Acid rain (acid deposition) forms when water vapour in the air interacts with nitrogen oxides (NOx) and suphur dioxide (SO2), emitted by industries and vehicles burning fossil fuels (oil, coal and gas). This interaction forms sulphuric acid and nitric acid, which fall to the ground as precipitation: dew, drizzle, fog, snow or rain. Acid rain can travel long distances, with winds carrying them thousands of miles.
While acid rain is in the air, its constituents can endanger human health and decrease visibility. These constituents are nitrogen oxides, sulphur dioxide, and particulate matter (PM) in the form of sulphates and nitrates. Once it has reached ground level, acid rain acidifies lakes and streams that don't have the natural alkalinity needed to neutralize the acid, which can harm or kill plant and animal life. Acid rain damages trees and sensitive forest soils. It also speeds up the decay of buildings and paints, including valuable, historic buildings and statues.
Acid rain is a problem in eastern Canada because many of the water and soil systems aren't alkaline, and therefore cannot neutralize the acid. Here in the west, most of British Columbia has not been affected by acid rain, due to resistant soils that can neutralize acid, and easterly winds. Another factor is B.C.'s lower level of industrialization and, therefore, the emissions that cause acid rain.
A cautionary note, though: Some lakes and soils in B.C. are similar to those in eastern Canada, with low alkalinity, so they're vulnerable to acid rain. If industrial and transportation emissions containing sulphur dioxide and nitrogen oxide increase, those parts of B.C. could be affected, just as eastern Canada is.
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