Abstract
Abstract. Individual particles that on a mass basis consist dominantly of the components ammonium sulfate, oxygenated 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. Specifically these variables were used to predict the critical relative humidity of 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 88% of the measurements, ERH within 5% for 84% of the measurements, and DRH within 5% for 94% 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 values predicted by the parameterisations using the measured org:sulf and O:C ratios as the input variables.
Highlights
Atmospheric aerosol particles have many important roles in the Earth system
The relative humidity at which liquid-liquid phase separation (SRH), efflorescence (ERH), and deliquescence (DRH) occurred in 11 different oxygenated organic-ammonium sulfate systems was studied with an optical microscope coupled to a temperature controlled flow-cell (Pant et al, 2006; Ciobanu et al, 2009; Bodsworth et al, 2010)
The applicability of the derived parameterisations for predicting the phase transitions of multi-component oxygenated organic-sulfate mixtures was tested using secondary organic material (SOM) that was mixed with sulfate and water in individual particles
Summary
Atmospheric aerosol particles have many important roles in the Earth system. Examples include their feedback mechanisms to climate change, their links to the biogeochemical cycles of many elements, and their effects on regional visibility and human health (Finlayson-Pitts and Pitts, 1997; Ravishankara, 1997; Martin et al, 2004; Pope and Dockery, 2006; Seinfeld and Pandis, 2006; Forster et al, 2007). Since the sulfate fraction is often partially or fully neutralised by ammonium (Dibb et al, 1996; Huebert et al, 1998; Talbot et al, 1998; Dibb et al, 2000; Lee et al, 2003), mixed organic-ammonium sulfate particles constitute an important class of atmospheric aerosol particles
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
