Question

Which one of the following contains secondary pollutants?
(a)Automobile exhaust
(b)Chimney smoke
(c)Photochemical smog
(d)Classical smog

Answer 1

Hint: It is formed when the sun's ultraviolet light reacts with nitrogen oxides in the atmosphere. It is noticeable as a brown haze and is most prevalent in the morning and afternoon, particularly in densely populated, warm cities.

Complete answer:
The photochemical reaction is caused by energy absorption in the form of light. The term smog is made up of smoke and smog. Photochemical smog is the main contributor to air pollution and consists of primary and secondary contaminants. Mainly nitrogen oxides and volatile organic compounds such as unsaturated hydrocarbons are those which have double or triple covalent bonds between adjacent carbon atoms. For example, ethylene.
The main undesired components of photochemical smog are nitrogen dioxide (${ NO }_{ 2 }$ ), ozone (${ 0 }_{ 3 }$), PAN (peroxyacetyl nitrate), and chemical compounds containing the – CHO group (aldehydes). PAN and aldehydes can cause eye irritation and plant damage if their concentrations are too high.

Additional Information: Exhaust gas or flue gas is produced as a result of the combustion of fuels such as natural gas, gasoline, petrol, biodiesel blends, diesel, fuel oil, or coal. Depending on the form of the engine, the exhaust pipe, flue gas stack, or propeller nozzle discharges into the atmosphere. It disperses downwind sometimes in a pattern called an exhaust plume.
Smoke is unburned wood particles – you need to improve your technique if you can see smoke from a chimney. Don't burn the garbage in a wood fire. It causes ozone, can damage the inside of your stove and/or flue, and can produce a stain in any food you prepare.
Classic smog – This is the traditional type of smog seen in areas with a humid climate. It's a combination of smoke, fog, and sulfur dioxide. This smog serves as a reducing agent in atmospheric emissions and is thus also known as smog reduction.
So, the correct answer is ‘Photochemical smog’.

Note: Photochemical smog is a mixture of contaminants created as nitrogen oxides and volatile organic compounds (VOCs) respond to sunlight, producing a brown haze over towns. It seems to happen most frequently in the summer since that's when we get the most sunshine.