Sulfur oxides - Sulfur staghorn fern

[ I ] A general term for sulfur oxides. Seven types are known: disulfur monoxide ( _S2O ), sulfur monoxide (SO), disulfur trioxide ( _{S2O3 )} , sulfur dioxide (SO2 ₎ , sulfur trioxide (SO3 ₎ , disulfur heptaoxide ( _{S2O7 )} , and sulfur tetroxide ( _SO4) . Of these, only sulfur dioxide and sulfur trioxide exist stably under normal conditions. Disulfur monoxide is a compound that exists as a gas under low pressure and is thermodynamically unstable. Sulfur monoxide is produced in a short lifespan when sulfur dioxide is subjected to a glow discharge in the presence of sulfur. It is an intermediate and is easily disproportionated.

3SO → _SO2 + _S2O

It also produces sulfur and sulfur dioxide through thermal decomposition. Sulfur tetroxide is a peroxide of β- _SO3 . [ II ] Sulfur oxides (commonly known as _SOx ) as air pollutants include sulfur dioxide and sulfur trioxide. They are pollutants produced when fuels containing sulfur, such as petroleum and coal, are burned, and the majority of the material produced during the combustion process is generally sulfur dioxide. _SO2 is oxidized in the atmosphere to _SO42- . This conversion proceeds rapidly through photooxidation or contact acid in the presence of _NOx and _O2 , and is self-nucleated to form sulfuric acid mist or is adsorbed on the surface _of fine particles (diameter 1 μm) and exists as ( _NH4 ) ^2SO4 , _CaSO4 , _PbSO4 , and _CdSO4 . Along with nitrogen oxides, it is one of _the substances that cause acid rain, and it affects the human respiratory system and causes the withering of plants such as forests and crops. As a measure to reduce this environmental burden, the use of low-sulfur fuels and the installation of flue gas desulfurization equipment are being promoted.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

【Ⅰ】硫黄の酸化物の総称．一酸化二硫黄S₂O，一酸化硫黄SO，三酸化二硫黄S₂O₃，二酸化硫黄SO₂，三酸化硫黄SO₃，七酸化二硫黄S₂O₇，四酸化硫黄SO₄の7種類が知られている．このうち，通常の条件で安定に存在するのは二酸化硫黄と三酸化硫黄だけである．一酸化二硫黄は低圧下で気体として存在する化合物であり，熱力学的に不安定である．一酸化硫黄は二酸化硫黄を硫黄の存在下にグロー放電をしたときに短寿命で生成する．中間体であり，不均化しやすい．

3SO → SO₂ ＋ S₂O

また，熱分解により硫黄と二酸化硫黄を生成する．また，四酸化硫黄はβ-SO₃の過酸化物である．【Ⅱ】大気汚染物質としての硫黄酸化物(通称ソックスSO_x)は，二酸化硫黄，三酸化硫黄などをさす．石油や石炭など硫黄分を含んだ燃料が燃焼して生じる汚染物質で，一般に燃焼過程で発生する大部分が二酸化硫黄である．SO₂は大気中で酸化されてSO₄^2－になる．この変換はNO_xや O₂ の共存下における光酸化や接触酸ですみやかに進行し，自己核化により硫酸ミストか，微粒子(粒径1 μm)の表面に吸着され，(NH₄)₂SO₄，CaSO₄，PbSO₄，CdSO₄として存在する．窒素酸化物とともに酸性雨の原因物質の一つであり，ヒトの呼吸器に影響を与え，森林や農作物などの植物を枯らす原因ともなっている．こうした環境負荷の軽減対策として，低硫黄燃料の使用や排煙脱硫装置の設置が進められている．

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