Measurement of the water cycle in a levitated ammonium sulfate particle

104

109

This paper describes the design and application of a pulsed cavity ring-down aerosol extinction spectrometer (CRD-AES) for insitu atmospheric measurement of the aerosol extinction coefficient and its relative humidity dependence. This CRD-AES measures the aerosol extinction coefficient (σ ep ) at 355 nm, 532 nm, 683 nm, and 1064 nm with a minimal size dependent bias for particles with diameter less than 10 μm. The σ ep at 532 nm is measured with an accuracy of 1% when extinction is ≥10 Mm −1 . The precision is limited by statistical fluctuations within the small optical volume and the time resolution of extinction at 2% uncertainty for various air mass types is evaluated. The CRD-AES is configured with two separate cavity ring-down cells for measurement of the extinction coefficient at 532 nm. This allows the determination of the RH dependence of extinction at 532 nm through independent RH control of the sample for each measurement. Gas phase absorption and minimization of potential interferences is also considered.

Section: Rh Dependencesupporting

confidence: 93%

Design and Application of a Pulsed Cavity Ring-Down Aerosol Extinction Spectrometer for Field Measurements

Baynard

Lovejoy

Pettersson

et al. 2007

104

109

“…The electrodynamic balance (EDB) (Richardson and Spann 1984;Cohen et al 1987;Tang et al 1995) and humidified tandem differential mobility analyzer (HTDMA) (McMurry and Stolzenburg 1989;Svenningsson et al 1997;Chan and Chan 2005;Swietlicki et al 2008) have been widely used to study the hygroscopic growth of suspended particles. However, these techniques give no direct information of the phase state of the particles' components.…”

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

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.

“…An advantage of the levitated single particle techniques is that the exact mass change of a droplet can be measured. These techniques have been widely used to study solution thermodynamics and chemistry of single component solutions Munkelwitz, 1977, 1984;Rubel, 1981;Richardson and Kurtz, 1984;Richardson and Spann, 1984;Tang et al, 1986;Cohen et al, 1987a;Chan et al, 1992) and multicomponent solutions (Tang et al, 1978;Spann and Richardson, 1985;Cohen et a]., 1987b;Chan et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

Determination of Water Activity in Ammonium Sulfate and Sulfuric Acid Mixtures Using Levitated Single Particles

Kim

Pun

Chan

et al. 1994

Water activities of ammonium sulfate-sulfuric acid termiued relative to the known properties at RH about mixtures with ammonium to sulfate molar ratios be-0.75-0.90. The data were compared with other meatween 0 and 2 were measured by a spherical void surements and the estimates from the Zdanovskiielectrodynamic levitator at relative humidities (RH) of Stokes-Robinson (ZSR) method and SCAPE, a newly 0.18-0.90. Since the composition of the solid particles developed gas-particle equilibrium model, and generis subject to uncertainty, solution properties were deally were found to be in good agreement.