The burning of fossil fuels also produces nitrous oxides and sulfur dioxides
These dissolve in water vapour in the atmosphere and react with water to form acids
This water vapour condenses into clouds and will then fall as acid rain

Oxides of nitrogen + water → Nitric acid

Sulfur dioxide + Water → Sulfuric acid

The high temperature inside an internal combustion engine allows nitrogen from the air to react with oxygen to make oxides of nitrogen. These gases irritate the lungs and cause acid rain.

Catalytic converters remove carbon monoxide from exhaust fumes according to the following equation:
2CO+2NO→N2+2CO2 2CO + 2NO \rightarrow N_2 + 2CO_2