Which one of the following is a secondary aerosol?

Secondary aerosols are particles formed in the atmosphere from precursor gases through chemical reactions.

 Key Points

• Sulphate particles are considered as secondary aerosols because they are formed from the oxidation of sulphur dioxide gas (SO2) released by natural and human activities, and the subsequent formation of sulphuric acid.
• The sulphuric acid can condense on pre-existing particles to form new particles, or can combine with other gases to form new particles directly.

Therefore, sulphate particles are formed indirectly from the primary emission of SO2, making them a secondary aerosol.

 Additional Information Black carbon contributes to climate warming, mineral particles affect atmospheric chemistry, and sea salt has a role in cloud formation and precipitation.