New Aerosol Optical Depth Data Available for 4 ARM Sites

Published: 22 February 2025

A plot of aerosol optical depths shows six different jagged lines representing 415, 500, 615, 673, 870 nm, and 1625 nm over an eight-hour period. Overall, the lines descend as the day goes on. — The colors represent aerosol optical depths measured at wavelengths of 415, 500, 615, 673, 870, and 1625 nanometers (nm) with the multifilter rotating shadowband radiometer on December 13, 2023, in La Jolla, California, during the EPCAPE campaign. Data plot is by Krista Gaustad, Pacific Northwest National Laboratory.

The Aerosol Optical Depth (AOD) value-added product derived from 7-channel multifilter rotating shadowband radiometer (MFRSR) measurements is now available for the Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) in La Jolla, California; the Surface Atmosphere Integrated Field Laboratory (SAIL) campaign near Crested Butte, Colorado; and the North Slope of Alaska (NSA) and Eastern North Atlantic (ENA) atmospheric observatories.

AOD is the measure of the total aerosol burden in a vertical column of the atmosphere. The value-added product, known as AOD-MFRSR, reports cloud-screened AOD from the direct normal irradiance measured by MFRSRs at the Atmospheric Radiation Measurement (ARM) User Facility’s ground-based sites.

AODs are calculated at wavelengths of 415, 500, 615, 673, 870, and 1625 nanometers (nm). The 940 nm channel is used to retrieve columnar abundances of water vapor.

ARM finished adding the near-infrared 1625 nm channel to its MFRSRs and other ground-based shortwave spectral instruments in fiscal year 2021. The longer wavelength allows for improved retrievals of aerosol and cloud properties. For example, it helps constrain the size distribution of large aerosol particles, resulting in more accurate retrievals of aerosol optical properties.

Scientists use AOD measurements to evaluate aerosol radiative forcing in earth system models. Because AOD is a measure of the aerosol burden in the atmosphere, AOD-MFRSR also allows a user to analyze variability of aerosol loading.

AOD-MFRSR 7-channel production data are available for:

the EPCAPE ARM Mobile Facility site on the Ellen Browning Scripps Memorial Pier in La Jolla from February 15, 2023, through February 14, 2024
the SAIL ARM Mobile Facility site in Gothic, Colorado, from September 1, 2021, through June 16, 2023
the NSA central facility at Utqiaġvik (formerly Barrow) from September 27, 2021, through May 31, 2024
the ENA on Graciosa Island in the Azores from April 15, 2021, through May 8, 2024.

AOD-MFRSR requires Langley calibration data as input. At the time of the latest AOD-MFRSR release, Langley data were unavailable for the ENA and NSA after June 1, 2024. Processing of ENA and NSA AOD-MFRSR data from June 1 onward will be completed once the Langley data are available.

More information about the data can be found on the AOD-MFRSR page.

Access the data in the ARM Data Center. (To download the data, first create an ARM account.)

For questions or to report data problems, please contact ARM translator John Shilling or developers Erol Cromwell and Krista Gaustad.

Data can be referenced as doi:10.5439/1756632.

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ARM is a DOE Office of Science user facility operated by nine DOE national laboratories.