Answer: The peroxyacetyl radical (CH₃C(O)OO•) - formed by OH•-initiated oxidation of hydrocarbons - combines with NO₂ to give PAN; it is a strong lachrymator and, being thermally unstable, decomposes in warmer regions to re-release NO₂, transporting NOx over long distances.
- A PAN forms by direct condensation of SO₂ with little₂ in humid conditions; it hydrolyses to H₂SO₄ and HNO₃, producing acid rain in most observed cases under typical physiological conditions according to standard texts in general clinical practice as frequently documented
- B PAN is primarily released from diesel exhaust, acts as a reducing agent in photochemical smog, and decomposes rapidly in cold climates in most reference accounts under normal conditions as generally observed in typical laboratory settings under usual circumstances
- C The peroxyacetyl radical (CH₃C(O)OO•) - formed by OH•-initiated oxidation of hydrocarbons - combines with NO₂ to give PAN; it is a strong lachrymator and, being thermally unstable, decomposes in warmer regions to re-release NO₂, transporting NOx over long distances
- D PAN forms at night through dark reactions of O₃ with alkenes; it is non-toxic to biological systems but corrodes rubber and metals according to most studies in the majority of documented cases as widely reported in standard reference material under most conditions studied
Correct answer: C. The peroxyacetyl radical (CH₃C(O)OO•) - formed by OH•-initiated oxidation of hydrocarbons - combines with NO₂ to give PAN; it is a strong lachrymator and, being thermally unstable, decomposes in warmer regions to re-release NO₂, transporting NOx over long distances
Explanation: PAN forms via: hydrocarbon + OH• → acetaldehyde → (OH•) → acetyl radical (CH₃CO•) → (O₂) → peroxyacetyl radical (CH₃C(O)OO•) → (NO₂) → PAN. PAN is a potent lachrymator, causing eye tearing, and inhibits photosynthesis at ppb levels. Crucially, PAN is thermally labile: it decomposes at warmer temperatures to release NO₂ again, acting as a long-range transporter of NOx pollution from urban sources to remote rural areas.
Classical smog is a reducing mixture of SO₂ and fog, while photochemical smog is an oxidising mixture generated by UV-driven reactions of NOx and hydrocarbons.
Concept context
Understand how human activities alter the atmosphere, water, and soil. Covers air pollutants, smog types, ozone depletion, acid rain, greenhouse effect, water and soil pollution, and the principles of green chemistry.