Development of a New Airborne Humidigraph System

Abstract

The hygroscopic behavior of atmospheric aerosols complicates modeling and measurements of aerosol properties adding significant uncertainty to our best estimates of the direct effect aerosols exert on the radiative balance of the atmosphere. Airborne measurements of aerosol hygroscopicity are particularly challenging but critically needed. This motivated the development of a new system designed to measure the dependence of the aerosol light scattering coefficient (σ sp ) on relative humidity (RH), known as f(RH), in real-time on an aerial platform.The new instrument has several advantages over existing systems. It consists of three integrating nephelometers and humidity conditioners for simultaneous measurement of the σ sp at three different RHs. The humidity is directly controlled in exchanger cells without significant temperature disturbances and without particle dilution, heating, or loss of volatile compounds. The singlewavelength nephelometers are illuminated by LED-based light sources thereby minimizing heating of the sample stream. The flexible design of the RH conditioners, consisting of a number of specially designed exchanger cells (driers or humidifiers), enables us to measure f(RH) under hydration or dehydration conditions (always starting with the aerosol in a known state) with a simple system reconfiguration. These exchanger cells have been characterized for losses of particles using latex spheres and laboratory generated ammonium sulfate aerosols. The performance of this instrument has been assessed aboard DOE's G-1 research aircraft during test flights over California, Oregon, and Washington.

Hyperspectral aerosol optical depths from TCAP flights

“…Details of performance, calibration, and operations of this system are provided by Pekour et al . []. They were calibrated using three gases, as described above for the TSI nephelometer.…”

Satellite-Surface Perspectives of Air Quality and Aerosol-Cloud Effects on the Environment: An Overview of 7-SEAS/BASELInE

“…In addition, water uptake of aerosols is a key factor influencing their growth in size and deposition inside the humid respiratory tract and exact corresponding health effects (Löndahl et al, 2009;Engelhart et al, 2012;Martonen et al, 2003). Thus, one compelling reason for using in-situ measurements to fully study the aerosol hygroscopicity is that none of the current operational satellite algorithms retrieve hygroscopic properties of ambient aerosols; however, these properties have been identified by modeling studies as a significant source of uncertainty when predicting their influences on air quality and radiative forcing on regionalto-global scales (e.g., Wang and Martin, 2007;Achtert et al, 2009;Pekour et al, 2012;Titos et al, 2014). Petters and Kreidenweis (2007) derived a one-parameter model, the so-called κ-Köhler theory, where the hygroscopicity parameter (κ) represents a quantitative measure of aerosol water uptake characteristics and CCN activity.…”

Airborne Aerosol in Situ Measurements during TCAP: A Closure Study of Total Scattering

“…Figure 3 illustrates that the aerosol chemical composition on 21 July 2012 was dominated by organic matter (OM); dominance of OM (generally greater than 70%) was observed for all TCAP flights [45]. The total scattering coefficient at three wavelengths (0.45, 0.55, 0.7 µm) was measured at dry (RH < 20%) conditions using a TSI integrating nephelometer (Figure 4), while the light scattering hygroscopic growth, known as f(RH), was measured using a humidification system at three defined RHs (near 45%, 65% and 90%) at a single wavelength (0.525 µm) [51]. Similar to Shinozuka et al [52], we adjust the f(RH) obtained at the 0.525 µm wavelength to the nephelometer wavelengths (0.45, 0.55, 0.7 µm) by multiplying the obtained f(RH) by 0.98, 1.01 and 1.04, respectively.…”