Question

What are the harmful effects of photochemical smog and how can they be controlled?

Answer 1

Photochemical smog is a type of smog produced when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere. It is visible as a brown haze, and is most prominent in densely populated, warm cities. Think of the components of photochemical smog. Identify the source of the pollutants and methods by which it can be controlled.
Complete step by step answer:
Photochemical smog is formed when pollutants like hydrocarbons and nitric oxide interact with sunlight to form chemicals like $N{O_2}$, Peroxyacyl nitrate (PAN), ozone, acrolein and formaldehyde. Nitrogen dioxide formed is a brown gas which contributes to the haze.
Harmful effects of photochemical smog
The components of photochemical smog are ozone, nitric oxide, acrolein, formaldehyde and peroxyacyl nitrate (PAN). It affects our health and also causes damage to industrial materials
Both ozone and PAN cause eye irritations. Ozone and nitric oxide (NO) can irritate the nose and throat and their high concentration causes a headache, chest pain, dryness of the throat, cough and difficulty in breathing.
Photochemical smog leads to cracking of rubber and extensive damage to plant life. It also causes corrosion of metals, stones, building materials, rubber and painted surfaces.
Controlling photochemical smog
To control or reduce the formation of photochemical smog, we need to control the primary precursors such as NO2 and hydrocarbons, the secondary precursors such as ozone and PAN. The main source of these pollutants is from automobile exhaust. By using catalytic converters in the automobiles, the release of nitrogen oxide and hydrocarbons can be prevented. A catalytic converter uses a reduction catalyst composed of platinum and rhodium. It helps reduce nitrogen oxides by removing nitrogen atoms from nitrogen oxide molecules (NO and $N{O_2}$). This lets the free oxygen form oxygen gas. Then, the nitrogen atoms attached to the catalyst react with each other. This reaction creates nitrogen gas $\left( {{N_2}} \right)$.
Plants like Pinus, Juniperus, Quercus, Pyrus can metabolize $N{O_2}$ and their plantations could help to reduce the formation of photochemical smog.

Note: There are two types of smog- classical smog (reducing smog/London smog) and photochemical smog (oxidizing smog). Photochemical smog is also known as “Los Angeles smog” as it first came into prominence there.
Rubber cracking is due to the ozone produced during the formation of photochemical smog.
PAN is a secondary pollutant. It is not directly emitted as automobile exhaust. It is a lachrymatory substance, meaning that it irritates the lungs and eyes.