Under normal conditions, most of the solar radiation reaching the Earth’s surface is radiated back toward space. However, atmospheric greenhouse gases—like CO2 , CH4 , and ozone—can trap this energy and prevent the heat from escaping, somewhat like the glass panels of a greenhouse. Greenhouse gases (GHGs) are necessary to life as we know it because they keep the planet’s surface warmer than it would otherwise be. However, as the concentrations of these gases continue to increase in the atmosphere, largely due to the burning of fossil fuels like coal and oil, the Earth’s temperature is climbing above past levels. Such changes in temperature, along with changes in precipitation and other weather conditions due to climate change, may lead to even higher air pollution levels. In addition to GHGs, other pollutants contribute to climate change. Black carbon (BC), a component of particle pollution, directly absorbs incoming and reflected solar radiation and reduces reflection of sunlight off of snow and ice. In these ways, BC contributes to increased absorption of energy at the Earth’s surface and warming of the atmosphere. Recent studies suggest that BC may be having a significant impact on the Earth’s climate. Other types of particles—particularly sulfates, nitrates, and some types of directly emitted organic carbon—are largely reflective and therefore have a net cooling impact on the atmosphere. Particles can also have important indirect effects on climate through impacts on clouds and precipitation. The longer a pollutant stays in the atmosphere, the longer the effect associated with that pollutant will persist. Some climate forcing pollutants stay in the atmosphere for decades or centuries after they are emitted, meaning today’s emissions will affect the climate far into the future. These pollutants, like CO2 , tend to accumulate in the atmosphere so their net warming impact continues over time. Other climate forcers, such as ozone and BC, remain in the atmosphere for shorter periods of time so reducing
emissions of these pollutants may have beneficial impacts on climate in the near term. These short-lived climate forcers originate from a variety of sources, including the burning of fossil fuels and biomass, wildfires, and industrial processes. Short-lived climate forcing pollutants and their chemical precursors can be transported long distances and may produce particularly harmful warming effects in sensitive regions such as the Arctic. sources of air PoLLution Air pollution consists of gas and particle contaminants that are present in the atmosphere. Gaseous pollutants include SO2 , NOx , ozone, carbon monoxide (CO), volatile organic compounds (VOCs), certain toxic air pollutants, and some gaseous forms of metals. Particle pollution (PM2.5 and PM10) includes a mixture of compounds. The majority of these compounds can be grouped into five categories: sulfate, nitrate, elemental (black) carbon, organic carbon, and crustal material. Some pollutants are released directly into the atmosphere. These include gases, such as SO2 , and some particles, such as crustal material and elemental carbon. Other pollutants are formed in the air. Ground-level ozone forms when emissions of NOx and VOCs react in the presence of sunlight. Similarly, some particles are formed from other directly emitted pollutants. For example, particle sulfates result from SO2 and ammonia (NH3) gases reacting in the atmosphere. Weather plays an important role in the formation of secondarily formed air pollutants, as discussed later in the Ozone and Particle Pollution sections. EPA tracks direct emissions of air pollutants and emissions that contribute to the formation of key pollutants, also known as precursor emissions. Emissions data are compiled from many different organizations, including industry and state, tribal, and local agencies. Some emissions data are based on actual measurements while others are estimates. Generally, emissions come from large stationary fuel combustion sources (such as electric utilities and industrial boilers), industrial and other processes (such as metal smelters, petroleum refineries, cement kilns, manufacturing facilities, and solvent utilization), and mobile sources including highway vehicles and non-road sources (such as recreational and construction equipment, marine vessels, aircraft, and locomotives). Sources emit different combinations of pollutants. For example, electric utilities release SO2 , NOx , and particles. Figure 2 shows the distribution of national total emissions estimates by source category for specific pollutants in 2008. Electric utilities contribute about 70 percent of national SO2 emissions. Agricultural operations (other processes) contribute over 80 percent of national NH3 emissions. Almost 50 percent of the
Figure 2. Distribution of national total emissions estimates by source category for specific pollutants, 2008.
