Ozone et propriétés oxydantes de la troposphère

Le présent article traite de l'augmentation des concentrations en ozone et en photo-oxydants observée dans la troposphère, partie inférieure de l'atmosphère comprise entre le sol et une altitude d'environ 15 km. Ce problème sérieux d'environnement planétaire est resté jusqu'aujourd'hui moins connu que celui de l'effet de serre ou de la diminution de l'ozone dans la stratosphère. Cela est largement dû à la variabilité spatiotemporelle et à la complexité des très nombreux mécanismes physicochimiques et atmosphériques mis en jeu . À nos latitudes, la teneur moyenne en ozone dans l'air a quadruplé depuis le début du siècle. Dans les régions polluées, cette teneur dépasse fréquemment les normes recommandées. Cette augmentation des concentrations en ozone dans la basse atmosphère reflète directement l'impact des émissions anthropiques de constituants comme le méthane, le monoxyde de carbone, les hydrocarbures et les oxydes d'azote, qui, par l'intermédiaire de réactions chimiques complexes, conduisent, en présence de rayonnement solaire, à la formation d'ozone. Les conséquences de cette modification des propriétés oxydantes de la troposphère commencent à se faire sentir, tant sur la production végétale que sur la santé humaine et sur les équilibres climatiques.This article is about the rising concentrations of ozone and photooxidizers observed in the troposphère, the atmosphère between the ground and a height of 10 to 15 km. This serious global environmental problem has up to now been less well known than the greenhouse effect or the decrease in stratospheric ozone. This is because it varies with time and place and involves many complicated physico-chemical and atmospheric processes. At our latitudes, the average ozone concentration in the air we breathe has quadrupled since the beginning of this century. In polluted areas it often exceeds the recommended norms. This increase in ozone concentrations in the lower atmosphère directly reflects the impact of man-made émissions of compounds like méthane, carbon monoxide, hydrocarbons and nitrogen oxides. Sunlight acts on thèse compounds to form ozone via complicated chemical reactions. This change in oxidizing properties of the troposphère is beginning produce perceptible effects on vegetable production, human health and climate

Lidar measurements of ozone vertical profiles

International audienceAttention is given to the differential absorption lidar technique used in measuring the vertical ozone distribution of the troposphere and stratosphere. The basis of these measurements are UV wavelength range laser sources which encompass Nd:YAG pumped dye lasers and Exciplex lasers. High temporal and spatial resolution, together with measurement continuity, allow the observation of ozone variations at various time and space scales that are important in such areas of current interest as troposphere-stratosphere exchanges, long range transport, the global ozone budget, and correlations between ozone number densities and other atmospheric parameters

Ozone vertical distribution and total content using a ground-based active remote sensing technique

International audienceThe evaluation of possible perturbations of anthropogenic origin on the Earth environment has become increasingly important with the development of industrial and agricultural activities. Among these the depletion of the ozone layer under the influence of chemically active minor constituents produced by anthropogenic sources is still under question, thus emphasizing the importance of ozone monitoring in the atmosphere. Beside classical systems, such as the Dobson spectrometer and Brewer or ECC sondes, new techniques of ozone monitoring are being developed which include passive IR and microwave spectrometry and active IR and UV laser soundings1. They should soon allow complementary routine measurements. We have previously described2 the UV lidar system set up at the Observatoire de Haute Provence (44° N, 6° E) in the south of France and the methodology of the differential absorption laser technique (DIAL) which provide routine measurements of the ozone vertical distribution from the ground up to 25 km. We report here the first active ground-based measurements of the ozone distribution at higher altitudes up to 40 km and of the total ozone content using the same system

In situ measurements of H₂O from a stratospheric balloon by diode laser direct-differential absorption spectroscopy at 1.39 µm

International audienceA distributed-feedback InGaAs laser diode emitting near 1.393 µm is used in conjunction with an optical multipass cell that is open to the atmosphere to yield ambient water-vapor measurements by infrared absorption spectroscopy. To obtain the high dynamic range for the measurements that is required for continuous water-vapor monitoring in the upper troposphere and the lower stratosphere, we used a simple circuit that combined differential and direct detection. Furthermore, the laser emission wavelength was tuned to balance the steep decrease in H2O concentration with altitude by sweeping molecular transitions of stronger line strengths. The technique was implemented by use of the Spectromètre à Diodes Laser Accordables (SDLA), a tunable diode laser spectrometer operated from a stratospheric balloon. Absorption spectra of H2O in the 5–30-km altitude range obtained at 1-s intervals during recent balloon flights are reported. Water-vapor mixing ratios were retrieved from the absorption spectra by a fit to the full molecular line shape in conjunction with in situ pressure and temperature measurements, with a precision error ranging from 5% to 10%

Daytime lidar measurements of the mesospheric ozone layer

International audienceDaytime lidar measurements of the mesospheric sodium layer have been performed at the Haute Provence Observatory from 1979 to 1981. High values of the signal to noise ratio (> 50) are obtained by simultaneously reducing the receiver bandwidth down to 20 pm and its field of view to 3.10 -4 radian. The long term behaviour of the sodium layer during daytime is similar to the one already observed for nighttime by previous lidar soundings. No regular variation of the characteristics parameters of the sodium layer-total content, altitude of the concentration maximum, topside and bottom side scale heights-during the diurnal cycle or during day-night transitions have been observed, suggesting that the photochemical processes are not dominant in governing the behaviour of the upper atmospheric sodium atoms