What is smog? How is classical smog different from photochemical smog?

Smog is a type of air pollution characterized by a mixture of smoke and fog. It consists of various pollutants, including particulate matter, ground-level ozone, sulfur dioxide (SO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs), among others. Smog can have adverse effects on human health, the environment, and visibility.

There are two primary types of smog: classical smog and photochemical smog, and they differ in their composition and formation:

Classical Smog (London Smog):

Composition: Classical smog is primarily composed of smoke particles (particulate matter) and sulfur dioxide (SO2). It can also contain other pollutants, such as carbon monoxide (CO).
Formation: Classical smog typically occurs in areas where coal or other fossil fuels are burned for heating or industrial processes. It is often associated with cool, humid climates, which is why it is sometimes referred to as "London smog" due to historical occurrences in London.
Chemical Reactions: The formation of classical smog involves the following chemical reactions:
a. Sulfur dioxide (SO2) is emitted from burning fossil fuels.
b. SO2 reacts with moisture in the air to form sulfuric acid (H2SO4), which creates fine aerosol particles.
c. These aerosol particles combine with other pollutants and water droplets to form the characteristic smog.
Photochemical Smog (Los Angeles Smog):

Composition: Photochemical smog is primarily composed of nitrogen oxides (NOx), volatile organic compounds (VOCs), and ground-level ozone (O3).
Formation: Photochemical smog typically occurs in areas with high levels of vehicle emissions and abundant sunlight. It is often associated with warm, sunny climates, such as Los Angeles.
Chemical Reactions: The formation of photochemical smog involves the following chemical reactions:
a. Nitrogen oxides (NOx) and volatile organic compounds (VOCs) are emitted from vehicle exhaust, industrial processes, and other sources.
b. When exposed to sunlight, NOx and VOCs undergo photochemical reactions that produce ground-level ozone (O3) and other reactive compounds.
c. Ground-level ozone is a key component of photochemical smog and can irritate the respiratory system and other health effects.
In summary, classical smog is primarily a product of sulfur dioxide emissions and is associated with cool, humid conditions, while photochemical smog is formed by the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight and is associated with warm, sunny climates. Both types of smog can have harmful effects on human health and the environment, but they have different chemical compositions and formation mechanisms.