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2022.12.09
カテゴリ： カテゴリ未分類
地球温暖化ガスといえば二酸化炭素が知られているが、その他にもいくつかの温暖化ガスがあり、よく知られているのはメタンである。そもそも温暖化の機構は大気中の気体が太陽光の赤外線を吸収して地球を暖めることによる。大気の主成分は窒素と酸素だが、赤外線の吸収能は小さい。大気には色んな気体が放出されるが、ほとんどが短い時間で分解されて、主に二酸化炭素になっている。分解されず長期間大気中に留まるのがメタンやフロンで、これが温暖化ガスである。メタンは赤外線の吸収能が二酸化炭素より大きいので、量が少なくても温暖化効果は大きく、現在の地球温暖化への寄与は30％近いという。メタンの主発生源は天然ガス等の化石燃料、農業、廃棄物だという。このうち農業は規制が難しそうだが、廃棄物は酸素の少ない状態で堆積すると微生物発酵してメタンができるので、廃棄方法を工夫すれば改良できるのではないだろうか。アメリカではセールオイルとセールガスの生産でメタンが出ていると聞いた。排出規制があって、回収して販売するか燃すことになっているが、リークや不完全燃焼で技術的に難しいようで、規制は十分に守られていないと報道されている。メタンは燃やすと二酸化炭素になるがメタンのままよりはよいし、一緒に排出される他の炭化水素ガスより体積当たりの二酸化炭素の発生量は少ない。
In addition to carbon dioxide several gases have been known as greenhouse gas. Methane is one of them. Global warming is caused by solar infrared light trapped by those gases released into the atmosphere. The air is composed of nitrogen and oxygen, but these two inorganic gases have very little absorbability of infrared light. In the mean time, many gases are released into the atmosphere, and most of them trap more infrared light than carbon dioxide. But they are degraded in the air for short time. Greenhouse gas such as methane and freon are stable and remained undegraded, thus causing global warming. Despite smaller presence of methane in the air than carbon dioxide, methane is responsible for 30 % of global warming.
The main emitters of methane are fossil fuel industry, farming and landfill. I think regulating CO2 emission is tough for farming, but it is possible to reduce the emission from the other two emitters. Shale oil industry is a significant methane emitter in the US. Operators of its well are supposed to recover or burn leaked hydrocarbon gases including methane under the US federal law. But the regulation is not followed closely. Methane emission is rising globally.
In addition to carbon dioxide several gases have been known as greenhouse gas. Methane is one of them. Global warming is caused by solar infrared light trapped by those gases released into the atmosphere. The air is composed of nitrogen and oxygen, but these two inorganic gases have very little absorbability of infrared light. In the mean time, many gases are released into the atmosphere, and most of them trap more infrared light than carbon dioxide. But they are degraded in the air for short time. Greenhouse gas such as methane and freon are stable and remained undegraded, thus causing global warming. Despite smaller presence of methane in the air than carbon dioxide, methane is responsible for 30 % of global warming.
The main emitters of methane are fossil fuel industry, farming and landfill. I think regulating CO2 emission is tough for farming, but it is possible to reduce the emission from the other two emitters. Shale oil industry is a significant methane emitter in the US. Operators of its well are supposed to recover or burn leaked hydrocarbon gases including methane under the US federal law. But the regulation is not followed closely. Methane emission is rising globally.
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