national VOC emissions originate from solvent use (other processes) and highway vehicles. Highway vehicles and non-road mobile sources together contribute approximately 80 percent of national CO emissions. Pollutant levels differ across regions of the country and within local areas, depending on the size and type of sources present. Fossil fuel combustion is the primary source contributing to CO2 emissions (not shown in Figure 2). In 2007 (the most recent year for which data are available), fossil fuel combustion contributed almost 94 percent of total CO2 emissions (source: http:// epa.gov/climatechange/emissions/usinventoryreport. html). Major sources of fossil fuel combustion include electricity generation, transportation (including personal and heavy-duty vehicles), industrial processes, residential, and commercial. Electricity generation contributed approximately 42 percent of CO2 emissions from fossil fuel combustion while transportation contributed approximately 33 percent. Primary sources of CH4 emissions (not shown) include livestock, landfills, and natural gas systems (including wells, processing facilities, and distribution pipelines). In 2007, these sources contributed about 64 percent of total U.S. CH4 emissions. Other contributing sources include coal mining (10 percent) and manure management (8 percent).
ภายใต้เงื่อนไขปกติ ส่วนใหญ่ของรังสีแสงอาทิตย์ถึงพื้นผิวของโลกเป็น radiated กลับไปทางพื้นที่ อย่างไรก็ตาม ก๊าซเรือนกระจกอากาศ — เช่น CO2, CH4 และโอโซนซึ่งสามารถดักพลังงานนี้ และป้องกันความร้อนจากการหลบหนี ค่อนข้างเช่นแผงกระจกของเรือนกระจก ก๊าซเรือนกระจก (GHGs) จำเป็นเพื่อชีวิตเรารู้มันเนื่องจากพวกเขาที่ทำให้พื้นผิวของดาวเคราะห์ที่อุ่นกว่าที่อื่นจะ อย่างไรก็ตาม เป็นความเข้มข้นของก๊าซเหล่านี้ยังคงเพิ่มขึ้นในบรรยากาศ ส่วนใหญ่เนื่องจากการเผาเชื้อเพลิงฟอสซิลเช่นถ่านหินและน้ำมัน อุณหภูมิของโลกจะปีนเหนือระดับที่ผ่านมา เปลี่ยนแปลงอุณหภูมิ พร้อมกับฝนและสภาพอื่น ๆ เนื่องจากการเปลี่ยนแปลงสภาพภูมิอากาศ การเปลี่ยนแปลงอาจทำให้ระดับมลพิษทางอากาศสูงขึ้น นอกจาก GHGs สารมลพิษอื่น ๆ นำไปสู่การเปลี่ยนแปลงสภาพภูมิอากาศ คาร์บอนสีดำ (BC), ส่วนประกอบของอนุภาคมลพิษ ดูดซับเข้า และสะท้อนรังสีแสงอาทิตย์โดยตรง และลดการสะท้อนแสงแดดออกหิมะและน้ำแข็ง วิธีเหล่านี้ BC จัดสรรไปเพิ่มการดูดซึมพลังงานที่พื้นผิวของโลกและภาวะโลกร้อนของบรรยากาศ การศึกษาล่าสุดแนะนำว่า BC อาจมีผลกระทบสำคัญในบรรยากาศของโลก อนุภาคชนิดอื่น — sulfates อย่างยิ่ง nitrates และบางชนิดโดยตรงออกคาร์บอนอินทรีย์ — ส่วนใหญ่สะท้อนแสง และมีสุทธิเย็นในบรรยากาศดังนั้น การ อนุภาคสามารถยังมีความสำคัญทางอ้อมผลอากาศผ่านผลกระทบเมฆและฝน อีกต่อไปเป็นมลพิษอยู่ในบรรยากาศ ผลที่เกี่ยวข้องกับมลพิษที่จะคงอยู่อีกต่อไป สภาพภูมิอากาศบางอย่างบังคับให้พักสารมลพิษในบรรยากาศสำหรับทศวรรษหรือศตวรรษหลังจากที่มีการส่งออก การหมายความว่า วันนี้ปล่อยจะกระทบสภาพภูมิอากาศในอนาคตไกล สารมลพิษเหล่านี้ เช่น CO2 มีแนวโน้มที่สะสมอยู่ในบรรยากาศเพื่อให้ผลร้อนสุทธิต่อช่วงเวลา Forcers อื่น ๆ สภาพภูมิอากาศ โอโซนและ BC ยังคงอยู่ในบรรยากาศสั้นกว่าระยะเวลาที่ลดลงดังนั้น emissions of these pollutants may have beneficial impacts on climate in the near term. These short-lived climate forcers originate from a variety of sources, including the burning of fossil fuels and biomass, wildfires, and industrial processes. Short-lived climate forcing pollutants and their chemical precursors can be transported long distances and may produce particularly harmful warming effects in sensitive regions such as the Arctic. sources of air PoLLution Air pollution consists of gas and particle contaminants that are present in the atmosphere. Gaseous pollutants include SO2 , NOx , ozone, carbon monoxide (CO), volatile organic compounds (VOCs), certain toxic air