Aqueous Atmospheric Species, a Dual Study: 1. Comparison of the Effects of Temperature, Oxygen Level, Ionic Strength, and pH on the Reaction of Benzene with Hydroxyl Radicals at the Air-water Interface to the Bulk Aqueous Phase. 2. Determination of Carbonyl Compounds in Fog Water Samples via Online Concentration and HPLC

Abstract

The air-water interface is the largest interface in the environment. Atmospheric droplets, such as fog, which can have an exceptionally high surface area-to-volume ratio, also have a large range of physical and chemical properties (e.g. temperature, pH, ionic strength, and chemical composition) based on location, time of day, and emission source. Unlike larger atmospheric droplets, which are predominately characterized by bulk aqueous phase conditions, reactions that take place in fog droplets are determined by both the bulk-aqueous phase and the air-water interface due to a high surface area-to-volume ratio. In order to have a greater understanding of atmospheric processes and the fate of environmental pollutants (e.g. benzene and other carbonyl compounds) in fog droplets, both laboratory and field studies are necessary. The reaction of benzene, a common primary atmospheric pollutant, with the hydroxyl radical, was studied in both a bulk-phase reactor and a thin film flow-tube reactor as a laboratory study. For both reactor systems, temperature, pH, ionic strength, and the concentration of oxygen were varied to simulate fog event conditions. Using the thin-film reactor, in particular, has the advantage in that the effect of both bulk and surface conditions on this model reaction can be obtained by adjusting the liquid volume over a given surface area inside the reactor. Volatile organic compounds (VOCs), like benzene, can also degrade in the environment by oxidation to form carbonyl compounds, which, like benzene, are also ubiquitous air, cloud, and fog water pollutants. Furthermore, they also form secondary organic aerosol (SOA) and are precursors to photochemical smog. In order to better understand fog/smog processes and characterization, fog water samples, collected in Baton Rouge, LA, were analyzed for aldehydes and ketones with a method adapted from U.S. EPA Method 8315A. By using a manual injection online concentration system, all liquid-liquid extraction and concentration steps from the original method were eliminated and the required sample volume was reduced. Doing so also shortened the procedure time and lowered the limit of detection.