Question

How does air pollution cause acid rain?

Answer 1

Air pollution can be described as a reduction in the air quality due to the presence of certain harmful gases (chlorofluorocarbons, nitrogen oxides, sulfur dioxide, etc.), particulate matter (dust, fly ash, etc.), etc. This low-quality air is detrimental to all life forms. Man-made causes of this air pollution include large-scale industries waste landfills that generate gas, etc. and the natural causes include volcanic eruptions, forest fires.

Complete answer:
Any form of precipitation, rain or otherwise, that has high acidic content is called acid rain. The two main gases that contribute to this phenomenon are nitrogen oxides and sulfur dioxide. Natural causes such as lightning and volcanic eruptions do generate nitrogen oxides and sulfur dioxide.

However, it is the man-made causes that mainly contribute to the release of these gases in the atmosphere. These include the emissions from the industries especially the coal industry, exhausts of vehicles,

Nitrogen oxides and sulfur dioxide react with components of the air such as water vapour, oxygen, etc. to form sulfuric acid and nitric acids. These gases then precipitate in wet (rain, snow, etc.) or dry form (combined with some particulate matter). The pH range is between $4.2 - 4.4$.

Both nitrogen oxides and sulfur dioxides can easily combine with water vapour and be carried away by the wind to other places. Nitrogen oxides also combine with the volatile organic compounds in the atmosphere to form ground-level ozone. That can easily be carried to other areas by the wind.
People living in regions with ground-level ozone have difficulty breathing, cough, scratchy throat, etc. they may also end up suffering from asthma and bronchitis.

Note: Apart from polluting the air, acid rain also causes water pollution, damage buildings, affect vegetation, and animals especially aquatic animals. The rainwater seeps into the soil and spoils the groundwater along with lakes, ponds, and streams. Some organisms can survive the changes in these water bodies; however, the entire ecosystem does get disturbed because some fail to survive.