Sulfur Oxides (SOX) and Nitrogen Oxides (NOX) are the major emissions that caused acid rain. 3 things happen to mitigate this :
1> The tough environment laws in the US, made many chemical companies to move out of the US and setup shop in other countries, thereby taking production and jobs with them.
2> SOx (sulfur oxides) was solved over time by using alkaline components like lime to coal in coal power plants. Refineries made ultra low sulfur diesel and generally sulfur in all fuels were reduced.
It is important to note that although SOx makes acid rain, it is a “global cooling” gas (opposite of CO2 which is causing “global warming”)
3> NOX (Nitrogen Oxides) was solved by redesigning burners, using ammonia, and using catalytic reduction of NOX (like the catalytic converters in cars).