Discuss in detail the photochemical smog emphasising its formation, effects and mitigation. Explain the 1999 Gothenburg Protocol. (Answer in 150 words)

Photochemical smog is a secondary pollutant mixture formed when nitrogen oxides and volatile organic compounds react under sunlight, especially in warm, stagnant urban air.

Formation and effects

• Sunlight photolyses nitrogen dioxide, producing ozone; reactions with VOCs generate peroxyacetyl nitrate, aldehydes and oxidants.
• It causes eye and throat irritation, asthma, reduced lung function and plant damage.
• Ozone and PAN reduce crop yields, damage materials and impair visibility.

Control measures

• Control vehicle and industrial NOx and VOC emissions through fuel standards, catalytic converters, public transport and clean energy.
• Prevent evaporative emissions, enforce industrial controls, improve urban ventilation and use real-time monitoring.
• Regional airshed coordination is essential because precursor pollutants travel across boundaries.

Gothenburg Protocol

• The 1999 protocol under the UNECE Convention on Long-Range Transboundary Air Pollution sets emission ceilings for sulphur dioxide, nitrogen oxides, ammonia and VOCs.
• Its multi-pollutant, multi-effect approach addresses acidification, eutrophication and ground-level ozone through national commitments and best available techniques.

Secondary pollutants; NOx; VOCs; ozone; PAN; airshed; UNECE; acidification; eutrophication.