# Identify the secondary pollutant among the following

$\begin{array}{1 1}(a)\;CH_4&(b)\;\text{Peroxy acetyl nitrate}\\(c)\;SO_2&(d)\;NO\end{array}$

Toolbox:
• A primary pollutant is an air pollutant emitted directly from a source.
• A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.
• Examples of a secondary pollutant include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides ($NO_x$) combine in the presence of sunlight; $NO_2$, which is formed as NO combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water.
Peroxy acetyl nitrate.
Hence (b) is the correct option.
edited Apr 2, 2014