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U.S. DEPARTMENT OF THE INTERIOR 



NATIONAL PARK SERVICE 



Briefing Statement 



April 28. 1994 



REGION/OFFICE : WASO, Air Quality Division, Research Branch 



ISSUE : Air Quality - Determination of Sources of Pollutants 



BACKGROUND : To track progress on "remedying existing and preventing future impairment of 

 visibility" in national parks, the NPS must determine which pollutants contribute to impairment, 

 identify the sources or source areas which emit them, and then understand the transport 

 mechanisms which bring them into the parks. 



The NPS has conducted research on methodologies for identifying source areas since 1978. There 

 are two basic methods which can be used to estimate the impact of a source on a park. These are 

 1) modeling forward from the source or 2) modeling backward from the park (receptor). Because 

 emission information is often unavailable or highly uncertain, NPS has performed "receptor 

 modeling" in which data obtained at a park is used to back calculate where the pollutants were likely 

 to have arrived from. The data necessary for receptor modeling are obtained by monitoring the 

 pollutant concentrations in the parks while the necessary meteorological data are usually obtained 

 from the National Climatic Data Center. Intensive field studies occasionally provide additional 

 data. 



CURRENT STATUS : Several receptor modeling techniques have been developed and employed 

 by the NPS. Results of these models show clearly that pollutants which impair visibility in many 

 NPS units often originate hundreds of miles from the parks and frequently cross state and 

 international boundaries during transport from the sources to the receptors. Several examples are 

 shown in Figures 1 through 5. The graphs show where air masses are most likely to arrive from on 

 days when the particulate sulfate concentration at the park is high. The plotted values are relative 

 probabilities. For example, a value of 3 means that air was 3 times as likely to arrive from that area 

 as would be expected by random events alone. Each graph is based on 7-11 years of data. 



Sources in Mexico are the largest contributors to high sulfate concentrations in the Southwestern 

 United States. Figures 1 through 3 show examples of high sulfate source regions for, Big Bend and 

 Guadalupe Mountains National Parks in Texas, and Chiricahua National Monument in Arizona. 

 Most sulfate at Big Bend and Guadalupe Mountains originates in Mexico with the highly 

 industrialized Monterrey, Mexico, area being a large contributor. High sulfate days at Chiricahua 

 are associated with air masses arriving from the copper smelter region of both Arizona and Mexico 

 as well as the entire border region between the southwestern states and Mexico. Because Mexico 

 is a significant and possibly the primary contributor to sulfate in the Southwest the effectiveness of 

 any control strategy implemented by the United States will be partially offset by emissions from 

 Mexico. 



Results for Glacier National Park in Montana and Acadia National Park in Maine, shown in Figures 

 4 and 5, clearly show that sources in Canada contribute significantly to sulfate loading in these 

 parks. High sulfate days at Glacier are often associated with transport of air masses from the front 

 range of the Canadian Rockies including the Edmonton, Alberta area where there are oil refining 

 and other fossil fuel related activities. High sulfate concentrations at Acadia are often associated 



