Multiple choice

Which of these pollutants are responsible for photochemical smog formed in congested metropolitan cities?

  1. Ozone peroxyacetyl nitrate and NOx

  2. Smoke, peroxyacetyl nitrate and SO2

  3. Hydrocarbons, SO2 and CO2

  4. Hydrocarbons, ozone and SOx

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A Correct answer
Explanation

Photochemical smog was reported in Los Angeles. This oxidising type of pollution is characterised by the presence of large concentration of ozone, oxides of nitrogen and various hydrocarbons.

Nitric oxide (NO) is formed by reaction between oxygen and nitrogen.

NO reacts with air forming NO2.

NO2 absorbs light and nitric oxide and nascent oxygen [O] are formed.

Nascent oxygen combines with molecular oxygen to form ozone.

Ozone reacts with unburnt hydrocarbons to give aldehydes and ketone.

Nitrogen oxides, oxygen and ketone give rise to PAN.