Question

Point out the true statement.
(a)- Photochemical smog occurs in a daytime while the classical smog occurs in the morning hours
(b)- Classical smog has an oxidizing character whereas the photochemical smog is reducing in
character
(c)- During formation of smog, the level of ozone in the atmosphere goes down
(d)- Classical smog is good for health but not photochemical smog

Answer 1

Air Pollutants can be solid particles, liquid droplets, or gases. They can be natural or manmade. Smog is a harmful mixture of particulates and gases that is the result of urban air pollution.

Complete step by step solution:

Photochemical smog appears to be a brownish-gray haze which is caused by the action of solar ultraviolet radiation on the atmosphere, which has been polluted with hydrocarbons and oxides of nitrogen. It mainly consists of anthropogenic air pollutants such as ozone, nitric acid, and organic compounds. Nitrogen oxides act as initiators in the appearance of photochemical smog. When nitrogen oxides are emitted from internal combustion engines, it absorbs the visible or ultraviolet energy of sunlight and forms nitric oxide (NO) and free atoms of oxygen (O). This free O atom further combines with molecular oxygen (${{O}_{2}}$) and form ozone (${{O}_{3}}$). In the presence of hydrocarbons (methane being the exception), few other organic compounds, and sunlight, chemical reactions take place, which leads to formation of photochemical smog.
The formation of photochemical smog can be summarized by following chemical equations:

NO+{{O}_{2}}\to N{{O}_{2}}+U.V\to O+NO \\\ O+{{O}_{2}}\to {{O}_{3}} \\\ {{O}_{3}}+NO~\to {{O}_{2}}+N{{O}_{2}} \\\ RC+O~\to ~RCO+{{O}_{2}}\to RC{{O}_{3}} \\\ {{O}_{2}}+RC{{O}_{3}}\to {{O}_{3}}+RC{{O}_{2}} \\\ NO+RC{{O}_{3}}\to N{{O}_{2}}+RC{{O}_{2}} \\\ \end{array}$$ > Photochemical smog has found to occur more often in summer, because we have the most sunlight, which supports its formation. Photochemical smog is also sometimes known as "oxidizing smog", because of the presence of a high concentration of oxidizing agents in it. Ozone is a common photochemical smog and acts as an oxidizing agent. > Classical smog is a form of smog which is a mixture of smoke, fog and sulphur dioxide ($$S{{O}_{2}}$$), commonly found in areas having a cool and humid climate. It acts as a reducing agent in atmospheric pollution and hence, it is also named as reducing smog. > Both types of smog affect human health adversely. Breathing in smog can cause irritation to our eyes, decreases lung's breathing capacity and in severe conditions causes asthma. So, option (a) is correct. **Note:** Ozone ($${{O}_{3}}$$) is the most toxic constituent of photochemical smog, and it has caused considerable damage to agricultural and native plants in many locations. It also affects the environment adversely by slowing the process of photosynthesis.