Acidic Deposition and Material Effects: Critical Evaluation of NAPAP Assessment

Abstract

The 79th APCA Annual Meeting in Minneapolis featured a technical session on materials damage from acid deposition. The central theme of this session was the materials damage assessment methodology being developed by the National Acid Precipitation Assessment Program (NAPAP). Eight papers were presented in this session: one describing recommended general procedures for the derivation of damage functions (one of the critical elements of this assessment methodology) and three describing various specific elements of the NAPAP methodology. These include descriptions of some of the methods used (a) to define the quantities of materials exposed to acid deposition, (b) to characterize the exposure, and (c) to estimate the economic damage. The latter paper also includes estimates of damage. The remaining four papers criticize various aspects of the NAPAP assessment and outline some recommendations for improvements. Edited summaries of each of the papers, prepared by the various authors, are presented here, followed by the chairman’s summary of the session as a whole.

The NAPAP assessment methodology is based on the damage function method, a “bottom-up” technique in which economic losses due to materials degradation are estimated by computing the sum of the products of the amount of various types of materials at risk (the materials inventory) times the unit replacement or maintenance costs, times the incremental frequencies of such replacement or maintenance actions attributable to acid deposition. The incremental frequencies are derived from damage functions (for which the arguments are various air quality or deposition parameters) and the allowable or critical loss, exceedance of which is assumed to trigger such maintenance actions. This information is then summed over some geographic area. In the first NAPAP application of this methodology,1 this summation was performed over 117 Metropolitan Statistical Areas in 17 northeastern states.

It should be emphasized that NAPAP has not endorsed the findings of this assessment, primarily because of reservations about the substantial uncertainties in some of its component parts. Nevertheless, some of the results have appeared in various symposia proceedings^2-4 and the basic methodology remains in place, awaiting better input information from the NAPAP research program. Thus review and criticism of the features and limitations of this approach is timely and useful.