ACES


The measurements used in this study were taken as part of the Ad-Hoc Ceilometer Evaluation Study (ACES); a collaboration between the U.S. EPA Office of Research and Development and the University of Maryland, Baltimore County (UMBC), to help guide the implementation of hourly mixing layer heights (MLH) for the U.S. EPA’s PAMS. Because the hourly MLH requirement requirement is not limited to a particular profiling system, ACES was an independent study to evaluate available commercial ceilometers as the mostly likely instrumentation to be used in PAMS. ACES goals included the evaluation of the attenuated backscatter from commercially available ceilometers, the commercial software and firmware, the assessment of the daytime MLH determination with a focus on transition periods (i.e., morning mixing layer growth and afternoon mixing layer decay), and the development of a unified PBL retrieval method using aerosol backscatter signals. Four commercial ceilometers (Lufft CHM15k, Vaisala CL51, Vaisala CL31, and Campbell SkyVUE PRO) were collocated at the UMBC in Catonsville, Maryland (39.25448N, 76.70958W), between 1 and 15 December 2016. The campaign was focused on the winter months because this would display the most challenging conditions for Planetary Boundary Layer height retrievals as cooler surface temperatures, reduced daylight hours, and minimum solar radiation lead to stable and stratified Planetary Boundary Layer conditions in addition to relatively lower aerosol content during winter periods (Caicedo et al., 2020).



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