8.5.4 Challenges in Developing and Using ISM Data

Regulatory agencies are most accustomed to working with discrete sample data sets, with a variety of concentration measurements from within an area of interest. It is not surprising that some regulatory criteria are written specifically to deal with these data sets, specifying decisions to be made based upon data parameters readily obtained (e.g., mean, maximum concentration observed). ISM data, while providing in most cases a better estimate of the mean, cannot provide all of the parameters that may be called for in some regulations (e.g., maximum concentration observed, upper percentile concentrations observed). This shortcoming can constitute a regulatory barrier to acceptance, as noted in some of the sections below. Other sections address other practical problems associated with the nature of ISM and discrete data that may limit regulatory acceptance of ISM.