18 January 2024
Currently, ARM operates at least four different 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 as the instruments all employ different measurement principles and, in most cases, report data as a function of different representations of the aerosol diameter. The VAP merges size distributions measured by the scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS).
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This VAP is useful for scientists who need a representation of the aerosol size distribution from approximately 10–20,000 nm diameter. 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.
This VAP merges size distributions measured by the SMPS and APS using the method outlined by Beddows et al. 2010, with some modifications. The VAP converts the APS aerodynamic diameter to a mobility diameter and re-bins the data into the native SMPS bin structure so that constant dlogDp is maintained across the entire size distribution. The VAP also calculates integrated number, surface area, and volume concentrations across the entire size distribution. Data are averaged to a 1-hour time resolution to improve signal at low particle counts and improve the VAP performance. Note that the VAP does not adjust the particle counts from either the SMPS or APS. If there are problems with the particle number counts in the input data, particularly in the region where the instrument sizing overlaps, the merged distribution will be lower quality.
Reference: Beddows DCS, M Dall’osto, and RM Harrison. 2010. “An Enhanced Procedure for the Merging of Atmospheric Particle Size Distribution Data Measured Using Electrical Mobility and Time-of-Flight Analysers.” Aerosol Science and Technology, 44(11), https://doi.org/10.1080/02786826.2010.502159.