pollutants, and some gaseous forms of metals. Particle pollution (PM2.5 and PM10) includes a mixture of compounds. The majority of these compounds can be grouped into five categories: sulfate, nitrate, elemental (black) carbon, organic carbon, and crustal material. Some pollutants are released directly into the atmosphere. These include gases, such as SO2 , and some particles, such as crustal material and elemental carbon. Other pollutants are formed in the air. Ground-level ozone forms when emissions of NOx and VOCs react in the presence of sunlight. Similarly, some particles are formed from other directly emitted pollutants. For example, particle sulfates result from SO2 and ammonia (NH3) gases reacting in the atmosphere. Weather plays an important role in the formation of secondarily formed air pollutants, as discussed later in the Ozone and Particle Pollution sections. EPA tracks direct emissions of air pollutants and emissions that contribute to the formation of key pollutants, also known as precursor emissions. Emissions data are compiled from many different organizations, including industry and state, tribal, and local agencies. Some emissions data are based on actual measurements while others are estimates. Generally, emissions come from large stationary fuel combustion sources (such as electric utilities and industrial boilers), industrial and other processes (such as metal smelters, petroleum refineries, cement kilns, manufacturing facilities, and solvent utilization), and mobile sources including highway vehicles and non-road sources (such as recreational and construction equipment, marine vessels, aircraft, and locomotives). Sources emit different combinations of pollutants. For example, electric utilities release SO2 , NOx , and particles. Figure 2 shows the distribution of national total emissions estimates by source category for specific pollutants in 2008. Electric utilities contribute about 70 percent of national SO2 emissions. Agricultural operations (other processes) contribute over 80 percent of national NH3 emissions. Almost 50 percent of the Figure 2. Distribution of national total emissions estimates by source category for specific pollutants, 2008.national VOC emissions originate from solvent use (other processes) and highway vehicles. Highway vehicles and non-road mobile sources together contribute approximately 80 percent of national CO emissions. Pollutant levels differ across regions of the country and within local areas, depending on the size and type of sources present. Fossil fuel combustion is the primary source contributing to CO2 emissions (not shown in Figure 2). In 2007 (the most recent year for which data are available), fossil fuel combustion contributed almost 94 percent of total CO2 emissions (source: http:// epa.gov/climatechange/emissions/usinventoryreport. html). Major sources of fossil fuel combustion include electricity generation, transportation (including personal and heavy-duty vehicles), industrial processes, residential, and commercial. Electricity generation contributed approximately 42 percent of CO2 emissions from fossil fuel combustion while transportation contributed approximately 33 percent. Primary sources of CH4 emissions (not shown) include livestock, landfills, and natural gas systems (including wells, processing facilities, and distribution pipelines). In 2007, these sources contributed about 64 percent of total U.S. CH4 emissions. Other contributing sources include coal mining (10 percent) and manure management (8 percent).
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