95 



Ohio Valley and the Upper Midwest), and that the magnitude of airflow from this direction 

 had increased from 1948 through 1970; since then the amount of northwesterly flow had 

 declined somewhat. 



This observation has never been factored into calculations on the impact of legislation on 

 visibility in Shenandoah or other Parks or Class 1 areas. However, it is clear that it would 

 have some effect of increasing the apparent reduction in visibility through 1970 and then 

 providing some improvement thereafter. 



REGULATORY IMPLICATIONS 



If it is the perception of declining visibility in Shenandoah Park that serves as the basis for 

 regulatory policy, that perception is incorrect. There has been no net decline in the last 

 quarter-century; there in fact have been some statistically significant improvements since 

 then. 



In addition, the Clean Air Act Amendments of 1990, particularly those with respect to 

 sulfur dioxide emissions, have yet to take effect. If the primary cause of temporal change 

 Shenandoah regional visibility trends is from this source, then visibility will improve (if not 

 compensated for by natural weather variability). The next five years will therefore certainly 

 provide an important test of our understanding of the causes of visibility changes in this 

 area. 



The data that form my testimony consist of 950,000 separate observations of visibility 

 taken by over 100 professionally trained observers since 1959. When then was a decline- 

 which occurred in July and August only, and ended in 1970 and 1973, respectively-the 

 decline was simultaneously noted at all the airports surrounding Shenandoah. The 

 correlation between all of the airport data is highly significant, and the Park lies squarely 

 between all of these sites. It is obvious that the trends in this data are a better representative 

 than any other source of the true trends in visibility in the Shenandoah Park. 



While there have been changes in emissions upstream from the Park, there have also been 

 simultaneous and significant changes in climate. These changes would serve to amplify the 

 changes in visibility observed in the long term record. However, they have not been 

 factored into the regulatory process to date. 



It is important that regulation be based upon sound science; perhaps nowhere is this more 

 imperative than in Environmental Science. If a perceived reduction in visibility since the 

 first Clean Air Act in the Shenandoah and surrounding rural areas is the cornerstone of new 

 regulation with respect to those areas, such regulation will not be based upon the most 

 exhaustive survey of trained-observer visibility data ever conducted over these areas. 



