Question

Which photochemical oxidants are formed by the action of sunlight on nitrogen oxides and reactive hydrocarbons?

• A. peroxyacetyl nitrate
• B. acid rain
• C. inorganic carbon
• D. particulate matter

Hint:

• Photochemical smog forms when sunlight acts on nitrogen oxides (NO$_x$) and volatile organic compounds (VOCs/reactive hydrocarbons).
• This produces secondary pollutants called photochemical oxidants.
• Key photochemical oxidants include ground-level ozone (O$_3$) and peroxyacetyl nitrate (PAN).
• PAN is known for causing eye irritation and damaging plants.

Answer 1

The Correct Option is A

Photochemical smog is a type of air pollution produced when sunlight reacts with nitrogen oxides (NO$_x$) and volatile organic compounds (VOCs), which include reactive hydrocarbons. This complex series of reactions leads to the formation of various secondary pollutants, known as photochemical oxidants. Key photochemical oxidants include:

• Ozone (O$_3$): Ground-level ozone is a major component of photochemical smog and a strong oxidant.
• Peroxyacetyl Nitrate (PAN): PAN (CH$_3$COOONO$_2$) is another significant photochemical oxidant. It is a lachrymator (causes eye irritation) and is phytotoxic (harmful to plants). It is formed from the reaction of peroxyacetyl radicals with nitrogen dioxide (NO$_2$).
• Aldehydes (e.g., formaldehyde, acetaldehyde) and other peroxyacyl nitrates.

Option (a) peroxyacetyl nitrate (PAN) is a well-known photochemical oxidant formed under these conditions. Option (b) acid rain is primarily formed from sulfur dioxide and nitrogen oxides reacting with water, but it's not typically classified as a photochemical oxidant in the same way as ozone or PAN. While NO$_x$ is involved, the term "photochemical oxidants" usually refers to O$_3$, PAN, etc. Option (c) inorganic carbon (e.g., CO$_2$) is not a photochemical oxidant. Option (d) particulate matter can be primary (emitted directly) or secondary (formed in the atmosphere). Some secondary particulate matter can be formed during photochemical reactions, but PAN is a specific gaseous photochemical oxidant. Given the options, peroxyacetyl nitrate is a classic example of a photochemical oxidant formed from NO$_x$ and hydrocarbons in the presence of sunlight. \[ \boxed{\text{peroxyacetyl nitrate}} \]