What international agreement aimed to reduce air pollution between Canada and the US?

The Air Quality Agreement is the correct choice as it specifically addresses air pollution issues between Canada and the United States. This agreement was established in 1991 and aims to collaboratively manage and reduce transboundary air pollutants, particularly sulfur dioxide (SO2) and nitrogen oxides (NOx). These pollutants can lead to acid rain, which poses significant environmental and health risks. By setting specific targets and cooperative measures, the Air Quality Agreement effectively promotes coordinated efforts to improve air quality in both countries.

In contrast, the Montreal Protocol focuses on phasing out substances that deplete the ozone layer, while the Copenhagen Accord and the Kyoto Protocol are broader international agreements aimed at combating climate change and reducing greenhouse gas emissions, rather than specifically targeting air pollution between Canada and the U.S.