NEWS RELEASE NOVEMBER 2014
Particulate Air Pollution Definitions and Goals Keep Changing
For those tasked with making decisions relative to reducing particulate air pollution there is a special challenge. The definitions and the goals keep changing. All these changes are documented in a number of McIlvaine publications and services.
The confusion starts with the very basic definition of particulate. Small particles penetrate the lungs and are of greater concern than large particles. So a definition based on particle diameter (10 microns or 2.5 microns) is used. However, most particles are not spheres. The actual measurement is based on impaction which is a function of size, weight and shape. Needless to say, there is lots of room for confusion and poor decision making based on the definition variables.
Another problem is based on the distinction between total particulate and condensibles. Compounds, which exit the stack as vapors but condense in the atmosphere, are important contributors to pollution. The original power plant air toxic rules limited the total particulate including condensibles but the final version focused just on the discrete fraction.
Measurement methods are a big variable. Stack cleanliness is measured with High Efficiency Particulate Filters (HEPA). However, cleanrooms use HEPA filters for processes and test their efficiency with particle counters. Ambient air is considered clean from a weight perspective, but could contain hundreds of thousands of small particles in every cubic foot.
EPA determined that almost no mercury was discharged as particulate from power plant stacks. So its regulations require only the measurement of gaseous mercury. Unfortunately most of the reduction methods involve converting gaseous mercury to particulate mercury prior to removal. The result is that a plant can report low mercury emissions. but can be discharging the mercury in a particulate form.
McIlvaine tracks all the complexities in a number of publications.
For more information, click on: