The United States has seen large improvements in air quality over the last half century with the implementation of regulations designed to reduce air pollutant emissions. Regulatory costs, estimated by the Environmental Protection Agency at tens of billions of dollars per year, motivate air pollution accountability research, which evaluates impacts of air quality regulations on emissions, air quality, exposure/dose, and public health— components of the so-called Accountability Chain. This work adds to the expanding air pollution accountability field by investigating a range of regulatory actions on electricity generating units and on-road mobile sources promulgated since the 1990s. Results show that the United States has seen major emissions reductions over this period, and most of the decreases are attributable to regulatory policies, although influences such as fuel costs, demographic shifts, and technological improvements have influenced emissions reductions as well.
The bulk of this work investigates the impacts of changing emissions on air quality in the Eastern United States. Analyses focus on ambient ozone and particulate matter with diameter less than 2.5 μm (PM2.5), two pollutants linked with adverse health and environmental impacts. Observation-based statistical models and a deterministic air quality model (the Community Multiscale Air Quality model—CMAQ) show that emissions reduction programs reduced the highest ozone concentrations while simultaneously increasing the lowest concentrations. For PM2.5, controls reduced both the annual mean values and the variability. Meteorology had large impacts on daily pollutant concentrations, but long-term trends were driven by emissions reductions. An evaluation shows that CMAQ captured ozone and PM2.5 concentrations and changes over the decade, but the model did not always get the right answer for the right reasons. For example, the model had trouble estimating absolute concentrations and variability of certain species that make up PM2.5, but the biases canceled out when the species were summed.
This research provides important evidence that links regulations to emissions reductions and air quality improvements while accounting for numerous concurrent changes. Lessons learned in accountability research can be applied to future air quality management strategies, and this work provides two examples: one using empirical and CMAQ modeling of ozone in the United States, and another using an integrated assessment of energy, air pollution, and climate policies in South Africa.
Dr. Armistead G. Russell
Dr. James A. Mulholland, Dr. Patricia L. Mokhtarian, Dr. Athanasios Nenes (EAS), Dr. Paige E. Tolbert (Emory University)