Acid deposition, often known as acid rain, is an example of a "transfrontier" pollution. It means that the pollution doesn't stay where it is produced but travels across borders, affecting regions even far away from the source. Imagine a big cloud of pollution leaving one country and then raining down on another. Bummer, isn't it?

The two troublemakers that cause acid rain are sulfur dioxide (SO2) and nitrogen dioxide (NO2). Major culprits? Coal-fired power stations and areas with heavy traffic. These places blast out these chemicals into the atmosphere like party poppers, except it's not a party for anyone.

Where does this acid rain often land? Some major targets include places downwind of industrial regions. Imagine you're standing in Scandinavia, you'd see that you're downwind from Western Europe's industrial belts. Similarly, north-east USA and eastern Canada get hit by acid deposition from the US industrial belt.

Scandinavia has seen less acidification recently, not because the wind got tired, but because Western Europe now has less heavy industry. This means fewer pollutants are produced, resulting in less acid rain. It's like less confetti from the party poppers.