Natural gas is the cleanest of all the fossil fuels. Composed primarily of methane, the main products of the combustion of natural gas are carbon dioxide and water vapor, the same compounds we exhale when we breathe. Coal and oil are composed of much more complex molecules, with a higher carbon ratio and higher nitrogen and sulfur contents. This means that when combusted, coal and oil release higher levels of harmful emissions, including a higher ratio of carbon emissions, nitrogen oxides and sulfur dioxide. Coal and fuel oil also release ash particles into the environment, substances that do not burn but instead are carried into the atmosphere and contribute to pollution. The combustion of natural gas, on the other hand, releases very small amounts of sulfur dioxide and nitrogen oxides, virtually no ash and lower levels of carbon dioxide, carbon monoxide and other reactive hydrocarbons. The chart below is based on the Environmental Protection Agency’s data and shows fossil fuel emission levels for 2010.

Pollutants emitted in the United States, particularly from the combustion of fossil fuels, have led to the development of many pressing environmental problems. Natural gas, emitting fewer harmful chemicals into the atmosphere than other fossil fuels, can help to mitigate some of these environmental issues. These issues include greenhouse gas emissions, smog, air quality and acid rain, industrial and electric generation emissions and pollution from natural gas vehicles.

The use of CNG not only helps the environment, but it is also economically wiser as well. One of the biggest advantages CNG provides is an affordable price. As the world continues to experience ongoing hikes in the cost of gasoline, the low price of CNG offers a glimmer of hope. CNG is typically at least 30 percent cheaper than gasoline. Natural gas vehicles have been introduced in a wide variety of commercial applications, from light-duty trucks and sedans such as taxicabs, package delivery vans, postal vehicles, transit buses, street sweepers and even school buses. In California, transit agency buses are some of the most visible CNG vehicles. Below is a chart from the U.S. Department of Energy showing the difference in prices between gasoline, diesel and CNG.

U.S. Department of Energy Alternative Fuel Comparison Jan-March 2011
	Nationwide Average Price for Fuel	Nationwide average Price for Fuel 4th Quarter 2010
Gasoline (regular)	$3.69	$3.08
Diesel	$4.04	$3.45
CNG	$2.06	$1.93

As you can see, the margin between the price of gasoline and CNG is significant and is clearly more efficient.

Cities now are jumping on the bandwagon and changing things so they can be classified as a “clean city.” Several cities have gone to great measures to help them become more economically friendly. For example, Kansas City, Mo., is well on its way to a green future with the guidance of Kelly Gilbert, the Kansas City Clean Cities Coalition director. Although she has only had this job for a few months, she is off to an exceptional start. She has spearheaded an ambitious proposal that led to a $15 million American Recovery and Reinvestment Act award. This grant provides the funding for the installation of 27 alternative fueling stations as well as the development of about 350 alternative fuel and advanced technology vehicles. Along with 17 partners, she created the Midwest Region Alternative Fuels Project.

Another city showing great success is Grand Ledge, Mich. The GLACC (Greater Lansing Area Clean Cities) is reducing local petroleum consumption by engaging local school district bus fleets. Since 2007, they have been promoting their Clean the Air for School Kids program, which informs local school districts about school bus emission and encourages them to reduce school bus idle time, use cleaner fuels and install emission solutions. They have also worked with the statewide school bus company to eplace older buses with cleaner, more efficient buses and to install emission solutions on nearly 300 buses that carry 10,000 special education students and 5,000 general education students daily. This accomplishment earned GLACC more than $1 million in American Recovery and Reinvestment Act funding to expand the program given by the Environmental Protection Agency National Clean Diesel Funding Assistance Program. For the 2010-2011 school year, this program advanced further by replacing even more buses.

A less intense way in which cities are trying to help go toward a green future is by campaigning. In San Francisco, the American Lung Association and San Francisco Clean Cities partnered together to conduct a three-month idle reduction campaign at six area elementary schools. Idling contributes to outdoor air pollution, is linked to increases in indoor air pollution, stunts children’s lung developments and also wastes fuel. The goals of this campaign, called “Turn Off Your Engines: Idling Wastes Money and Hurts Children,” were to inform drivers about the costs of idling in school zones and to persuade them to change their behavior. With permission, representatives observed driver behavior at each site for 36 hours over a two-week period. They timed how long drivers idled their vehicles and compiled vehicle make and type data. One out of every four drivers idled for more than 30 seconds, while some idled foras long as 10 minutes. The next week, they created fl yers and passed them out with facts about idling, such as idling for 10 minutes a day wastes about $200 worth of fuel a year. This project might not be as big as the one in Kansas City but informing the public of certain dangers of everyday things can help lead a city to becoming “clean.”

Tennessee Cities
Knoxville was recently ranked by the Asthma and Allergy Foundation of America as the fourth worst city in the United States for asthmatics. Events to help the community raise awareness about air quality issues are critical to this region due to the statistics. For the past seven years, the East Tennessee Clean Fuels Coalition has hosted the Run for Clean Air in Knoxville. The participants enjoy a live band, food, prizes and the opportunity to drive and ride in hybrid vehicles.

In the city of Bristol, officials accepted the green challenge and began efforts to reduce the city’s carbon footprint and overall environmental impact in order to create a more livable and responsible community. Bristol understands that “Going Green” is a continual process. Each year, Bristol commits to being more environmentally responsible and pledges to help make the process easy for the public to embrace as well. Bristol has developed a “Going Green” website, which contains a collection of resources and information from the world’s leading environmental experts to help others start their own green lifestyle. The Bristol organizers emphasize that the program helps ensure a safe and beautiful community for generations to come.

