Abstract View
Enhanced Reactivity in Droplets Relative to Bulk Solution Studied by Droplet Assisted Ionization Mass Spectrometry
YAO ZHANG, Murray Johnston, University of Delaware
Abstract Number: 364
Working Group: Aerosol Chemistry
Abstract
Droplet Assisted Ionization (DAI) is a relatively new method for online analysis of aerosol droplets that enables measurement of the rate of an aerosol reaction. It is an inlet ionization method, where ions are formed when droplets pass through a temperature-controlled capillary inlet to a mass spectrometer. Here, we used DAI to study the reaction of carbonyl functionalities in secondary organic aerosol (SOA) with Girard’s T (GT) reagent. Varying the droplet transit time between the atomizer and mass spectrometer allowed the reaction rate constant to be determined, which was found to be 4 orders of magnitude faster than what would be expected from bulk solution kinetics. Mechanisms of reaction acceleration on the droplet were investigated by varying DAI conditions including: i) increasing temperature applied on the capillary inlet, ii) decreasing the relative humidity of the air surrounding the droplets in between the atomizer and the mass spectrometer, and iii) varying the size of the droplets. It was found that the product formation was enhanced by heating the capillary inlet and decreasing the relative humidity of the air, suggesting that removing water from the droplets increased the reaction rate. Decreasing the droplet diameter increases the surface to volume ratio and can distinguish reaction on the particle surface from that in the bulk volume. The results suggest that reaction on the droplet surface plays an important role to increase the reaction rate in droplets relative to bulk solution.