Estimation of secondary organic aerosol formation parameters for thevolatility basis set combining thermodenuder, isothermal dilution, and yieldmeasurements

Secondary organic aerosol (SOA) is a major fraction of the total organicaerosol (OA) in the atmosphere. SOA is formed by the partitioning ontopre-existent particles of low-vapor-pressure products of the oxidation ofvolatile, intermediate-volatility, and semivolatile organic compounds.Oxidation of the precursor molecules results in a myriad of organic products,making the detailed analysis of smog chamber experiments difficult and theincorporation of the corresponding results into chemical transport models(CTMs) challenging. The volatility basis set (VBS) is a framework that hasbeen designed to help bridge the gap between laboratory measurements andCTMs. The parametrization of SOA formation for the VBS has beentraditionally based on fitting yield measurements of smog chamberexperiments. To reduce the uncertainty in this approach, we developed analgorithm to estimate the SOA product volatility distribution, effectivevaporization enthalpy, and effective accommodation coefficient combining SOA yield measurements with thermograms (from thermodenuders) and areograms(from isothermal dilution chambers) from different experiments andlaboratories. The algorithm is evaluated with pseudo-data produced fromthe simulation of the corresponding processes, assuming SOA with knownproperties and introducing experimental error. One of the novel features ofour approach is that the proposed algorithm estimates the uncertainty in the predicted yields for different atmospheric conditions (temperature, SOAconcentration levels, etc.). The uncertainty in these predicted yields issignificantly smaller than that of the estimated volatility distributionsfor all conditions tested.

Automated summary

Secondary organic aerosol (SOA) is a major component of atmospheric organic aerosol (OA), and it is formed by the partitioning of low-vapor-pressure products of organic compound oxidation on pre-existent particles. The volatility basis set (VBS) is a framework designed to bridge the gap between laboratory measurements and chemical transport models (CTMs). In this study, an algorithm was developed to estimate the volatility distribution, effective vaporization enthalpy, and effective accommodation coefficient of SOA products by combining yield measurements, thermograms, and areograms from various experiments and laboratories. The algorithm was evaluated using simulated data and it showed smaller uncertainties in predicted yields compared to volatility distributions.