Humidified single-scattering albedometer (H-CAPS-PM_SSA): Design, data analysis, and validation

Journal Article · Tue Mar 23 00:00:00 EDT 2021 · Aerosol Science and Technology

DOI:https://doi.org/10.1080/02786826.2021.1895430· OSTI ID:1772827

Carrico, Christian M.  ^[1]; Capek, Tyler J.  ^[2]; Gorkowski, Kyle J.  ^[3]; Lam, Jared T. ^[4]; Gulick, Sabina  ^[4]; Karacaoglu, Jaimy ^[1]; Lee, James E.  ^[3]; Dungan, Charlotte  ^[1]; Aiken, Allison C.  ^[3]; Onasch, Timothy B.  ^[5]; Freedman, Andrew  ^[5]; Mazzoleni, Claudio  ^[6]; Dubey, Manvendra K.  ^[3]

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1. New Mexico Institute of Mining and Technology, Socorro, NM (United States)
2. Michigan Technological Univ., Houghton, MI (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
4. New Mexico Institute of Mining and Technology, Socorro, NM (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
5. Aerodyne Research, Inc., Billerica, MA (United States)
6. Michigan Technological Univ., Houghton, MI (United States)

In this work, we report the development and validation of a new humidified aerosol single-scattering albedometer to quantify the effects of water uptake on submicrometer particle optical properties. The instrument simultaneously measures in situ aerosol light extinction (σ_ep) and scattering (σ_sp) using a cavity-attenuated phase shift-single scattering albedo particulate matter (PM) monitor (CAPS-PM_SSA, Aerodyne Research, Inc., Billerica, MA, USA). It retrieves by difference aerosol light absorption (σ_ap) and directly quantifies aerosol single-scattering albedo (SSA), the aerosol “brightness.” We custom built a relative humidity (RH) control system using a water vapor-permeable membrane humidifier and coupled it to the CAPS-PM_SSA to enable humidified aerosol observations. Our humidified instrument (H-CAPS-PM_SSA) overcomes problems with noise caused by mirror purge-flow humidification, heating, and characterizing cell RH. Careful angular truncation corrections in scattering, particularly for larger particles, were combined with empirical observations. Results show that the optimal operational size to be D_p < 400 nm. The H-CAPS-PM_SSA was evaluated with several pure single-component aerosols including ammonium sulfate ((NH₄)₂SO₄), absorbing nigrosin, and levoglucosan, an organic biomass smoke tracer. The measured σ_ep, σ_sp, and the derived optical hygroscopicity parameter (κ) for size-selected ammonium sulfate are in good agreement with literature values. For dry size-selected nigrosin in the 100 < D_p < 400 nm range, SSA values increased from ~0.3 to 0.65 with increasing D_p. The enhancement in nigrosin σ_ap at RH = 80% was a factor of 1.05–1.20 relative to dry conditions, with the larger particles showing greater enhancement. SSA increased with RH with the largest fractional enhancement measured for the smallest particles. For polydisperse levoglucosan, we measured an optical κ of 0.26 for both light extinction and scattering and negligible absorption. Our new instrument enables reliable observations of the effects of ambient humidity on mixed aerosol optical properties, particularly for light-absorbing aerosols whose climate forcing is uncertain due to measurement gaps.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Atmospheric Radiation Measurement (ARM) Data Center
• Sponsoring Organization: USDOE Office of Science (SC), Workforce Development for Teachers and Scientists (WDTS)
• Contributing Organization: PNNL, BNL, ANL, ORNL
• Grant/Contract Number: KP1701010; 1832813; AC52-06NA25396
• OSTI ID: 1772827
• Journal Information: Aerosol Science and Technology, Vol. 55, Issue 7; ISSN 0278-6826
• Publisher: American Association for Aerosol Research
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES