Results of the Second DOE ARM Aerosol Chemical Speciation Monitor (ACSM) users meeting

Description

The second DOE ARM Aerosol Chemical Speciation Monitor (ACSM) users meeting was held on September 18 and 19, 2018 at Aerodyne Research, Inc., to discuss the ACSM data and build on the progress made at the first users meeting in April 2017. Since the first meeting, the two recommendations of the group have been used to evaluate the data and data processing. The mentor compared observed versus predicted particulate ammonium (NH4+) mass loadings. The results show that the measured relative ionization efficiencies of NH4 and SO4 used in the past are too high and too low respectively. RIE for NH4 should be about 5, while the RIE for SO4 should be about 0.8. These are significantly different than the values as the averages measured over 6 years at SGP. Use of the RIE for SO4 of 1 and for NH4 of 5 result in 1 to 1 slope of the measured NH4 to predicted NH4 correlation plots consistent with a neutralized aerosol. New calibration methods have been incorporated in the operational software that allow for longer equilibration times and measurement of both filter and switching cycles during calibration. Implementation of these protocols have resulted in better values for the two RIEs. These data will be presented. The mentor also studied ACSM mass loadings versus mass derived from particle size measurements of the SMPS and UHSAS. These results will be presented along with recommendations for data processing and quality control methods to be implemented by the data center.