5. The Clean Air Act was passed in 1970. To address problems with acid rain, the 1990 Clean Air Act amendments created a nationwide Sulfur Dioxide (SO2) cap-and-trade program, with the goal of cutting SO2 emissions from fossil fuel-fired power plants to one-half of their 1980 levels. SO2 emissions have fallen dramatically since 1980. "SO2 allowances" are traded under the SO2 cap-and-trade program. Chan et al. (2018) found that the allowances were mainly sold by SO2-generating firms located in sparsely populated areas in the western United States and mainly purchased by SO2-generating firms located in densely populated areas in the eastern United States. What concerns does this raise about purely market-based approaches to pollution reduction? Given these concerns, would you suggest putting additional structure on the SO2 cap-trade-program? Why or why not? You do not need a graph for this