A Newly Designed and Constructed Instrument for Coupled Infrared Extinction and Size Distribution Measurements of Aerosols

Abstract

Although atmospheric particles are often non-spherical, Mie theory is commonly used to acquire aerosol optical depth, composition, and transport information from satellite retrievals. In the infrared (IR) region, the radiative effects of aerosols, usually modeled with Mie theory, are subtracted from satellite spectral data to determine key atmospheric and oceanic properties. To gain a better understanding of the infrared radiative effects of aerosols and the methods used to model them, an instrument has been designed to simultaneously measure infrared extinction spectra and particle size distributions obtained from a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). Infrared extinction spectra are simulated with Mie theory using the measured particle size distributions and available literature optical constants. As a result, the errors associated with using Mie theory to model the infrared extinction of mineral dust aerosol can be quantitatively examined. Initial results for this instrument are presented here. For ammonium sulfate, the Mie theory simulation is in good agreement with our measured extinction spectrum. This is in accordance with the nearly spherical shape of ammonium sulfate particles. However, for illite, an abundant clay mineral, there is poor agreement between the experimental spectrum and the Mie simulation. This result is attributed to particle shape effects.

High variability of the heterogeneous ice nucleation potential of oxalic acid dihydrate and sodium oxalate

“…Due to the lack of appropriate shape information, the dynamic shape factor χ was set to 1.0 in both cases. When assuming spherical particles with χ = 1, the mobility-equivalent diameter of the SMPS would be equal to d p (Hinds, 1999;Hudson et al, 2007). air over a heated reservoir of crystalline oxalic acid dihydrate (373 K). The gaseous oxalic acid/air mixture was then directed via stainless steel connection tubes into the AIDA chamber that was held at 228 K, thereby inducing the binary nucleation of oxalic acid and water.…”

“…Due to the lack of appropriate shape information, the dynamic shape factor χ was set to 1.0 in both cases. When assuming spherical particles with χ = 1, the mobility-equivalent diameter of the SMPS would be equal to d p (Hinds, 1999;Hudson et al, 2007). Fig.…”

“…Kanji et al (2008) have determined threshold relative humidities for the nucleation of a single ice particle on the ensemble of deposited particles as a function of the total particulate surface area. The surface area was varied by adjusting the total number of particles on the stage, typically from a few hundred to several 10 5 particles (Kanji and Abbatt, 2006). The measured critical ice saturation ratios ranged from about 1.10-1.25 for total particulate surface areas in the range of 2 × 10 −1 -6 × 10 −4 cm 2 .…”

Infrared Optical Constants of Organic Aerosols: Organic Acids and Model Humic-Like Substances (HULIS)

“…A multi-analysis aerosol reactor system (MAARS) was used to simultaneously measure aerosol size distributions and IR extinction spectra (Hudson et al 2007). Aerosols were formed by atomizing (TSI Inc., Model 3076) the solutions.…”

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

“…One disadvantage is that DEHS is a plasticiser so can attack plastic components. Oleic acid and ammonium sulphate have been tested, but the former reacts with oxygen and the latter does not form perfectly spherical aerosol (Dick et al, 1998;Hudson et al, 2007).…”