The National Research Council has recommended a “network of networks” which builds upon already existing radiosonde launch sites, wind profilers, and lidars into a national network to address the current inadequacies in determining the Mixing Layer Height (MLH). They have stated that after sixty (60) years of remote sensing research, it is astounding that the MLH, an important meteorological variable, is not measured regularly throughout its diurnal cycle.
Due to the harmful effects on health caused by particulate matter and ozone, accurate forecasting of air quality conditions is needed for the public well-being. The MLH is one of the key diagnostics for identifying uncertainties in forecasting models as it contains most of the aerosols and its height determines the volume of the air available for pollutant dilution. Models with inaccurate MLHs will generally not predict surface pollutant concentrations correctly, likely an indication of inadequately simulated meteorological setup. Because of this, tools and methodologies that can accurately determine the height of the mixing layer are needed.
Full-range backscatter profiles measured by ceilometers and lidars can allow for the identification and potential justification of an air quality exceptional event. These instances include smoke transport and intrusion into the mixing layer, dust transport, etc. By creating an extensive network of remote sensing instrumentation (e.g., ceilometers, lidars, etc), exceptional events will become easily identifiable. In particular, the addition of established of a network of remote sensing instrumentation within the OTR (Ozone Transport Region) from state/local/educational agencies will be key to understanding the role of pollutant transport to surface ozone concentrations in the Northeast and Mid-Atlantic regions.
Furthermore, the US Environmental Protection Agency will require state and local air quality agencies to measure hourly MLH at the national Photochemical Monitoring Assessment Stations (PAMS), as is set forth in 40 CFR Part 58. The primary purpose for the hourly MLH under PAMS was driven by the state’s State Implementation Plan (SIP) modeling data needs. The PAMS requirement to measure the MLH is not limited to a particular technology and will likely be meet through the deployment of a combination of sophisticated instrumentation (ceilometers, lidars, Doppler wind lidars and radar wind profilers). A first step to developing a “network of networks” is to develop a common MLH algorithm that can be implemented across a heterogeneous network which includes ceilometer/lidars. Hence, centralized standardization of data outputs and retrievals is needed.
Areas of interest within the scope of EPA:
- Understanding the temporal evolution of the MLH, in particular the growth (morning rise) and decay (afternoon descent) of the MLH.
- Measurement-to-model simulation comparison which can aid in defining the most reliable and robust modeling meteorological and chemical schemes/constraints which best correlate with remote sensing observations.
- Models may have specific vertical and horizontal resolutions which may be coarser than available measurements. Quantifying these differences can be used to correctly relate observations and model simulation studies.
- Model land mask and land cover classifications will assign a water/land mask identity to each grid cell, and a respective land cover classification (e.g., urban land, grassland, water body, mixed forest, etc.). The incorrect classification of land surfaces can cause model simulations to incorrectly predict surface fluxes and therefore MLHs. Validation of the simulated MLHs with profiling observations can help identify challenging areas.
In past years, University of Maryland, Baltimore County (UMBC), and Howard University (HU) in collaboration with NOAA/NWS, and NOAA/NCEP, conducted a pilot study to utilize the full data profile of the NOAA/NWS ASOS ceilometer network. One of the objectives of that work was to define the technical details of the retrieval of aerosol mixing height as a proxy of the PBL height. This collaborative work is part of the NOAA Office of Education Cooperative Science Centers: Center for Earth System Sciences and Remote Sensing Technology (CESSRST) and NOAA Center for Atmospheric Sciences and Meteorology (NCAS-M). UMBC is a university partner on both of these centers led by City College of New York and Howard University, respectively. Research is aligned with CESSRST Atmospheric Hazards thematic research area and NOAA’s Weather Ready Nation efforts. Since 2016, the Ad-Hoc Ceilometer Evaluation Study (ACES) between the University of Maryland, Baltimore County (UMBC), and Environmental Protection Agency (EPA) has helped guide the EPA Enhanced Photochemical Assessment Monitoring Sites program new hourly MLH requirement.
A prototype network testbed of aerosol profilers between UMBC, Howard University, EPA and Maryland Department of the Environment (MDE) has been established. This prototype network will be a scalable demonstration in support of the EPA PAMS program and the MDE-Enhanced Monitoring Plan (EMP) capable of hosting data from other state/local agencies profiling sites implemented under the PAMS program, as well as academic institutions. This initial network will consist of remote sensing instrumentation deployed in the state of Maryland. Lidar/ceilometer remote sensing technology will be deployed at UMBC, Howard University Beltsville Research Center, and the Essex, Edgewood and Fairhill MDE Air Quality Monitoring Sites.
 National Research Council. 2009. Observing Weather and Climate from the Ground Up: A Nationwide Network of Networks. Washington, DC: The National Academies Press. https://doi.org/10.17226/12540.