Methane oxidation

Under normal circumstances, methane is relatively stable and does not react with strong oxidising agents such as potassium permanganate, nor does it react with strong acids or strong bases. However, under specific conditions, methane can undergo certain reactions.

At room temperature, it can react under the influence of light; when the reaction is photo-initiated, the absorption of a single photon can produce several thousand chloromethane molecules; if oxygen or impurities capable of trapping free radicals are present, the reaction undergoes an induction period, the duration of which depends on the concentration of these impurities.

Under high-temperature combustion conditions, NOx exists primarily in the form of NO; initially, NO accounts for approximately 95 per cent of the emitted NOx. However, NO reacts very readily with atmospheric oxygen to form NO₂, and therefore NOx in the atmosphere generally exists in the form of NO₂. NO and NO₂ in the air undergo photochemical reactions, converting into one another until an equilibrium is reached.

At higher temperatures or in the presence of clouds or fog, NO₂ reacts further with water molecules to form nitric acid (HNO₃), the second most important acid component in acid rain. In the presence of a catalyst, and under suitable meteorological conditions, the rate at which NO₂ is converted into nitric acid accelerates. In particular, when NO₂ and SO₂ are present simultaneously, they can act as catalysts for one another, resulting in a faster formation of nitric acid.

Furthermore, NOx concentrations can increase as a result of gradual accumulation caused by emissions from aircraft in the stratosphere. NOx then reacts with O₃ in the stratosphere to produce NO and O₂; NO subsequently reacts with O₃ to form NO₂ and O₂, thereby disrupting the O₃ equilibrium, reducing O₃ concentrations and leading to the depletion of the ozone layer.

A range of online analytical instruments—including those for methane oxidation, the degradation of formaldehyde and benzene compounds, carbon dioxide reduction, and the reduction of NOx emissions—primarily utilise mass spectrometers as monitoring and analytical tools.