Particulate Matter Assessment Focuses on Urban Visibility
EPRI recently submitted comments to the U.S. Environmental Protection Agency (EPA) on the External Review Draft of the Particulate Matter Urban-Focused Visibility Assessment.  The assessment focuses on the effectiveness of a one-hour peak light extinction–based indicator for a possible secondary PM National Ambient Air Quality Standard based on visibility in urban areas.  A primary concern expressed by EPRI was that the diurnal PM component profiles used to get hourly concentrations of PM species from the 24-hour measurements are based on the Community Multiscale Air Quality (CMAQ) model.  The hourly component concentrations are needed as input to the IMPROVE light extinction equation to get hourly values of light extinction to determine possible nonattainment.  The CMAQ model has not been validated for this application, and it is known to have substantial inaccuracies in estimating diurnal profiles of many PM components.  Another comment noted the lack of justification for using the current IMPROVE equation—developed for regional haze in remote areas—for haze in urban areas.  For more information, contact Naresh Kumar, (650) 855-8758, nkumar@epri.com or Stephanie Shaw, (650) 855-2353, sshaw@epri.com.