Question

Photochemical smog was first observed in-
A. Los Angeles
B. Tokyo
C. New York
D. Sydney

Answer 1

Photochemical smog is a mixture of pollutants. This is caused when nitrogen oxides and volatile organic compounds react with the ultraviolet rays of the sunlight. This causes a brown haze and is mostly observed during morning and afternoon. Thus it is abundant in the cities where temperature is relatively higher. This was first observed in $1940$.

Complete answer-
Option A Los Angeles- the photochemical smog was first spotted in Los Angeles in $1940$.
Option A is the correct answer.
Option B Tokyo- Tokyo city also got troubled by air pollution but it was not the city to report it first.
Hence option B is not the correct answer.
Option C New York- New York reported a smog episode in the year $1966$ where the city was filled with damaging levels of toxic pollutants.
Option C is not the correct answer.
Option D Sydney- Sydney air pollution is under control as work under bush fire season and wood smoke was high in $2020$.
Option D is not the correct answer.

Therefore, Option A is the correct answer.

Note:
This is mostly observed during summer. The largest contributor for this harmful effect is the automobiles, the coal-fired plants and other power plants. This was first observed in Los Angeles in $1940$ in the summer. This was formed because the mixture of nitrogen oxide and hydrocarbons reacted to the ultraviolet rays present in the sunlight. The effect of this is harmful for all animals including humans as these can damage our respiratory system.