7.2 Photochemical Smog

• What is photochemical smog?

  Air pollution from sunlight reactions
• Photochemical smog occurs when sunlight reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs) to create ozone ($O_{3}$) and peroxyacetyl nitrates (PANs), which are secondary pollutants
• What are the primary pollutants involved in photochemical smog formation?

  Nitrogen oxides and VOCs
• Steps in the chemical reactions leading to photochemical smog

  1️⃣ NOx and VOCs are emitted

  2️⃣ Sunlight photolyzes NO2 to NO and O

  3️⃣ Atomic oxygen combines with O2 to form ozone

  4️⃣ VOCs react with NOx to form PANs
• Sunlight acts as a catalyst in the formation of photochemical smog.
• What are the secondary pollutants formed in photochemical smog?

  Ozone and PANs
• Photochemical smog can cause respiratory problems and eye irritation
• Photochemical smog has no environmental impacts.

  False
• In which regions is photochemical smog commonly prevalent?

  Urban areas with traffic
• Strategies to reduce photochemical smog include reducing vehicle emissions and using cleaner energy
• Key factors contributing to photochemical smog

  1️⃣ Emissions of NOx and VOCs

  2️⃣ Reaction with sunlight

  3️⃣ Formation of secondary pollutants
• Photochemical smog is a primary pollutant itself.

  False
• What is the chemical formula for ozone, a secondary pollutant in photochemical smog?

  $O_{3}$
• Match the primary pollutant with its primary source:

  Nitrogen oxides (NOx) ↔️ Vehicle emissions

  Volatile organic compounds (VOCs) ↔️ Industrial solvents
• Photochemical smog forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight
• Steps in the chemical reactions leading to ozone formation in photochemical smog

  1️⃣ NO2 absorbs sunlight and breaks down to NO and O

  2️⃣ Atomic oxygen combines with O2 to form O3

  3️⃣ Ozone reacts with NO to reform NO2
• What are peroxyacetyl nitrates (PANs)?

  Irritant secondary pollutants
• Meteorological conditions like temperature inversions can worsen photochemical smog.
• What role does sunlight play in photochemical smog?

  Catalyzes chemical reactions
• Match the primary pollutant with its main source:

  Nitrogen oxides (NOx) ↔️ Vehicle engines

  Volatile organic compounds (VOCs) ↔️ Industrial solvents
• Photochemical smog primarily occurs in urban areas with heavy traffic and industrial activity
• The photolysis of NO2 is the first step in photochemical smog formation.
• Steps in the chemical reactions leading to PAN formation

  1️⃣ VOCs react with NOx

  2️⃣ PANs are formed as secondary pollutants
• What is the role of ozone destruction in photochemical smog?

  Reverts ozone to NO2
• What happens during the photolysis of nitrogen dioxide?

  $NO_{2} +$$Sunlight \rightarrow NO +$$O$
• Atomic oxygen combines with molecular oxygen to form ozone
• What happens during the destruction of ozone by nitric oxide?

  O_{3} + NO \rightarrow NO_{2} + O_{2}</latex>
• VOCs react with NOx to produce more NO2 without consuming ozone.
• Which meteorological conditions trap pollutants, exacerbating photochemical smog?

  Temperature inversions and calm winds
• Photochemical smog is a type of air pollution formed in urban areas with heavy traffic and industrial activity
• What role does sunlight play in the formation of photochemical smog?

  It acts as a catalyst
• What happens to nitrogen dioxide when exposed to sunlight in the photolysis process?

  NO_{2} + Sunlight \rightarrow NO + O</latex>
• Ultraviolet (UV) radiation is particularly effective in breaking down nitrogen dioxide
• Why is sunlight essential for the formation of photochemical smog?

  Without it, smog cannot develop
• Match the secondary pollutants with their descriptions:

  Ozone (O3) ↔️ A highly reactive gas causing respiratory problems

  Peroxyacetyl nitrates (PANs) ↔️ Potent irritants contributing to smog's toxicity
• What are the primary pollutants that react to form secondary pollutants in photochemical smog?

  Nitrogen oxides (NOx) and VOCs
• Ozone is a highly reactive gas that can cause respiratory problems
• Peroxyacetyl nitrates (PANs) are potent irritants that contribute to the toxicity of photochemical smog.
• What is the overall reaction for the formation of photochemical smog?

  NOx + VOCs + Sunlight \rightarrow O_{3} + PANs</latex>
• Define photochemical smog.

  Air pollution formed by NOx, VOCs, and sunlight