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.
This 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. VAP data can be used for calculating aerosol scattering and mass loading, estimating the impact of aerosol on clouds, and verifying aerosol-related quantities in models. The MERGEDSMPSUHSAS VAP is useful for sites lacking a scanning mobility particle sizer (SMPS). We recommend the MERGEDSMPSAPS product for sites with both an SMPS and an ultra-high-sensitivity aerosol spectrometer (UHSAS).
This VAP re-calibrates 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 (ACSM), literature optical constants, 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 improve the VAP performance.
Please note: MERGEDSMPSUHSAS does not adjust the particle counts from either the SMPS or UHSAS. If there are problems with the particle number counts in the input data, the merged distribution will be lower quality. The VAP also does not make corrections for possible artifacts in the UHSAS data due to changes in the gain stages used to measure scattering for different sized particles.
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