The Atmospheric Radiation Measurement (ARM) user facility currently operates at least four instruments that measure a portion of the ambient aerosol size distribution. Most users are interested in the entire size distribution or a portion of the size distribution that extends across the measurement range of multiple instruments. However, merging these distributions is not trivial because the instruments all employ different measurement principles and, in most cases, report data as a function of different representations of the aerosol diameter.
ARM recently released a value-added product (VAP) that merges aerosol size distributions from the scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS). Production data from the MERGEDSMPSAPS VAP are now available for the following ARM sites:
- the ongoing Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) in La Jolla, California
- the 2021–2022 TRacking Aerosol Convection interactions ExpeRiment (TRACER) near Houston, Texas
- the Southern Great Plains (SGP) extended facility E13 near Lamont, Oklahoma, from November 2016 to within a week of the current date.
The MERGEDSMPSAPS VAP is useful for scientists who need a representation of the aerosol size distribution in the particle diameter range of approximately 10–20,000 nanometers. Get additional details about the VAP on the MERGEDSMPSAPS web page.
To improve the quality assurance/quality control in the MERGEDSMPSAPS data, ARM developed a new VAP that applies additional quality flags using machine learning (ML) models trained on hand-labeled MERGEDSMPSAPS data. Evaluation data from the new MERGEDSMPSAPSML VAP are now available for SGP E13 from November 2016 to August 2023. Learn more about the VAP on the MERGEDSMPSAPSML page.
In addition, ARM produced a new VAP that merges aerosol size distributions from the SMPS and ultra-high-sensitivity aerosol spectrometer (UHSAS). The MERGEDSMPSUHSAS VAP is useful for scientists who need a representation of the aerosol size distribution in the particle diameter range of approximately 10–1,200 nanometers at sites without an APS. Currently, evaluation data are available for ARM’s Eastern North Atlantic atmospheric observatory in the Azores, Portugal, from November 2022 to August 2023.
MERGEDSMPSUHSAS recalibrates the UHSAS-measured optical diameter to account for the differences in ambient and calibration (PSL) aerosol optical constants using the chemical composition measured by the co-located aerosol chemical speciation monitor, optical constants in literature, and Mie theory. The VAP converts the UHSAS bin structure into the native SMPS bin structure to maintain constant size bin spacing across the entire size distribution. In addition, the VAP calculates integrated number, surface area, and volume concentrations across the entire size distribution. Data are averaged to a 1-hour time resolution to improve the signal at low particle counts and to improve the VAP performance.
Find more information about this VAP on the MERGEDSMPSUHSAS web page.
Scientists can use the merged aerosol size distribution VAPs for calculating aerosol scattering and mass loading, estimating the impact of aerosol on clouds, and verifying aerosol-related quantities in models.
Please note: None of the VAPs adjust the particle counts from the instruments. If there are problems with the particle number counts in the input data, the merged distribution will be lower quality. In addition, MERGEDSMPSUHSAS does not correct for possible artifacts in the UHSAS data due to changes in the gain stages used to measure scattering for different-sized particles. MERGEDSMPSUHSAS is useful for sites lacking an APS, but MERGEDSMPSAPS and MERGEDSMPSAPSML are recommended over MERGEDSMPSUHSAS when available.
Access the merged size distribution products in the ARM Data Center. (To download the data, first create an account.)
Feedback on the VAP data and their quality is encouraged to help improve these products. To provide feedback, ask questions, or report data problems, please contact ARM translator John Shilling or VAP developer Max Levin.
Data can be referenced as doi:10.5439/1871375 for MERGEDSMPSAPS, doi:10.5439/1992332 for MERGEDSMPSAPSML, and doi:10.5439/1984053 for MERGEDSMPSUHSAS.
# # #ARM is a DOE Office of Science user facility operated by nine DOE national laboratories.