Science Inventory

An automated common algorithm for planetary boundary layer retrievals using aerosol lidars in support of the U.S. EPA Photochemical Monitoring Assessment Program

Citation:

Szykman, J., D. Williams, V. Caicedo, R. Delgado, T. Knepp, K. Cavender, AND B. Lefer. An automated common algorithm for planetary boundary layer retrievals using aerosol lidars in support of the U.S. EPA Photochemical Monitoring Assessment Program. Journal of Atmospheric and Oceanic Technology. American Meteorological Society, Boston, MA, , 1-51, (2020). https://doi.org/10.1175/JTECH-D-20-0050.1

Impact/Purpose:

The PAMS monitoring regulations require states to measure hourly mixing height (MH) at required PAMS sites by October 2021. The primary objective of this requirement is to improve the paucity of MH measruements by providing hourly MH for the routine evaluation of chemical transport models such as WRF-CMAQ. OAR-OAQPS expects most states to meet this requirement through use of a ceilometer. Over the past several years CEMM has evaluated commercially available ceilometers and the proprietary software provided by vendors for calculating MH. Currently no standard methodology exists that can be used across different commercially available ceilometers for MH. Under this research, we will develop, test, and implement a common algorithm for calculating continuous MHs from commercially available ceilometers, and other available profiling instruments such as wind lidars. This manuscript present the result of a common algorithm which can be implemented in support of the PAMS program. The second part of this effort will include the development of a prototype data archive system for the raw profile backscatter data and use of this common MLH processing algorithm that will serve as consistent, traceable alternative for state and local agencies to use in place of vendor-supplied proprietary software. The prototype data archive system is currently under developed in collaboration with Maryland Department of the Environment, University of Maryland Baltimore County, and NASA, with the goal of the archive being hosted at one of NASA's National Data Centers. An initial functioning prototype will be demonstrated by early FY21 in conjunction with several volunteer states in the OTR. This effort will also explore additional uses of ceilometer data, including the detection of aerosol layers in the troposphere associated with smoke-transport and evaluation of satellite retrievals algorithms from instruments such as TROPOMI, with a goal of maximizing use of ceilometer backscatter profile data in support of other EPA applications, such as exceptional event analysis.

Description:

A unique automated planetary boundary layer (PBL) retrieval algorithm is proposed as a common cross-platform method for use with commercially available ceilometers for potential implementation under the U.S. Environmental Protection Agency Photochemical Assessment Monitoring Stations program. This algorithm addresses instrument signal quality and screens for precipitation and cloud layers before the implementation of the retrieval methodology using the Haar wavelet covariance transform method. Layer attribution for the PBL height is supported with the use of continuation and time-tracking parameters, and uncertainties are calculated for individual PBL height retrievals. Commercial ceilometer retrievals are tested against radiosonde PBL height and cloud-base height during morning and late afternoon transition times, critical to air quality model prediction and where retrieval algorithms struggle to identify PBL heights. A total of 58 radiosonde profiles were used and retrievals for nocturnal stable layers, residual layers and mixing layers were assessed. Overall good agreement was found for all comparisons with one system showing limitations for the cases of nighttime surface stable layers and daytime mixing layer. It is recommended that nighttime shallow stable layer retrievals be performed with a recommended minimum height or with additional verification. Retrievals of residual layer heights and mixing layer comparisons revealed overall good correlations to radiosonde heights (correlation coefficients, r2, ranging from 0.89 - 0.96 and bias ranging from ~ -131 to +63 m, and r2 from 0.85 - 0.97 and bias from -119 to +101m, respectively).