Predicting the relative humidities of liquid-liquid phase separation, efflorescence, and deliquescence of mixed particles of ammonium sulfate, organic material, and water using the organic-to-sulfate mass ratio of the particle and the oxygen-to-carbon elemental ratio of the organic component

Abstract

Individual particles that on a mass basis consist dominantly of the components ammonium sulfate, organic material, and water are a common class of submicron particles found in today's atmosphere. Here we use (1) the organic-to-sulfate (org:sulf) mass ratio of the overall particle and (2) the oxygen-to-carbon (O:C) elemental ratio of the organic component as input variables in parameterisations that predict the critical relative humidity of several different types of particle phase transitions. These transitions include liquid-liquid phase separation (SRH), efflorescence (ERH), and deliquescence (DRH). Experiments were conducted by optical microscopy for 11 different oxygenated organic-ammonium sulfate systems covering the range 0.1 < org:sulf <12.8 and 0.29 < O:C < 1.33. These new data, in conjunction with other data already available in the literature, were used to develop the parameterisations SRH(org:sulf, O:C), ERH(org:sulf, O:C), and DRH(org:sulf, O:C). The parameterisations correctly predicted SRH within 15 % RH for 86 % of the measurements, ERH within 5 % for 86 % of the measurements, and DRH within 5 % for 95 % of the measurements. The applicability of the derived parameterisations beyond the training data set was tested against observations for organic-sulfate particles produced in an environmental chamber. The organic component consisted of secondary organic material produced by the oxidation of isoprene, α-pinene, and β-caryophyllene. The predictions of the parameterisations were also tested against data from the Southern Great Plains, Oklahoma, USA. The observed ERH and DRH values for both the chamber and field data agreed within 5 % RH with the value predicted by the parameterisations using the measured org:sulf and O:C ratios as the input variables

Efflorescence upon humidification? X‐ray microspectroscopic in situ observation of changes in aerosol microstructure and phase state upon hydration

“…Above 80%, RH deliquescence occurs and strong water uptake is observed. This DRH of the mixed (NH 4 ) 2-x-y H x K y SO 4 /SOM particles (O:C of SOM = 0.6 ± 0.2; SOM:SO 4 2À mass ratio = 0.4 ± 0.1) is in agreement with the predictions by Bertram et al [2011]. The morphological appearance of the particle residue before (Figure 4b) and after ( Figure 4o) the full hydration and dehydration cycle appears similar.…”

Measuring Aerosol Phase Changes and Hygroscopicity with a Microresonator Mass Sensor

“…Ambient particles generally contain complex mixtures of components, including a sizable organic fraction. A number of studies suggest that this tends to suppress deliquescence and efflorescence of individual components 7,8,56 , including the mixed MA/NaCl particles with low fk here. We therefore anticipate that generally small fk corrections might be required for ambient samples, which could either be based on an average "ambient fk" from extensive field testing, or neglected.…”

“…In practice, many aerosols including some single-component organic particles and most particles containing complex mixtures of compounds do not effloresce, meaning that distinct efflorescence and deliquescence behavior is not observed, even if it is thermodynamically predicted. 7,8 A common approach to quantifying hygroscopic growth is in terms of an aerosol mass growth factor (GF), m/m0, where the aerosol mass at a given RH (m) is normalized to the dry mass (m0). A number of analytical methods exist to assess aerosol water uptake.…”

Ice cloud formation potential by free tropospheric particles from long‐range transport over the Northern Atlantic Ocean

“…Only the first ice nucleation event was reported since the presence of ice could lead to changes in RH ice above the particles at the low cooling rates used in these measurements. Although activation of all particles cannot be achieved by this method, the first ice formation event represents the precise thermodynamic conditions at which air containing a similar particle population would initiate ice crystal formation and, in addition, allows for the unambiguous identification of the ice nucleation process (IMF and DIN), deliquescence, or liquid-liquid phase separation [Bertram et al, 2011;Wise et al, 2012;Schill and Tolbert, 2013;. The optical microscope method intrinsically possesses high detection sensitivity, being able to determine activated fractions in the range of 10 À6 .…”