The hydrogen isotopic composition of water vapor entering the stratosphere inferred from high-precision measurements of δD-CH_4 and δD-H_2

The hydrogen isotopic composition of water vapor entering the stratosphere provides an important constraint on the mechanisms for dehydration of air ascending through the tropical tropopause layer. We have inferred the annual mean hydrogen isotopic composition of water vapor entering the stratosphere (or δD-H_(2)O_0) for the mid to late 1990s based on high-precision measurements of the hydrogen isotopic compositions of stratospheric H_2 and CH_4 from whole air samples collected on the NASA ER-2 aircraft between 1996 and 2000 and remote observations of δD-H_2O from the FIRS-2 far infrared spectrometer. We calculate an annual mean value for δD-H_(2)O_0 of −653 (+24/−25)‰ relative to Vienna standard mean ocean water (VSMOW). Previous inferences from balloon-borne and spacecraft remote-sensing observations are ∼20‰ lighter than the value from this analysis. We attribute the difference to an underestimation of deuterium in the molecular H_2 reservoir in earlier work. This precise and more accurate value for the annual mean δD-H_(2)O_0 will be useful as a 1990's benchmark for detecting future changes in the details of the dehydration of air due to the impact of climate change on convection intensity, cloud microphysics, or tropical tropopause layer temperatures. In addition, we report a value for the total deuterium content in the three main stratospheric hydrogen reservoirs HDO, HD, and CH_(3)D of 1.60 (+0.02/−0.03) ppbv

The distribution of hydrogen, nitrogen, and chlorine radicals in the lower stratosphere: Implications for changes in O_3 due to emission of NO_y from supersonic aircraft

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained in the lower stratosphere during SPADE are compared to results from a photochemical model that assimilates measurements of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N_2O_5 agree well with measured concentrations of NO and ClO, but concentrations of HO_2 and OH are underestimated by 10 to 25%, concentrations of NO_2 are overestimated by 10 to 30%, and concentrations of HCl are overestimated by a factor of 2. Discrepancies for [OH] and [HO_2] are reduced if we allow for higher yields of O(^1D) from O_3 photolysis and for heterogeneous production of HNO_2. The data suggest more efficient catalytic removal of O_3 by hydrogen and halogen radicals relative to nitrogen oxide radicals than predicted by models using recommended rates and cross sections. Increases in [O_3] in the lower stratosphere may be larger in response to inputs of NO_y from supersonic aircraft than estimated by current assessment models

The diurnal variation of hydrogen, nitrogen, and chlorine radicals: implications for the heterogeneous production of HNO_2

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N_(2)O_(5) on sulfate aerosols agree with measured concentrations of NO, NO_(2), and ClO throughout the day, but fail to account for high concentrations of OH and HO_(2) observed near sunrise and sunset. The morning burst of [OH] and [HO_(2)] coincides with the rise of [NO] from photolysis of NO_(2), suggesting a new source of HO_(x) that photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HNO_(2) results in an excellent simulation of the diurnal variations of [OH] and [HO_(2)]

Comparison between DC-8 and ER-2 species measurements in the tropical middle troposphere: NO, NO\u3csub\u3ey\u3c/sub\u3e, O\u3csub\u3e3\u3c/sub\u3e, CO\u3csub\u3e2\u3c/sub\u3e, CH\u3csub\u3e4\u3c/sub\u3e, and N\u3csub\u3e2\u3c/sub\u3eO

We compare measurements of six species taken aboard NASA DC-8 and ER-2 aircraft during two flight legs in the tropical middle troposphere near Hawaii. NO, NOy, O3, CH4, and N2O measurements agree to within the limits set by the known systematic errors. For CO2, which can be measured with better relative precision than the other five species, differences in measured values from the two platforms are slightly larger than expected if the air masses sampled by the two aircraft were indeed similar in CO2 composition to better than 0.08%. Copyright 1998 by the American Geophysical Union

Observations of the anomalous oxygen isotopic composition of carbon dioxide in the lower stratosphere and the flux of the anomaly to the troposphere

Measurements of the triple oxygen isotopic composition of stratospheric CO2 in whole air samples from the NASA ER‐2 aircraft show anomalous enrichments in 17O and 18O. The compact correlation of the isotope anomaly (defined as Δ17O = δ17O − 0.516 × δ18O) with simultaneous N2O measurements demonstrates that Δ17OCO2 is a long‐lived tracer with a stratospheric source. These characteristics, and an isotopic link to O3 production, make Δ17OCO2 potentially useful as a tracer of integrated stratospheric chemistry and transport. The Δ17OCO2:N2O correlation is also used to estimate a net Δ17OCO2 flux to the troposphere of 3.6 ± 0.9 × 1015‰ mol CO2 yr−1. This flux is required to predict and understand the CO2 and O2 isotope anomalies in the troposphere and their use as tracers of gross carbon exchanges between the atmosphere and biosphere on interannual to glacial‐interglacial time scales