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In this study we reexamine nearly four decades of in situ balloon-based stratospheric observations of SF6 and CO2 with an idealized model and reanalysis products. We use new techniques to account for the spatial and temporal inhomogeneity of the sparse balloon profiles and to calculate stratospheric mean ages of air more consistently from the observations with the idealized model. By doing so we are able to more clearly show and account for the variability of mean age of air throughout the bulk of the depth of the stratosphere. From an idealized model guided by the observations, we identify variability in the mean age due to the seasonal cycle of stratospheric transport, the quasi-biennial oscillation in tropical zonal winds, major volcanic eruptions, and linear trends that vary significantly with altitude. We calculate a negative mean age trend in the lowest 5 km of the stratosphere that agrees within uncertainties with a trend calculated from a set of chemistry climate model mean ages in this layer. The mean age trends reverse sign in the middle and upper stratosphere and are in agreement with a previous positive trend estimate using the same observational data set, although we have substantially reduced the uncertainty on the trend. Our analysis shows that a long time series of in situ profile measurements of trace gases such as SF6 and CO2 can be a unique and useful indicator of stratospheric circulation variability on a range of time scales and an important contributor to help validate the stratospheric portion of global chemistry climate models. However, with only SF6 and CO2 measurements, the competing effects on mean age between mean circulation and mixing (tropical entrainment) are not uniquely separable.

We have carried out monthly flask sampling using aircraft, in the altitude range of 0-7 km, over the boreal wetlands in Surgut (61°N, 73°E; since 1993) and a pine forest near Novosibirsk (55°N, 83°E; since 1997), both located in the West Siberian Lowland (WSL). The temporal variation of methane (CH4) concentrations at all altitudes at both sites exhibited an increasing trend with stagnation during 2000-2006 as observed globally from ground-based networks. In addition to a winter maximum as seen at other remote sites in northern mid to high latitudes, another seasonal maximum was also observed in summer, particularly in the lower altitudes over the WSL, which could be attributed to emissions from the wetlands. Our measurements suggest that the vertical gradient at Surgut has been decreasing; the mean CH4 difference between 5.5 km and 1.0 km changed from 64±5 ppb during 1995-1999 to 37±3 ppb during 2009-2013 (mean ± standard error). No clear decline in the CH4 vertical gradient appeared at Novosibirsk. Simulations using an atmospheric chemistry-transport model captured the observed decrease in the vertical CH4 gradient at Surgut when CH4 emissions from Europe decreased but increased from the regions south of Siberia, e.g., East and South Asia. At Novosibirsk, the influence of the European emissions was relatively small. Our results also suggest that the regional emissions around the WSL did not change significantly over the period of our observations.

The vertical distribution of isotopomers of N2O (14N15N16O, 15N14N16O, and 14N14N18O) in the lower and middle stratosphere was observed over Japan (39°N, 142°E) in 1999 using a balloon-borne cryogenic sampler and ground-based mass spectrometry. The abundance of the heavier isotopomers relative to 14N14N16O increased with altitude, while the mixing ratio of N2O decreased due to photochemical depletion. Maximum fractionation was observed at the highest altitude, 34.5 km, where δ15Nαair (isotopomer ratio of center nitrogen), δ15Nβair (end nitrogen), and δ18OSMOW were 144.l‰, 42.4‰, and 119.0‰, respectively. The observed distribution is mostly accounted for by isotopic fractionation during consumption processes, which is in accordance with reported simulation experiments and theoretical prediction for photolytic fractionation of N2O isotopomers. However, the apparent fractionation factors in the lower (

Net CO 2 fluxes between the atmosphere and the ocean, and between the atmosphere and the terrestrial biosphere, were estimated by constraining a two-dimensional atmospheric transport model with the CO 2 concentration and its δ 13 C data obtained from our shipboard measurements in the western Pacific region during the period April 1984 to December 1991. The results obtained for the non-El Nino and Southern Oscillation (ENSO) years during this time period showed that the ocean acted as a CO 2 sink in middle latitudes of both hemispheres and a CO 2 source around the equator. The results also suggested that during the 1984-1991 period there were biospheric CO 2 sources in southern low and northern middle latitudes, and significant biospheric sinks in northern high latitudes. By comparing the latitudinal distributions of CO 2 source/sink for ENSO years with those for non-ENSO years, it was found that a considerable amount of CO 2 was released from the terrestrial biosphere in low latitudes in association with the 1986-1987 ENSO event. While the oceanic region from the equator to 30°N acted as an excess CO 2 sink of about 1.0 Gt C yr -1 during 1987 and 1988, the oceanic contributions to the CO 2 anomaly in the atmosphere were less pronounced in the northern high latitudes and in the southern hemisphere. Also, compared with the estimated interannual fluctuations in the atmosphere-biosphere CO 2 flux, the net CO 2 flux between the atmosphere and the ocean showed relatively less interannual variability.

Sampling for atmospheric isoprene and some other volatile organic compounds was conducted during two cruises in the austral summer, covering the western Pacific, eastern Indian Ocean, Southeast Asian Sea, and Southern Ocean. High isoprene levels were observed in the marine air masses over the southern Indian Ocean (up to 280 parts per trillion by volume (pptv)) and over the Southern Ocean (up to 60 pptv), as well as high levels of dimethyl sulfide and bromoform, both of which are mainly emitted by marine biota. It is highly probable that the high phytoplankton activity in the Southern Ocean during the austral summer was responsible for the high oceanic isoprene levels. The findings suggest a possible significant influence of oceanic isoprene on marine atmospheric chemistry.

Simultaneous balloon-borne in situ measurements of total reactive nitrogen (NO ) and nitrous oxide (N 2 O) were made up to 29 km over Kiruna, Sweden (68°N, 21°E) on February 10 and 25, 1997. Kiruna was located at the edge or inside of the Arctic vortex at potential temperatures between 475 (∼19 km) and 675 K (∼26 km). Below 500 K (∼21 km) the N 2 O values were >120 ppbv on both days, and the observed NO mixing ratios agreed well with those calculated using the NO y -N 2 O correlation previously obtained at northern midlatitudes. An exception was a sharp dip in NO at 445 K (18.4 km) observed on February 25. Back trajectory analyses indicate that this layer had experienced cold temperatures close to ice saturation, i.e., favorable conditions for denitrification. Between 500 and 600 K (∼24 km) the N 2 O values were