Diagnosing the stratospheric proportion in tropospheric ozone using triple oxygen isotopes as tracers

Using a multistep nitrite-coated filter-pack system for sampling, we determined the seasonal variations in the triple oxygen isotopic composition ( Δ 17 O) of tropospheric ozone (O 3 ) in the terminal positions ( Δ 17 O term (O 3 )) in the cities Nagoya and Niigata (Japan) in the eastern Asia region to quantify the mixing ratio of stratospheric O 3 within the total tropospheric O 3 supplied 10 by stratosphere–troposphere transport (STT). In Nagoya, diurnal variations have also been studied. Both the average Δ 17 O term (O 3 ) and their 1σ variation ranges agreed well with previous studies, (37.5 ± 1.4) ‰ in Nagoya and (37.0 ± 1.7) ‰ in Niigata. The average difference in Δ 17 O term (O 3 ) between daytime (higher) and nighttime (lower) was (1.4 ± 0.7) ‰ (1σ) in Nagoya, which was responsible for the formation of a stable boundary layer at night, reducing mixing with high Δ 17 O term (O 3 ) from the free troposphere. We also found a significant correlation between 7 Be activity concentrations and the Δ 17 O term (O 3 ), implying that STT was responsible 15 for the elevated Δ 17 O term of O 3 in the troposphere. By using the relationship between the reciprocal of concentrations and Δ 17 O term of tropospheric O 3 , we estimated the Δ 17 O of stratospheric O 3 supplied through the STT ( Δ 17 O STT ), together with that produced through photochemical reactions at surface altitude ( Δ 17 O sur ). Moreover, using Δ 17 O STT and Δ 17 O sur , we estimated the mixing ratios of stratospheric O 3 (i.e., O 3 produced in the stratosphere and supplied to the troposphere through STT) in each tropospheric O 3 ( f STT ), as well as the absolute concentrations of stratospheric O 3 supplied through STT in the troposphere ( C STT (O 3 )). The C STT (O 3 ) 20 exhibited minimum values in summer ((5.3 ± 1.0) ppb) and maximum values in late winter to spring ((15.9 ± 2.1) ppb). Although the f STT values were higher than those estimated using the chemistry climate models from past studies, the trends of the seasonal variations were consistent with them. We concluded that Δ 17 O successfully provided observational constraints on the STT of O 3 . be explained by a simple mixing between stratospheric O 3 and tropospheric O 3 . If we extrapolated the linear correlation to stratospheric 7 Be activity concentration known to range from 160 mBq m –3 to 580 mBq m –3 (Kaste et al., 2002), the 255 stratospheric Δ 17 O term (O 3 ) increased from 117.5 ‰ to 332.3 ‰. Although the Δ 17 O term (O 3 ) showed a significant linear correlation In addition, we found that both concentrations and the Δ 17 O term of tropospheric O 3 can be explained by mixing between the three components: background O 3 in the troposphere, stratospheric O 3 supplied to the troposphere through STT, and O 3 produced in situ in the troposphere through photochemical reactions, and the estimated absolute concentrations of the stratospheric O 3 supplied through STT in the troposphere were highest in spring and lowest in summer. Moreover, the trend in seasonal variations of O 3 supplied through STT estimated in this study is in agreement with a previous study. 385