- Student Dissertation or Thesis
Recent scientific assessments reveal interactions between global climate change and urban air pollution and imply that opportunities exist to simultaneously deal with these two issues from a policy perspective. This thesis addresses one side of the topic: the air-quality co-benefits of a climate policy, focusing on the regional, temporal, and specie-specific responses. From a policy perspective, it is crucial to understand these responses in order to set a sound framework for climate policy with co-benefits.
This thesis research establishes the links between a newly developed detailed model of urban-scale chemical and physical processing (Metamodel) and the Massachusetts Institute of Technology (MIT) Integrated Global Systems Model (IGSM). These linkages will ultimately enable the sub-components of the IGSM, including the new Metamodel, to communicate interactively. As a first step, the study conducts a preliminary analysis by running the Metamodel in offline mode by providing the actual dataset from the IGSM to the Metamodel exogenously. The study uses two scenarios: the "CO2 stabilization policy" (450ppm policy) and the "no policy" cases and compares the impacts of the 450ppm policy for the period from 2001 through 2100 on the key air pollutants: O3, CO, NO2, SO2, HCHO, sulfate aerosols, black carbon, organic carbon, and nitrate aerosols.
The findings of the study are 1) the 450ppm policy will likely reduce key air pollutants except O3; 2) the variability of the impacts by species is significant — the magnitude of the reductions would be largest for SO2, more than -10%, followed by organic carbon, nitrate aerosols, HCHO, sulfate aerosols, and black carbon, between -10% to -5%, though CO and NO2 would be much less affected, less than -5%; 3) for the affected species except SO2 and sulfate aerosols, the impacts become larger as time advances; 4) the magnitude of the impacts vary widely by region due to not only the reduction of emissions but also meteorological conditions; and 5) the variability of the results for sulfate aerosols, BC, OC, and nitrate aerosols may be highly uncertain compared to other species, taking into account the large statistical uncertainties of the monthly mean concentrations.
The thesis also explains other methodological challenges for assessing the air-quality co-benefits. Furthermore, the thesis examines barriers to implementation of the air-quality co-benefits in practice and, finally, provides implications for future policy design based on the above findings.