Photochemical oxidation of di-n-butyl phthalate in atmospheric hydrometeors by hydroxyl radicals from nitrous acid

The photochemical oxidation of di-n-butyl phthalate (DBP) by (OH)-O-center dot radicals from nitrous acid (HONO) in atmospheric hydrometeors was explored by two techniques, steady-state irradiation, and laser flash photolysis (LFP). The effects of atmospheric liquid parameters on DBP transformation were systematically evaluated, showing that DBP does not react with HONO directly and (OH)-O-center dot-initiated reactions are crucial steps for consumption and transformation of DBP. Two reaction channels are operative: (OH)-O-center dot addition and hydrogen atom abstraction. The overall rate constant for the reaction of DBP with (OH)-O-center dot is 5.7 x 10(9) M-1 s(-1), and its specific rate constant for addition is 3.7 x 10(9) M-1 s(-1) determined by using laser flash photolysis technique. Comparing the individual reaction rate constant for aromatic ring addition with the total rate constant, the majority of the (OH)-O-center dot radicals (about 65%) attack the aromatic ring. The major transformation products were identified by GC-MS, and the trends of their yields derived from both ring addition and H-abstraction with time are discussed. These results provide important insights into the photochemical transformation of DBP in atmospheric hydrometeors and contribute to atmospheric aerosol chemistry.