Diurnal changes of singlet oxygen like oxidants concentration in polluted ambient air

The long-term measurement of singlet oxygen like oxydants (SOLO) in polluted ambient air by use of the chemical determination method with α-terpinene (Ter) as a substrate was carried out. α-Terpinene endoperoxide, ascaridole (Asc), was produced by the reaction of SOLO with Ter in a similar manner to singlet oxygens (1O2). Asc formed was analyzed by gas chromatography-mass fragmentgraphy with selected ion monitoring mode.The concentration of SOLO in sample air was calculated from the amount of Asc determined, and expressed as O2 in active state. The concentration of 4 – 21 ppb of SOLO was detected in the daytime, and it reached to the maximum at around noon. SOLO were also detected in the nighttime and its concentration reached to the maximum at around midnight. The pattern of diurnal change of SOLO concentration was apparently different from that of photochemical oxidants including ozone, but identical with that of NOx. SOLO are not conventional photochemical oxidants such as ozone, but must be α-terpinene endoperoxide producible oxydants having similar reactivity to 1O2 and probably including 1O2 themselves.