Commentary challenging the conclusions offered in the article by Carl Abbott in this issue.

This article offers a comprehensive overview of the diverse and expansive cultural resources managed by the U.S. National Park Service (NPS), emphasizing the growing significance of historical and archaeological preservation within the system. Holland highlights the evolution of the NPS's attitudes and practices, moving from a primarily natural-resource-focused approach to a more sophisticated understanding and stewardship of cultural heritage. The article details the scope of resources under NPS care—including thousands of historic structures, archaeological sites, and museum objects—and addresses both achievements and ongoing challenges, such as inadequate data collection, deferred maintenance, and funding limitations. Case studies, including Golden Gate National Recreation Area and Lowell National Historical Park, illustrate innovative management models and adaptive reuse strategies. Holland also discusses the implications of external pressures, such as urban encroachment and energy development, and advocates for increased collaboration, funding diversification, and preservation advocacy to ensure the sustainability of the nation's cultural assets.

Ground-based measurements of aerosol and trace gases were conducted at a rural site in Beijing in the summer of 2006 as a part of the Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing 2006). The size-resolved chemical composition of submicron aerosol was measured using an Aerodyne quadrupole aerosol mass spectrometer (AMS). The data obtained from 15 August to 10 September 2006 are presented. Meteorological analysis shows that the measurement period can be characterized as a cycle of low wind speed periods over the course of a few days (stagnant periods) followed by rapid advection of clean air from the north/northwest mostly due to passage of a midlatitude cyclone. Mass concentrations of total measured aerosol with diameters less than 1 μm. (total. PM1), which is defined as the sum of elemental carbon and nonrefractory components measured by the AMS, were highly variable, ranging from. ∼2 to ∼100 μm-3, Large variability of the PM1 composition and drastic changes in the sulfate (SO 2-4) size distribution were observed to be associated with the cycle of stagnant periods and advection of clean air, indicating that both chemical and physical properties of aerosols were significantly altered on a time scale of a few days. We have found the dominance of organic aerosol at lower total PM1 mass loadings and that of SO2-4 at higher mass loadings, which may have important implications for the PM control strategy in Beijing. Possible factors affecting the evolution of the mass concentration and size distribution of SO2-4 are discussed. Copyright 2009 by the American Geophysical Union.