Three questions with Kyung-Min Nam

How do pollution and carbon emissions control interact?

Carbon dioxide (CO₂) and conventional pollutants like sulfur dioxide (SO₂) and nitrogen oxides (NO_x) are often byproducts of the same activities, such as fossil fuel combustion. Accordingly, regulating pollution resulting from these activities affects carbon emissions, and regulating carbon emissions affects pollution. We studied the effects of abating pollution on carbon emissions, and the effects of mitigating carbon emissions on pollution. We analyzed these relationships in both China and the U.S. to compare the effects of the different emissions trends and energy mixes in each country.

Why study this relation in two directions, and in two different countries?

There are two primary motivations. One is the need for more attention to the potential ancillary carbon-mitigation benefits associated with pollution control. Given the difficulty reaching international agreement on CO₂, reducing carbon emissions through pollution regulations may be more realistic. In fact, countries tend to be more apt to undertake efforts to control conventional pollutants than carbon emissions, as costs of excess pollution or the benefits of reduced pollution are felt more directly in the country undertaking control. However, the focus of existing literature leans toward ancillary air quality benefits resulting from carbon reductions, giving little attention to non-target effects in the reverse direction, which we also focus on in this study.

The other motivation is to compare the relative magnitude of the effects of pollution-carbon control in the two countries. Instead of the monetary measures conventionally used, we estimate the ratio of the change in the untargeted gases to the change in the gases targeted by regulations-a measure that can be readily compared across countries. 

What did you find? 

In both countries, ancillary carbon reductions resulting from SO₂ and NO_x control tend to rise with the increased stringency of pollution control targets, reflecting the eventual need for wholesale change toward non-fossil technologies when large reductions are required. Under stringent pollution targets, the non-target effects tend to be substantially higher in China than in the U.S., due to China's heavy reliance on coal. These results are promising in that China's efforts to reduce local air pollution will result in substantial global carbon reductions. We also find that in both countries substantial ancillary SO₂ and NO_x reductions can be attained through carbon control. However, unintended effects in this direction depend less on the stringency of control and are stronger in the U.S. than in China. A key implication of our results is that future pollution and carbon mitigation targets need to consider synergistic effects to improve coordination and reduce unnecessary policy compliance costs.