an overall upward trend of energy consumption in Saudi Arabia as a whole compared to other Arab countries which haven’t seen as dramatic of an increase, some of them even showing a decrease (e.g. the United Arab Emirates). The decrease has been shown to be related to the growing use of alternative and renewable energy sources, so the opposite can be said for an increase, in which less environmentally friendly methods are used and end up contributing to the increase in carbon dioxide emissions. First, it is important to look at the actual amount of energy being consumed per capita for the entire country. Over the forty-one year time frame that the data was collected (1971-2012), annual values ranged between 300 and 8500 kWh per capita, the average amount coming out to 4074 kWh per capita, which equals 15 kW per capita. That is already a very high amount compared to some of the other countries other than the United Arab Emirates (though as previously mentioned, this is still smaller than the United States, China, and Europe), as shown in the following graph:






Figure 6. Average electric power consumption in several Arab countries from 1971-2012

This high value is part of the reason why something needs to be done in order to make transportation more sustainable in Riyadh in particular. For example, consider the power consumption in just one year, like 2012. The amount for that year alone was 8404 kWh. Dividing that number by 12 reveals that at least 700 kWh were used per month. Now taking one 30-day month into consideration, a value of around 23 kWh would be the total for just one day. This is simply looking at the general picture, however. It is important to see where this electric power is going as well. Previous data for this same time period has shown a slight decrease in the percentage that originates from oil, gas, and coal sources, but not by that much. For example, in the 1970s and 1980s, 100% originated from the three previously listed sources, when alternative sources of power were not as readily available. By the time the 1990s came around, these percentages had decreased to between 60 and 70%, only to increase back to anywhere close to 80 and 90% by the new millennium. This can be attributed to the increase in motor vehicles, including passenger cars, being produced and sent out on the roads, along with burning fossil fuels. This can also be backed up by the fact that between 20-30% of carbon emissions come from transport, which is also an alarmingly high number. Because Riyadh is such a large city, this poses a major problem on the overall health and wellbeing of everyone who lives there and why alternative methods are currently being planned out, such as one that is hoping to make a significant impact on living conditions in this part of the country. One of the main ongoing projects that is hoping to accomplish this is the Riyadh Metro and Light Rail, which will be discussed later.   2. METHODS While the previous studies discussed have covered quantifying emissions and falling dust sediments, I have attempted to quantify the concentration of carbon dioxide in a different way. As I investigated previous case studies, I began to wonder how much carbon dioxide was possibly being dispersed from individual cars, which could potentially explain why there seems to be a looming issue with pollution and poor air quality in Riyadh. In order to do this, there were several assumptions that I had to make, as well as finding the correct equation that would satisfy these assumptions and help give me the answer I was looking for. The solution eventually came in the form of the Gaussian Plume Dispersion Model equation.

2.1 Gaussian Plume Dispersion Model The Gaussian Plume Dispersion Model was extremely useful in my analysis, which I decided to do for an average summer day in Riyadh since most of the other studies were conducted during this same time period. As I began to utilize it, I realized that I had enough data to be able to make assumptions and fit them into the variables that are used to calculate the concentrations that are dispersed.



Figure 7. Gaussian Plume Dispersion Model Equation

Not only was the emissions data from the World Bank useful, but there was also available data from Weather Underground, where I was able to retrieve historical data for Riyadh, which was taken from the weather station near King Khalid International Airport. This was important because part of the Gaussian Dispersion equation requires the horizontal wind speed (in m/s). Through the data from Weather Underground, I was able to calculate an average summer wind speed of 6.68 m/s. As previously mentioned, the other main component of the data came from the World Bank, where I found the carbon dioxide emissions (in kilotons) over the last 51 years and averaged the values together. After I did that, I then divided that number by 51 in order to get the concentration in kilotons/year, which I converted to grams/year in order to get a value of 3.85x1012 grams/year. Further conversions are necessary in order to bring this number to grams/second, which reveals an emission rate of 1.22x105 grams/second. Now come a few assumptions. I own a car, so I decided to assume that all cars driving down a highway in Riyadh were the same height, in which mine turned out to be around 4.85 ft (around 1.48 m), so that was the stack height I decided to use as opposed to a building or a regular stack. This is also partly due to the assumption that the emissions are taking place at ground level. I also assumed that there was neutral to slight instability due to the time of year and the average wind speed calculated earlier, and that this was occurring during daytime hours as well. The instability comes from what is known as the Pasquill-Gifford Stability Classes and Expressions for σy and σz, the latter two terms being dispersion coefficients in the y and z directions. The Pasquill-Gifford Stability Classes are divided into classes A through F, with A being Extremely Unstable and F being Extremely Stable. Neutral to slight instability is considered Class C, and this also depends on how strong the amount of solar radiation is over a particular area. On a summer day in Riyadh, the amount of sunlight would be very strong due to its arid climate, so these assumptions definitely fit. Below is a consolidated table of all the variables that will be used in the Gaussian Plume Dispersion Model Equation, where I will proceed to find concentrations at 500, 1,000, 5,000, and 10,000 meters downwind from the initial source (the car): Variables Values (with units) Q 1.22x105 (g/s) Us 6.68 (m/s) σy ~26,000-319,000 m σz ~17,000-268,000 m h 1.48 (m) Table 2. Variables input into the Gaussian Plume Dispersion Equation

2.2 Results After creating an amateur Gaussian Plume Dispersion Model, I found that the highest concentrations (in μg/m3), while in a small range, were still the highest at the point source (starting at 500m), which would be considered to be where the car is first emitting carbon dioxide into the air from the exhaust pipe. Below is a graph showing what the dispersion will look like as it continues downwind away from the car:




