Visibility assessment : coping with incomplete emissions and modeling.

The availability of complete emissions and entrainment data, topographic data and statistical meteorology data, and the modeling to account for all aerosol constituents presently found in our atmospheres, is not likely to improve substantially in the foreseeable future. This inability to model all of the transformation and transport processes which result in visibility-impairing aerosol species arriving at a point of interest, does not necessarily prevent our assessment of the benefits of reducing emissions from sources that can be modeled. We must, however, have an adequate statistical record of the concentrations of these materials and we must have a reliable means to apportion the concentration into controllable (i.e., those we can quantify and model) and uncontrollable fractions. Statistical concentration data, for remote scenic regions, are available for relevant aerosol species from the IMPROVE Network, for years beginning in 1988. A comparable network is unfortunately not available for urban areas. Here we describe the evolution of our source apportionment assumptions for two remote sites of much current interest, Grand Canyon and Shenandoah National Parks. Ingenuity and in some cases additional field investigations are necessary to improve such apportionment assumptions. To that end we briefly summarize promising approaches, such as receptor analysis and more » characterization of the particulate loading of on-shore flows, and current DOE research relevant to the issue. « less