What mechanism explains how distant emissions can cause acid deposition in downwind regions?

• A. Long-range transport via atmospheric currents.
• B. Photochemical smog only.
• C. Local emissions only.
• D. Deposition only from sea spray.

Answer: (A)

Distant emissions cause acid deposition far away because pollutants like sulfur dioxide and nitrogen oxides can be carried by atmospheric currents over long distances. While in the air, these gases oxidize and react with water and other chemicals to form sulfuric and nitric acids, often attaching to particles as sulfate and nitrate aerosols. These acidic compounds are then deposited on the surface either through precipitation (wet deposition) or by direct settling (dry deposition), delivering acidity to distant soils and bodies of water. This long-range transport contrasts with local, near-source effects and with other phenomena like photochemical smog or sea-spray deposition, which are not the primary mechanisms for downwind acid deposition.