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

摘要

Individual particles that on a mass basis consist dominantly of thecomponents ammonium sulfate, oxygenated organic material, and water are a common classof submicron particles found in today's atmosphere. Here we use (1) theorganic-to-sulfate (org:sulf) mass ratio of the overall particle and (2) theoxygen-to-carbon (O:C) elemental ratio of the organic component as inputvariables in parameterisations that predict the critical relative humidity ofseveral different types of particle phase transitions. Specifically these variables wereused to predict the critical relative humidity of liquid-liquid phase separation (SRH),efflorescence (ERH), and deliquescence (DRH). Experiments were conducted by optical microscopy for 11different 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 theliterature, were used to develop the parameterisations SRH(org:sulf, O:C),ERH(org:sulf, O:C), and DRH(org:sulf, O:C). The parameterisations correctlypredicted SRH within 15% RH for 88% of the measurements, ERH within 5% for84% of the measurements, and DRH within 5% for 94% of the measurements.The applicability of the derived parameterisations beyond the training dataset was tested against observations for organic-sulfate particles produced inan environmental chamber. The organic component consisted of secondaryorganic material produced by the oxidation of isoprene,α-pinene, and β-caryophyllene. The predictions of theparameterisations were also tested against data from the Southern GreatPlains, Oklahoma, USA. The observed ERH and DRH values for both the chamberand field data agreed within 5% RH with the values predicted by theparameterisations using the measured org:sulf and O:C ratios as the inputvariables.