Question

Read the following statements regarding the PAN (peroxyacyl nitrates) and select the correct ones.
(i) It is a secondary pollutant present in photochemical smog.
(ii) It is produced by photochemical reactions between hydrocarbons and nitrogen oxides in the presence of sunlight of UV radiations.
(iii) It is thermally unstable and decomposes into peroxyethanoyl radicals and nitrogen dioxide gas.
(iv) It is a lachrymatory substance, causing irritation of eyes.

• A. (i) and (ii)`
• B. (iii) and (iv)
• C. (i), (ii), and (iii)
• D. (i), (ii), (iii) and (iv)

Answer 1

Answer: (D)

(i), (ii), (iii) and (iv)

Secondary pollutants are pollutants which form in the atmosphere. These pollutants are not emitted directly from a source (like vehicles or power plants). Instead, they form as a result of the pollutants emitted from these sources reacting with molecules in the atmosphere. Secondary pollutants are concerning as they can be formed from many different compounds. Photochemical smog is made up of various secondary pollutants like ozone, peroxyacyl nitrates (PANs), and nitric acid.

A hazy condition of the atmosphere caused by the reaction of hydrocarbons with molecules of nitrogen oxide in sunlight, which produces complex organic molecules of peroxyacetyl nitrates (PAN). In humid conditions these molecules produce smog. Such phenomena are common in large urban areas (e.g. the Los Angeles basin and Athens) where there are stable atmospheric conditions and a high level of hydrocarbon input from incomplete combustion in car engines. Natural photochemical reactions occur in the high atmosphere with the absorption of radiation by oxygen to produce ozone.

Peroxyacetyl nitrate (PAN; CH3C(O)OONO2) is an important constituent of photochemical smog. It is also a ubiquitous chemical present throughout the global troposphere. PAN is thermally unstable, however, and decomposes at higher temperatures to reform peroxyacetyl radicals and NO2, that is, the reverse of reaction.

Peroxyacyl nitrates (also known as Acyl peroxy nitrates, APN or PANs) are powerful respiratory and eye irritants present in photochemical smog. They are lachrymators, causing eye irritation at concentrations of only a few parts per billion. At higher concentrations they cause extensive damage to vegetation.

So the correct option is '(i), (ii), (iii) and (iv)'.