Tropospheric H(2) budget and the response of its soil uptake under the changing environment

Molecular hydrogen (H(2)) is an indirect greenhouse gas present at the trace level in the atmosphere. So far, the sum of its sources and sinks is close to equilibrium, but its large-scale utilization as an alternative energy carrier would alter its atmospheric burden. The magnitude of the emissions associated with a future H(2)-based economy is difficult to predict and remains a matter of debate. Previous attempts to predict the impact that a future H(2)-based economy would exert on tropospheric chemistry were realized by considering a steady rate of microbial-mediated soil uptake, which is currently responsible of ~80% of the tropospheric H(2) losses. Although soil uptake, also known as dry deposition is the most important sink for tropospheric H(2), microorganisms involved in the activity remain elusive. Given that microbial-mediated H(2) soil uptake is influenced by several environmental factors, global change should exert a significant effect on the activity and then, assuming a steady H(2) soil uptake rate for the future may be mistaken. Here, we present an overview of tropospheric H(2) sources and sinks with an emphasis on microbial-mediated soil uptake process. Future researches are proposed to investigate the influence that global change would exert on H(2) dry deposition and to identify microorganisms involved H(2) soil uptake activity.

Lightweight diode laser spectrometer CHILD (Compact High-altitude iN-situ Laser Diode) for balloonborne measurements of water vapor and methane

A new lightweight near-infrared tunable diode laser spectrometer CHILD (Compact High-altitude In-situ Laser Diode spectrometer) was developed for flights to the stratosphere as an additional in situ sensor on existing balloonborne payloads. Free-air absorption measurements in the near infrared are made with an open-path Herriott cell with new design features. It offers two individual absorption path lengths optimized for CH4 with 74 m (136 pass) and H2O with 36 m (66 pass). New electronic features include a real-time gain control loop that provides an autocalibration function. In flight-ready configuration the instrument mass is approximately 20 kg, including batteries. It successfully measured stratospheric CH4 and H2O profiles on high-altitude balloons on four balloon campaigns (Environmental Satellite validation) between October 2001 and June 2003. On these first flights, in situ spectra were recorded from ground level to 32,000-m altitude with a sensitivity of 0.1 ppm [(parts per million), ground] to 0.4 ppm (32,000 m) for methane and 0.15-0.5 ppm for water.

In situ sensing of the middle atmosphere with balloonborne near-infrared laser diodes

Since 1997, two near-infrared laser diode sensors have been developed with the support of the CNES, the French space agency, to provide in situ data of H(2)O, CH(4) and CO(2) in the middle atmosphere. The realized instruments were flown from stratospheric balloons within the framework of European campaigns for the study of stratospheric ozone and water vapor and were involved in the validation of the ODIN and ENVISAT satellites. In this paper, we describe the developed laser probing technique, we report atmospheric measurements and finally we discuss future perspectives, particularly the in situ laser sensing of the lower atmosphere of Mars and the implication of the laser hygrometers in balloon campaigns at mid-latitudes and tropical regions to investigate the sources and sinks of stratospheric H(2)O.