Climatology of Aerosol Properties at Mountaintop Sites

摘要

High altitude mountaintop observatories provide the opportunity to make long-term, continuous measurements of aerosol properties in the free troposphere without the added expense and difficulty of operating aircraft. Climatologies of free tropospheric aerosol radiative properties in cloud-free air, including light scattering, light absorption, light extinction, single scattering albedo, 舗gstr鰉 exponent, hemispheric back-scatter fraction and radiative forcing efficiency, from twelve high altitude (2.2-5.1 km) measurement platforms are presented. These climatologies utilize data from ten mountaintop observatories in the 20-50篘 latitude band and two multi-year, aircraft vertical profiling programs. The amount of light absorption and scattering observed from these high altitude platforms either peaks in the spring or has a broad spring to summer enhancement. The seasonal variation and systematic relationships among aerosol properties change from site to site but the timing and links among parameters can be related to aerosol sources known to impact the individual sites. Having first presented an overview of aerosol optical properties for all 12 high altitude sites, we focus on differentiating air masses based on their combined aerosol properties at the three sites in Asia: Pyramid (Nepal), Mount Waliguan (China), and Lulin Mountain (Taiwan), along with Mauna Loa (USA) in the central Pacific. Specifically we use statistical clustering techniques to identify typical air mass trajectories at these four sites and to determine if the resulting clusters can be related to the characteristics of different aerosol types (e.g., dust, smoke). This allows us to determine the contribution of aerosol events to the aerosol climatology at these locations and to propose site-specific rules for identifying aerosol type. Furthermore, these rules could help to constrain both model parameterizations and remote sensing algorithms that are often based on an assumed aerosol type.