Environmental Impacts of Natural Gas
Global warming emissions
Natural gas is a fossil fuel, though the global warming emissions from its combustion are much lower than those from coal or oil.
Natural Gas 101
Natural gas emits 50 to 60 percent less carbon dioxide (CO2) when combusted in a new, efficient natural gas power plant compared with emissions from a typical new coal plant [1]. Considering only tailpipe emissions, natural gas also emits 15 to 20 percent less heat-trapping gases than gasoline when burned in today’s typical vehicle [2].
Emissions from smokestacks and tailpipes, however, do not tell the full story.
The drilling and extraction of natural gas from wells and its transportation in pipelines results in the leakage of methane, primary component of natural gas that is 34 times stronger than CO2 at trapping heat over a 100-year period and 86 times stronger over 20 years [3]. Preliminary studies and field measurements show that these so-called “fugitive” methane emissions range from 1 to 9 percent of total life cycle emissions [4].
Whether natural gas has lower life cycle greenhouse gas emissions than coal and oil depends on the assumed leakage rate, the global warming potential of methane over different time frames, the energy conversion efficiency, and other factors [5]. One recent study found that methane losses must be kept below 3.2 percent for natural gas power plants to have lower life cycle emissions than new coal plants over short time frames of 20 years or fewer [6]. And if burning natural gas in vehicles is to deliver even marginal benefits, methane losses must be kept below 1 percent and 1.6 percent compared with diesel fuel and gasoline, respectively. Technologies are available to reduce much of the leaking methane, but deploying such technology would require new policies and investments [7].
Air pollution
Cleaner burning than other fossil fuels, the combustion of natural gas produces negligible amounts of sulfur, mercury, and particulates. Burning natural gas does produce nitrogen oxides (NOx), which are precursors to smog, but at lower levels than gasoline and diesel used for motor vehicles. DOE analyses indicate that every 10,000 U.S. homes powered with natural gas instead of coal avoids the annual emissions of 1,900 tons of NOx, 3,900 tons of SO2, and 5,200 tons of particulates [7]. Reductions in these emissions translate into public health benefits, as these pollutants have been linked with problems such as asthma, bronchitis, lung cancer, and heart disease for hundreds of thousands of Americans [9].
However, despite these benefits, unconventional gas development can affect local and regional air quality. Some areas where drilling occurs have experienced increases in concentrations of hazardous air pollutants and two of the six “criteria pollutants” — particulate matter and ozone plus its precursors — regulated by the EPA because of their harmful effects on health and the environment [9]. Exposure to elevated levels of these air pollutants can lead to adverse health outcomes, including respiratory symptoms, cardiovascular disease, and cancer [11]. One recent study found that residents living less than half a mile from unconventional gas well sites were at greater risk of health effects from air pollution from natural gas development than those living farther from the well sites [12].
选择“Disable on www.wenxuecity.com”
选择“don't run on pages on this domain”