Figure 8. Gaussian Plume Model Results While the numbers may not look big, there is still the matter of thousands of cars at the same height driving at the same time of day, which would all release carbon dioxide around the same time. This is not a perfect model, however, as it disregards other types of vehicles such as commercial vehicles and other passenger vehicles that might be more akin to SUVs, and therefore, at a slightly higher height. This is also only considering summer time, as carbon dioxide emissions greatly vary throughout the seasons. However, it has been shown through previous studies that concentrations are lower in the winter time, so this could also play a role in how gases are dispersed from passenger cars and other types of vehicles as well.  3. PROPOSED SOLUTION AND CONCLUSION 3.1 The Riyadh Metro Project








Figure 9. Projected map of the Riyadh Metro/Light Rail System

As mentioned in the previous section, the Riyadh Metro/Light Rail System is an ongoing infrastructure project funded by a contract awarded to the Bechtel Consortium in 2014. This consists of several companies and contractors such as Almabani General Contractors, Consolidated Contractors Company, and Siemens, and the original contract awarded to the project was $10 billion. The budget has since increased to $22 billion, which was eventually set as the starting price for construction in 2014. This includes designing the stations, actually building them, digging out tunnels for underground tracks, setting up the signals, constructing the cars, and electrifying the tracks. The map on the previous page shows what the potential metro will look like once all construction is completed by 2018-2019. There will be a total of six lines running through the major parts of Riyadh and one even providing access to the King Khalid International Airport (the yellow line, Line 6). In response to some of the previously mentioned environmental issues in the capital city, this project boasts the goal of long-term sustainability. Some examples are utilizing trains that operate automatically and on entirely renewable sources. Riyadh is hoping that the new metro system will eventually meet LEED certification, as well as implementing heating, ventilating, and air conditioning via HVAC. By converting to renewable energy sources, this means that there would be less of a reliance on oil, gas, and coal, which could also eventually cut down on the number of cars being used in Riyadh. This could also lead to lower percentages of carbon dioxide emissions that come from transport, possibly decreasing from the value that it is at now (20-30%) to anywhere between 0-5%. The best bet would be to have the metro help to make Riyadh begin to follow the path to becoming a carbon-neutral city. Another advantage to having a metro system like this one is that it could reduce congestion on the roads, as well as the urban traffic noise that had been bothering people, which would improve the health and well-being of Riyadh’s citizens. This would also greatly improve the air quality, reducing the amount of pollution from PM10, SO2, CO2, O3, and H2S. While the Riyadh metro definitely has its advantages, there are a few disadvantages to constructing it as well. The first one is just how expensive it is. Even with the $10 billion contract it was awarded, it is still very expensive at the $22 billion that was mentioned on the previous page, which could prove to not be very cost-effective unless the various contractors and companies working on this project could tunnel through the cost barrier that is sure to form. There is also the problem of the fact that this is the first time a project like this is being constructed in Riyadh, which is considered a highly populated and dense city. Because of this, there is a lot of room for error and potential for things to go wrong, in which the companies have to make sure the workers are in safe conditions. This is due to digging underground in order to build the necessary tunnels to lay the tracks down, so extra precautions must be taken. This could also affect the stability of the buildings above ground, so this must also be monitored carefully during this whole process. One more disadvantage that could come with a system like this one is the ever growing population of Riyadh, which is expected to increase to at least 8 million by 2030. One question that is often raised when it comes to something like this is whether or not this new metro will be able to sustain this many people by that time.  3.2 Conclusion Looking at everything from the World Bank data, to the number of registered cars, the various environmental issues, the results from the Gaussian Plume Dispersion Model analysis, and the urban traffic noise study, it can be concluded that the Riyadh Metro, while not perfect, is a good start in order to make the city more environmentally and socially sustainable. It is only a matter of time before the project is completed in a few years, so that will be the true test to see if it is truly helping to cut down on carbon dioxide emissions. If this is a success, then perhaps Saudi Arabia as a whole can start building metro systems like the one in Riyadh, as well as switching to alternative fuel sources like several other Arab countries. For example, other countries in this region have banned specific cars from being produced and imported. Combining that with the metro system in Riyadh would also pave the way for making the city a sustainable place to live in.

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External links[edit | edit source]

  • [1] (to view some of the images discussed in this article)



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Asif M., Growth and sustainability trends in the buildings sector in the GCC region with particular reference to the KSA and UAE, Retrieved September 21, 2015, doi: 10.1016/j.rser.2015.05.042

Kaysi I. and Chaaban F.B., Sustainable Transportation in the Arab World: International Benchmarking on Sustainable Transport Policies and their Impacts, Retrieved October 29, 2015

Koushki P. et al, Urban Traffic Noise in Riyadh, Saudi Arabia: Perceptions and Attitudes, Retrieved September 21, 2015, doi: 10.1061/(ASCE)0733-947X(1993)119:5(751)

Lelieveld J. et al, Severe ozone air pollution in the Persian Gulf region, Retrieved September 21, 2015, doi: 10.5194/acp-9-1393-2009

Modaihsh A.S., Characteristics and composition of the falling dust sediments on Riyadh city, Saudi Arabia, Retrieved September 21, 2015, doi: 10.1006/jare.1996.0225

“Total in Use”, OICA, OICA, 2013. Web. November 2015

“Riyadh Metro”, Bechtel, Bechtel, 2014. Web. 21 September 2015

“Riyadh Metro poses technical challenges to contractors”, Arab News, Arab News, 18 October 2014. Web. 4 November 2015

“Six lines by 2019”, Metros & Light Rail, Riyadh, Metros & Light Rail, Riyadh. 2014. Web. 21 September 2015

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