Figure 1: Experimental setup for the product studies.
Product studies are performed Related to the investigations of radical and non-radical oxidation processes of organic compounds in the aqueous particle phase also. For the photochemical formation of radicals the sample is either irradiated continuously by a lamp (Figure 1) or with pulses of an excimer laser. The advantage of an irradiation with a lamp is the simulation of ambient conditions since only low concentrations of radicals are present in cloud droplets and organic compounds are slowly degraded.
Contrary to that, a high concentration of radicals is formed from the irradiation with a high energy UV laser pulse. Reaction products with carbonyl functions are detected with the help of HPLC-MS or GC-MS, whereas small organic acids are determined with capillary electrophoresis (CE-UV).
A recent research topic is the degradation of isoprene oxidation products with hydroxyl and sulfate radicals in the aqueous phase. Isoprene is a volatile compound which is emitted in high amounts into the troposphere by plants and gets degraded by oxidants in the gas phase. The oxidation products are less volatile and can partition into the aqueous particle phase. Due to the reaction of these compounds with radicals low volatile species are formed, e.g., organosulfates, which remain in the particle phase and contribute to the formation of secondary organic aerosol (SOA).