Measurement of low-ppm mixing ratios of water vapor in the upper troposphere and lower stratosphere using chemical ionization mass spectrometry

Abstract. A chemical ionization mass spectrometer (CIMS) instrument has been developed for the fast, precise, and accurate measurement of water vapor (H2O) at low mixing ratios in the upper troposphere and lower stratosphere (UT/LS). A low-pressure flow of sample air passes through an ionization volume containing an α-particle radiation source, resulting in a cascade of ion-molecule reactions that produce hydronium ions (H3O+) from ambient H2O. The production of H3O+ ions from ambient H2O depends on pressure and flow through the ion source, which were tightly controlled in order to maintain the measurement sensitivity independent of changes in the airborne sampling environment. The instrument was calibrated every 45 min in flight by introducing a series of H2O mixing ratios between 0.5 and 153 parts per million (ppm, 10−6 mol mol−1) generated by Pt-catalyzed oxidation of H2 standards while overflowing the inlet with dry synthetic air. The CIMS H2O instrument was deployed in an unpressurized payload area aboard the NASA WB-57F high-altitude research aircraft during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) mission in March and April 2011. The instrument performed successfully during seven flights, measuring H2O mixing ratios below 5 ppm in the lower stratosphere at altitudes up to 17.7 km, and as low as 3.5 ppm near the tropopause. Data were acquired at 10 Hz and reported as 1 s averages. In-flight calibrations demonstrated a typical sensitivity of 2000 Hz ppm−1 at 3 ppm with a signal to noise ratio (2 σ, 1 s) greater than 32. The total measurement uncertainty was 9 to 11%, derived from the uncertainty in the in situ calibrations.

[1]  Nasa.  Nitric Acid Uptake on Subtropical Cirrus Cloud Particles , 2013 .

[2]  S. J. Ciciora,et al.  A compact, fast UV photometer for measurement of ozone from research aircraft , 2012 .

[3]  Thierry Leblanc,et al.  Ground-based water vapor raman lidar measurements up to the upper troposphere and lower stratosphere for long-term monitoring , 2012 .

[4]  D. Fahey,et al.  Catalytic oxidation of H 2 on platinum: a robust method for generating low mixing ratio H 2 O standards , 2011 .

[5]  A. Maycock,et al.  The temperature response to stratospheric water vapour changes , 2011 .

[6]  S. Solomon,et al.  Contributions of Stratospheric Water Vapor to Decadal Changes in the Rate of Global Warming , 2010, Science.

[7]  D. S. Sayres,et al.  Validation of the Harvard Lyman‐α in situ water vapor instrument: Implications for the mechanisms that control stratospheric water vapor , 2009 .

[8]  G. Brasseur,et al.  Aeronomy of the Middle Atmosphere , 2009 .

[9]  A. Mangold,et al.  Ice supersaturations and cirrus cloud crystal numbers , 2008 .

[10]  G. Stiller,et al.  First airborne water vapor lidar measurements in the tropical upper troposphere and mid-latitudes lower stratosphere: accuracy evaluation and intercomparisons with other instruments , 2008 .

[11]  D. S. Sayres,et al.  Formation of large (≃100 μm) ice crystals near the tropical tropopause , 2007 .

[12]  H. Vömel,et al.  Accuracy of tropospheric and stratospheric water vapor measurements by the cryogenic frost point hygrometer: Instrumental details and observations , 2007 .

[13]  S. Menhart,et al.  Residence times of water molecules on stainless steel and aluminum surfaces in vacuum and atmosphere , 2007 .

[14]  L. G. Huey.  Measurement of trace atmospheric species by chemical ionization mass spectrometry: speciation of reactive nitrogen and future directions. , 2007, Mass spectrometry reviews.

[15]  K. Trenberth,et al.  Observations: Surface and Atmospheric Climate Change , 2007 .

[16]  Peter Spichtinger,et al.  When Dry Air Is Too Humid , 2006, Science.

[17]  Manuel López-Puertas,et al.  Water vapor distributions measured with the Michelson Interferometer for Passive Atmospheric Sounding on board Envisat (MIPAS/Envisat) , 2005 .

[18]  Ann M. Fridlind,et al.  Ice supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration , 2004 .

[19]  V. Anicich.  An index of the literature for bimolecular gas phase cation-molecule reaction kinetics , 2003 .

[20]  P. Forster,et al.  Assessing the climate impact of trends in stratospheric water vapor , 2002 .

[21]  William G. Read,et al.  UARS Microwave Limb Sounder upper tropospheric humidity measurement: Method and validation , 2001 .

[22]  T. L. Thompson,et al.  A fast-response chemical ionization mass spectrometer for in situ measurements of HNO3 in the upper troposphere and lower stratosphere , 2000 .

[23]  James M. Russell,et al.  SPARC assessment of upper tropospheric and stratospheric water vapour , 2000 .

[24]  D. Fahey,et al.  Computer-controlled Teflon flow control valve , 1999 .

[25]  R. May,et al.  On the accuracy of in situ water vapor measurements in the troposphere and lower stratosphere with the Harvard Lyman‐α hygrometer , 1999 .

[26]  D. McKenna,et al.  Fast in situ stratospheric hygrometers: A new family of balloon‐borne and airborne Lyman α photofragment fluorescence hygrometers , 1999 .

[27]  Randy D. May,et al.  Open‐path, near‐infrared tunable diode laser spectrometer for atmospheric measurements of H2O , 1998 .

[28]  E. Weinstock,et al.  New fast response photofragment fluorescence hygrometer for use on the NASA ER‐2 and the Perseus remotely piloted aircraft , 1994 .

[29]  H. Dylla,et al.  Model for water outgassing from metal surfaces. II , 1994 .

[30]  Guy Brasseur,et al.  Aeronomy of the Middle Atmosphere: Chemistry and Physics of the Stratosphere and Mesosphere , 1984 .

[31]  E. Ferguson.  Laboratory measurements of ionospheric ion‐molecule reaction rates , 1974 .

[32]  M. Takebe.  Positive Ion Species and Their Mobilities in Air , 1974 .

[33]  F. Fehsenfeld,et al.  Ion—Molecule Reactions in an O2+–H2O System , 1971 .