Photochemical smog

(noun)

a type of air pollution formed through solar radiation reacting with airborne pollutants, like nitrogen oxides and volatile organic compounds

Related Terms

Examples of Photochemical smog in the following topics:

  • Photochemical Smog

    • Photochemical smog is a major contributor to air pollution.
    • The components of photochemical smog were established during the 1950s.
    • The mixture of these primary and secondary pollutants forms photochemical smog.
    • Photochemical smog is composed of primary and secondary pollutants.
    • Recall what causes photochemical smog and why it is a problem for humans

  • Photochemistry

    • Two fundamental principles are the foundation for understanding photochemical transformations:
    • The first law of photochemistry, the Grotthuss-Draper law, states that light must be absorbed by a compound in order for a photochemical reaction to take place.
    • The efficiency with which a given photochemical process occurs is given by its Quantum Yield (Φ).
    • Since many photochemical reactions are complex, and may compete with unproductive energy loss, the quantum yield is usually specified for a particular event.
    • The primary photochemical reaction is the homolytic cleavage of a carbon-carbon bond shown in the top equation.

  • Cyclohexadienone Reactions

    • Derivatives of 2,5-cyclohexadienone are common in nature, and their photochemical transformations posed a challenge to early researchers.
    • These photochemical rearrangements occur by way of triplet excited states, which are conveniently depicted as diradicals.
    • Derivatives of 6,6-disubstituted 2,4-cyclohexadienones are also photochemically reactive.
    • Lumisantonin itself undergoes additional solvent dependent photochemical transformations, shown in the bottom part of the diagram.
    • Suggested mechanisms for the photochemical transformation of santonin and the thermal reaction of lumisantonin are shown above in the third diagram.

  • Air Pollution

    • Increased ozone concentrations at ground levels: an increase in surface ozone that contributes to smog.

  • Electrocyclic Reactions

    • Photochemical ring closure can be effected, but the stereospecificity is opposite to that of thermal ring opening.

  • Non-Ionic Reactions

    • The term "pericyclic reaction" encompasses a large and varied group of concerted thermal and photochemical transformations.

  • Alkene Isomerization

    • A photochemical reaction occurs when internal conversion and relaxation of an excited state leads to a ground state isomer of the initial substrate molecule, or when an excited state undergoes an intermolecular addition to another reactant molecule in the ground state.
    • The cis-trans photochemical isomerization of stilbene is a reaction of the first kind, as shown in the first diagram below.

  • Protecting the Environment

    • Engine exhaust from growing numbers of automobiles, for instance, was blamed for smog and other forms of air pollution in larger cities.

  • Mechanistic Background

    • Consequently, ultraviolet light is most often used to effect photochemical change.
    • The light required for a photochemical reaction may come from many sources.
    • Photochemical sensitization commonly occurs by a T1 + S0 → S0 + T1 reaction, where the bold red-colored species is the sensitizer.

  • Perplexing Features of Pericyclic Reactions

    • The thermal reaction is disrotatory, and the photochemical process is conrotatory.