Study on photochemical degradation of nonanal-an odorant in gas phase by vacuum ultraviolet

Key words: 
• odorous substances /
• n-nonanal /
• vacuum ultraviolet /
• photochemical degradation /
• indoor air

Abstract: The ATD-GC (automatic thermal desorptiongas chromatography) method was established for qualitative and quantitative analysis of n-nonanal, which was used to study the photochemical degradation of low concentration n-nonanal in the gas phase induced by vacuum ultraviolet. It was showed that the degradation rate of n-nonanal was little influenced by its inlet concentration, and the reaction followed the first-order kinetics with the apparent first-order reaction rate constant of 2.3 min-1 when the inlet concentration was in the range 0.13～1.74 mg/m3. The removal rate of n-nonanal decreased with increasing relative humidity for both the highand low-inlet concentration cases, but with further increases of relative humidity, they behaved differently: the removal rate of n-nonanal in the low-inlet-concentration case changed little while in the high-inlet-concentration case it decreased first and then increased again. n-nonanal could be photolyzed in dry pure nitrogen atmosphere and the degradation rate increased with the increasing humidity. The effects of different carrier gases were investigated and compared. The degradation rate of n-nonanal was in the following sequence: N2 2. It was suggested that in the process of vacuum ultraviolet-induced photochemical degradation the direct photolysis, photo-generated hydroxyl radicals and oxygen atom/ozone all contribute to the removal of n-nonanal and these three mechanisms interact with each other.