Peter Percell

Note on a global homotopy

In a lecture given at the M.R.C. Symposiucn on Recent Advances in Numerical Analysis in May, 1978, H. B. Keller discussed a global homotopy method for finding solutions of f (u) = 0. At that time he was unable to show that one of the hypotheses of his main result is satisfied by almost all initial points for paths determined by his method. The purpose of this note is to fill that gap in Kellers result.

Differences Between Magnitudes and Health Impacts of BC Emissions Across the United States Using 12 km Scale Seasonal Source Apportionment

Recent assessments have analyzed the health impacts of PM2.5 from emissions from different locations and sectors using simplified or reduced-form air quality models. Here we present an alternative approach using the adjoint of the Community Multiscale Air Quality (CMAQ) model, which provides source-receptor relationships at highly resolved sectoral, spatial, and temporal scales. While damage resulting from anthropogenic emissions of BC is strongly correlated with population and premature death, we found little correlation between damage and emission magnitude, suggesting that controls on the largest emissions may not be the most efficient means of reducing damage resulting from anthropogenic BC emissions. Rather, the best proxy for locations with damaging BC emissions is locations where premature deaths occur. Onroad diesel and nonroad vehicle emissions are the largest contributors to premature deaths attributed to exposure to BC, while onroad gasoline emissions cause the highest deaths per amount emitted. Emissions in fall and winter contribute to more premature deaths (and more per amount emitted) than emissions in spring and summer. Overall, these results show the value of the high-resolution source attribution for determining the locations, seasons, and sectors for which BC emission controls have the most effective health benefits.

Premature deaths attributed to source-specific BC emissions in six urban US regions

Recent studies have shown that exposure to particulate black carbon (BC) has significant adverse health effects and may be more detrimental to human health than exposure to PM2.5 as a whole. Mobile source BC emission controls, mostly on diesel-burning vehicles, have successfully decreased mobile source BC emissions to less than half of what they were 30 years ago. Quantification of the benefits of previous emissions controls conveys the value of these regulatory actions and provides a method by which future control alternatives could be evaluated. In this study we use the adjoint of the Community Multiscale Air Quality (CMAQ) model to estimate highly-resolved spatial distributions of benefits related to emission reductions for six urban regions within the continental US. Emissions from outside each of the six chosen regions account for between 7% and 27% of the premature deaths attributed to exposure to BC within the region. While we estimate that nonroad mobile and onroad diesel emissions account for the largest number of premature deaths attributable to exposure to BC, onroad gasoline is shown to have more than double the benefit per unit emission relative to that of nonroad mobile and onroad diesel. Within the region encompassing New York City and Philadelphia, reductions in emissions from large industrial combustion sources that are not classified as EGUs (i.e., non-EGU) are estimated to have up to triple the benefits per unit emission relative to reductions to onroad diesel sectors, and provide similar benefits per unit emission to that of onroad gasoline emissions in the region. While onroad mobile emissions have been decreasing in the past 30 years and a majority of vehicle emission controls that regulate PM focus on diesel emissions, our analysis shows the most efficient target for stricter controls is actually onroad gasoline emissions.

Application of static adaptive grid techniques for regional-urban multiscale air quality modeling

Texas Air Quality Study 2000 revealed that ozone productivity in the Houston Ship Channel area was abnormally higher than other comparable cities in USA due to the large emissions of highly reactive unsaturated hydrocarbons from petrochemical industries. Simulations with popular Eulerian air quality models were shown to be inadequate to represent the transient high ozone events in the Houston Ship Channel area. In this study, we apply a multiscale Eulerian modeling approach, called CMAQ/SAFE, to reproduce the measured ozone productivity in the Houston Ship Channel and surrounding urban and rural areas. The modeling tool provides a paradigm for the multiple-level regional and local air quality forecasting operations that can utilize modern computational infrastructure such as grid computing technologies allowing to harness computing resources across sites by providing programmatic and high-bandwidth data linkage and establishing operational redundancy in the case of hardware or software failures at one operational site.