(صورة توضيحية فقط)
Photochemical smog is formed through a complex series of reactions involving sunlight, nitrogen oxides (NOx), and volatile organic compounds (VOCs). The process is initiated when sunlight splits nitrogen dioxide ([latex]NO_2[/latex]) into nitric oxide (NO) and an oxygen atom (O). This free oxygen atom then combines with molecular oxygen ([latex]O_2[/latex]) to form ground-level ozone ([latex]O_3[/latex]), a primary component of smog.
يُعدّ تكوّن الضباب الدخاني الكيميائي الضوئي عملية دورية مدفوعة بالإشعاع الشمسي. تبدأ الدورة في ساعة الذروة الصباحية، عندما تُطلق المركبات كميات كبيرة من أكاسيد النيتروجين (NOx) والمركبات العضوية المتطايرة (VOCs). ضوء الشمس الأشعة فوق البنفسجية (UV) radiation provides the energy for the initial key reaction: the photolysis of nitrogen dioxide ([latex]NO_2 \\xrightarrow{h\nu} NO + O[/latex]). The highly reactive atomic oxygen (O) then quickly combines with diatomic oxygen ([latex]O_2[/latex]) to form ozone ([latex]O_3[/latex]): [latex]O + O_2 \\rightarrow O_3[/latex]. Normally, this ozone would be destroyed by reacting with the nitric oxide (NO) produced in the first step, reforming [latex]NO_2[/latex] and [latex]O_2[/latex] in a null cycle. However, the presence of VOCs disrupts this balance.
VOCs react with hydroxyl radicals (OH) in the atmosphere to form peroxy radicals ([latex]RO_2[/latex]). These peroxy radicals are highly effective at oxidizing NO to [latex]NO_2[/latex] without consuming an ozone molecule: [latex]RO_2 + NO \\rightarrow RO + NO_2[/latex]. This reaction rapidly regenerates [latex]NO_2[/latex], which can then be photolyzed again to produce more ozone, while also preventing NO from depleting the existing ozone. This leads to a net accumulation of ozone throughout the day, with concentrations typically peaking in the afternoon. The complex mixture also includes other harmful secondary pollutants like peroxyacetyl nitrate (PAN), aldehydes, and nitric acid, creating the characteristic hazy, irritant-laden air known as smog.
الضباب الدخاني الكيميائي الضوئي
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الصور والتنزيلات بالحجم الكامل متاحة فقط، ومجانية تمامًا، للأعضاء المسجلين.
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