Discuss in detail the photochemical smog emphasizing its formation, effects and mitigation. Explain the…

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Discuss in detail the photochemical smog emphasizing its formation, effects and mitigation. Explain the 1999 Gothenburg Protocol.

Ghissu Editorial · Accepted Answer

Photochemical smog forms when sunlight drives reactions between nitrogen oxides and VOCs, producing ozone and PAN that harm lungs, crops and materials, and is cut by controlling these precursors. The 1999 Gothenburg Protocol set binding national ceilings for SO2, NOx, VOCs and ammonia, adding PM2.5 in 2012.

**Introduction**

Photochemical smog is an oxidising haze formed when sunlight drives reactions between nitrogen oxides and volatile organic compounds, first seen over Los Angeles in the 1940s and now a summer problem in Indian cities.

**Formation of Photochemical Smog**

SKETCH: flow | How Photochemical Smog Forms
- Vehicles emit NOx, VOCs
- Sunlight splits NO2
- Free O forms O3
- VOCs turn NO into NO2
- Ozone, PAN accumulate

1. **Secondary pollutant**: NO2 splits in sunlight, the freed oxygen atom forms ozone, and VOC radicals keep regenerating NO2 from NO, so ozone, PAN and aldehydes accumulate instead of being consumed.
2. **Conditions**: Strong sunshine, heat, calm air and temperature inversion make ozone peak on summer afternoons.

**Effects and Mitigation**

1. **Health and crops**: Ozone and PAN irritate eyes and airways and worsen asthma, and ozone entering leaf stomata cuts wheat and rice yields.
2. **Materials and climate**: It cracks rubber, causes haze and acts as a short-lived climate pollutant.
3. **Cutting precursors**: Bharat Stage VI norms (2020), vapour recovery at petrol pumps, FAME electric mobility and public transport reduce NOx and VOCs, while GRAP curbs emissions on bad days.

**The 1999 Gothenburg Protocol**

1. **Framework**: Under the UNECE Convention on Long-range Transboundary Air Pollution, it targets acidification, eutrophication and ground-level ozone, in force since 2005.
2. **Ceilings**: It fixed binding national emission ceilings for SO2, NOx, VOCs and ammonia for 2010, treating shared precursors together; the 2012 amendment added PM2.5 for 2020, the first binding particulate limits. India is not a party, but the model suits its airsheds.

**Conclusion**

Photochemical smog proves air quality needs multi-pollutant action; vehicle and fuel reform with Gothenburg-style regional ceilings would protect health and harvests.

Discuss in detail the photochemical smog emphasizing its formation, effects and mitigation. Explain the 1999 Gothenburg Protocol.

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