In Gatlinburg, the Chamber of Commerce initiated a voluntary program for businesses working to reduce their environmental impact to preserve the natural beauty of this tourism center. Businesses receive information on products and actions to help them achieve green goals. In addition, the city uses biodiesel for its trolleys and LED lights for its holiday display.

Another city heavily involved in becoming greener is Nashville. Nashville created the Green Ribbon Committee, with its goal to become the greenest city in the Southeast. Award-winning Metro Parks Nature Centers work to increase environmental education and outdoor recreation areas. Pervasive programs are cropping up to take Tennessee into a greener future, including Adopt-a-Highway, TVA’s environmental partnerships, Tennessee’s Biofuels Initiative and land acquisition for further development of Tennessee parks.

CNG Station Siting Tips
There is clearly a need to develop the infrastructure for CNG fueling stations in Tennessee. Selecting the right configuration is critical to success. According to Energy International, a global energy consulting firm, the main considerations in choosing a station are the number and type of vehicles fueled and their fueling pattern. Secondary considerations include location, potential future growth, and permitting restrictions. The CNG Station Guide is available online at http://www.afdc.energy.gov/fuels/natural_gas_stations.html [1].

CNG Station Types
Energy International outlines four major station types:

Time-Fill Stations fill vehicles over a six- to eight-hour period. Compressors compress natural gas from pipeline pressure (5–100 psi) to the required vehicle pressure (2,400–3,600 psi) and dispense it into multiple vehicles simultaneously. These stations are best for vehicles such as school buses and utility trucks that return to a central location and can fuel while parked for an extended period. Among all options, they are least expensive to build and staff and require no full-time attendant. Extended fueling time is needed, however, because time-fill stations have relatively small compressors and no CNG storage.

Cascade Fast-Fill Stations provide fast and convenient fueling similar to that provided by conventional liquid fuel stations. CNG storage vessels arranged in cascades, or banks, are used to quickly fill vehicles during peak fueling times, when the compressors alone cannot meet demand. During offpeak times, the compressors refi ll the CNG storage cascades. These stations are suitable for fueling light-duty vehicles at public access stations where use patterns are random. They also are suitable for fueling fleets of light-duty vehicles, such as taxis and police cars, which require a fast-fill and have peak fueling periods. Cascade fast-fill stations are not appropriate for continuous, high-volume fueling because the compressors are not large enough to provide a fast fill once the CNG storage has been depleted. Most of the several hundred public access CNG stations in North America use a cascade fast-fill system.

Buffered Fast-Fill Stations provide fast, continuous, high-volume fueling. Relatively large compressors run continuously during fueling, filling ;vehicles and, in the interval between vehicles, a CNG storage buffer. The storage buffer provides CNG to vehicles at the beginning of the fueling cycle and allows the compressor to run for long periods. Unlike CNG storage in cascade fast-fill systems, buffer storage is not separated into separate banks. Buffered fast-fill stations are suitable for quickly fueling large numbers of heavy-duty, high-fuel capacity vehicles, such as transit buses.

Vehicle Refueling Appliances (VRAs) are like small time-fill stations, containing a small compressor and other equipment within a single unit. VRAs use natural gas from low-pressure pipelines found in many homes and businesses and require 220-volt, single-phase electricity. They are suitable for fueling individual vehicles over an extended period. Grouping multiple VRAs together and adding a cascade storage system provides small- to medium-sized light-duty fleets with fast-fill fueling. VRAs will soon be available for residential installation.

Infrastructure Resources
AFDC Infrastructure Section – New addition to the Alternative Fuels Data Center provides info on equipment and installation, codes and standards, fuel providers, safety, training, success stories and contacts. Link to industry groups such as DOE’s Natural Gas Vehicle Technology Forum. http://en.openei.org/wiki/Alternative_Fuels_and_Advanced_Vehicles_Data_Center [2].

Clean Cities Tiger Teams – Created to help coalitions overcome AFV and infrastructure challenges, with experts from various technical disciplines. Part of the Clean Cities Technical Assistance Program. http://www1.eere.energy.gov/cleancities/technical_assistance.html [3].

CNG Station Guide – Free online guide helps prospective and existing station owners build and operate efficient and cost-effective facilities. http://www1.eere.energy.gov/cleancities/pdfs/ngv_wkshp_adams.pdf [4].

For More About Clean Fuels, see http://www1.eere.energy.gov/cleancities/publications.html [5].

Federal and State Laws and Incentives: http://www.afdc.energy.gov/laws/ [6].

References
[1] Cognan, Ron. “Natural Gas: The Proven Alternative Fuel.” Green Car Journal. 2009: 1-11.

[2] Cognan, Ron. “Natural Gas: Driving a Cleaner and More Secure Future.” Green Car Journal. 2010: 1-9.

[3] “Compressed Natural Gas (CNG) As A Transportation Fuel.” California Energy Commission: Consumer Energy Center. (2010): 1-6.

[4] Smith, Dennis, and Linda Bluestein. “Clean Cities Now.” U.S. Department of Energy: Energy Efficiency & Renewable Energy. 14.2 (2010): 1-8.

[5] “Tennessee Gets Serious About Natural Gas.” Tennessee Clean Fuels Advisor. 2011: 1-4.