<p>The IMPROVE sampler is opened in order that filters may be changed.</p>
<p>Since 1982, Shenandoah National Park scientists have been collecting particulate matter as part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network. This program is being implemented at sites around the country to better understand how air pollution affects what we can see.
The four white boxes at the sampling station are known as samplers and each one contains a pump that draws in air from a tube that extends above the shelter. Each of the samplers has specialized filters that capture different types of particles from the air drawn in through the tube. Park staff (like Liz!) collect these filters every week and mail them to a laboratory for analysis. 
Scientists examine the filters and identify how many and what kinds of particles are in the air and figure out how much the pollutants affect visibility and where they likely came from. . From this work, we know that pollution at Shenandoah National Park arrives from local, regional, and even international sources.</p>
Mary O'Neill
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