Mass transfer effects in hygroscopic measurements of aerosol particles

Hygroscopicity and phase transitions were measured with deposited particles of ammonium sulfate (AS), ammonium nitrate (AN), malonic acid (MA), glutaric acid (GA), glyoxylic acid (GlyA), as well as two mixed particle systems AS-MA and AS-GA using micro-Raman spectroscopy. Hygroscopicity was presented in terms of water-to-solute mass ratios, which were obtained from the integrated area ratios of the Raman water band to a distinct solute peak. Deliquescence and crystallization were confirmed by abrupt changes in the Raman peak positions and the full-widthhalf-heights of distinct solute peaks. The results for AS, AN, MA, and GA agreed well with literature reports and model predictions. For GlyA, we detected the Raman water band at near 0% RH, indicating that the spectral technique is sensitive for hygroscopic measurements at very low RH. Additional spectral feature at ∼0% RH was also observed. In the case of more complicated ASdicarboxylic acid mixed systems, the partial phase transitions of the organic components were identified using the intensity ratios of aqueous to solid C=O peaks. AS-MA particles did not completely crystallize and gradual water uptake with increasing RH from 3% was observed. Moreover, it was found that AS-GA particles showed step-wise crystallization in which the AS fraction crystallized prior to the GA fraction. The measured water content and complete DRH of both mixed systems were consistent with the published values. The results show the utility of micro-Raman spectroscopic analysis in studying hygroscopicity and phase characterizations of the chemical species in mixed particles.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Water Content and Phase Transitions in Particles of Inorganic and Organic Species and their Mixtures Using Micro-Raman Spectroscopy

Yeung

Chan

2010

“…Although elemental analysis of the particular sea salt employed in these studies is not available, sea salt in general consists of 48.7% Cl -, 41.9% Na + , 4.7% Mg 2+ , 2.5% SO 2-4 , 0.9% Ca 2+ , 0.9% K + on a mole basis, accounting for 99.7% of the constituents (Stumm and Morgan 1996). NaCl and AS particles are widely used for calibration of growth factors measured by HTDMAs (Chan and Chan 2005;McFiggans et al 2006). The DRH of NaCl is 75% and of AS is 79.5% at 298 K for bulk materials (Martin 2000).…”

Section: Aerosol Generationmentioning

confidence: 99%

The 1-by-3 Tandem Differential Mobility Analyzer for Measurement of the Irreversibility of the Hygroscopic Growth Factor

Rosenoern¹,

Paulsen²,

Martin³

2009

A new instrument, namely the 1 × 3 tandem differential mobility analyzer (1 × 3-TDMA), has been developed. Its primary measurement is the irreversibility of the hygroscopic growth factor of aerosol particles. The instrument uses the hysteresis of phase transitions to infer the solid or aqueous state of the particles. A first DMA passes particles of a selected electric mobility at relative humidity RH 0 . Exiting this DMA, the particles are split into three separate flows. The first flow is exposed to RH 0 → (RH 0 + δ) → RH 0 in a deliquescence test before passing through a second DMA that is set to the same electric mobility as the first DMA. The second flow passes directly to a third DMA without change in RH, thereby serving as a reference arm. This DMA is also set to the same electric mobility as the first DMA. The transmission ratio of the 1 × 3-TDMA is defined as the particle concentration passing the deliquescence test divided by that passing through the reference arm. The transmission ratio is unity in the absence of deliquescence and zero when a phase transition occurs, at least for ideal instrument performance in application to a test aerosol of fully deliquesceable particles. For the third flow passing out of the first DMA, an efflorescence test is run by using the RH profile of RH 0 → (RH 0 − δ) → RH 0 before passing through a fourth DMA. A full data set for the 1 × 3-TDMA is obtained by scanning RH 0 , typically from 20 to 85%. In the present paper, the 1 × 3-TDMA instrument is described, and laboratory data are presented for the phase transitions of externally mixed aerosols of aqueous and solid sodium chloride particles, aqueous and solid ammonium sulfate particles, and their mixtures, as well as a mixture of aqueous and solid sea salt particles. The observed transmission ratio is compared to a model analysis. The intent behind the development of this instrument is to deploy it for field measurements and use observations of

“…The humidity exchange cells and subsequent tubing provide exposure time of 6-9 s which is sufficient for most aerosol particles to achieve humidity equilibrium with surrounding air (Chuang 2003;Chan and Chan 2005); additional exchangers or line sections could be used to increase exposure time.…”

Section: Instrumentation and System Designmentioning

confidence: 99%

“…Aerosol water uptake and subsequent changes in aerosol properties have been studied in three categories: (1) change in size (Chan and Chan 2005), (2) light scattering enhancement (Covert et al 1972;Fierz-Schmidhauser et al 2010), and (3) change in physical and chemical properties, such as refractive index (Wang and Rood 2008). The current state of f(RH) studies pertaining to climate research is summarized nicely in Yan et al (2009).…”

Section: Introductionmentioning

confidence: 99%

Development of a New Airborne Humidigraph System

Pekour

Schmid

Chand

et al. 2013

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.