Sources of upper tropospheric HO\u3csub\u3e\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3e over the South Pacific Convergence Zone: A case study

A zero‐dimensional (0‐D) model has been applied to study the sources of hydrogen oxide radicals (HOx = HO2 + OH) in the tropical upper troposphere during the Pacific Exploratory Mission in the tropics (PEM‐Tropics B) aircraft mission over the South Pacific in March–April 1999. Observations made across the Southern Pacific Convergence Zone (SPCZ) and the southern branch of the Intertropical Convergence Zone (ITCZ) provided the opportunity to contrast the relative contributions of different sources of HOx, in a nitrogen oxide radical (NOx)‐limited regime, in relatively pristine tropical air. The primary sources of HOx vary significantly along the flight track, in correlation with the supply of water vapor. The latitudinal variation of HOx sources is found to be controlled also by the levels of NOx and primary HOx production rates P(HOx). Budget calculations in the 8‐ to 12‐km altitude range show that the reaction O(1D) + H2O is a major HOx source in the cloud region traversed by the aircraft, including SPCZ and the southern branch of the ITCZ. Production from acetone becomes significant in drier region south of 20°S and can become dominant where water vapor mixing ratios lie under 200 ppmv. Over the SPCZ region, in the cloud outflow, CH3 OOH transported by convection accounts for 22% to 64% of the total primary source. Oxidation of methane amplifies the primary HOx source by 1–1.8 in the dry regions

Global perturbation of stratospheric water and aerosol burden by Hunga eruption

The eruption of the submarine Hunga volcano in January 2022 was associated with a powerful blast that injected volcanic material to altitudes up to 58 km. From a combination of various types of satellite and ground-based observations supported by transport modeling, we show evidence for an unprecedented increase in the global stratospheric water mass by 13% relative to climatological levels, and a 5-fold increase of stratospheric aerosol load, the highest in the last three decades. Owing to the extreme injection altitude, the volcanic plume circumnavigated the Earth in only 1 week and dispersed nearly pole-to-pole in three months. The unique nature and magnitude of the global stratospheric perturbation by the Hunga eruption ranks it among the most remarkable climatic events in the modern observation era, with a range of potential long-lasting repercussions for stratospheric composition and climate

Variabilité de la distribution verticale de l'ozone et des aérosols troposphériques en région méditerranéenne (processus de transport et impacts radiatifs)

Dans le cadre de cette thèse, je me suis intéressé à la variabilité de l ozone et des aérosols troposphériques en région méditerranéenne, plus précisément aux processus de transport qui pilotent cette variabilité et aux impacts radiatifs des aérosols des feux de biomasse. L analyse de la campagne STAAARTE Hellen 96, première campagne aéroportée en Grèce, a permis d établir que la variabilité de l ozone dans cette région est pilotée en premier lieu par le transport à longue distance (Europe occidentale, Afrique du nord et haute troposphère), puis modulée par les émissions locales. Ensuite, l analyse de la campagne Pic 2005, effectuée dans les Pyrénées françaises, a permis de discuter la représentativité de l ozone au niveau de la station d haute altitude du Pic du Midi, plus précisément d estimer l influence exercée par l apport de masses d air issues de la couche limite rurale par les brises orographiques estivales qui se développent dans la journée. A l échelle de quelques heures, on observe souvent en été des écarts de l ordre de 10 ppb entre l ozone mesuré au Pic du Midi et la troposphère libre, écarts qui s expliquent par le transport depuis la couche limite et le mélange de ces masses d air avec la troposphère libre. La mesure en altitude au niveau du Pic du Midi est alors influencée à hauteur de 20 à 50% par la couche limite. Enfin, on a cherché à estimer l impact radiatif des couches d aérosols des feux de biomasse en utilisant d une part les mesures d une campagne d étude du transport intercontinental de la pollution (ITOP 2004), d autre part les observations successives effectuées par CALIPSO des incendies au sud de la Grèce en août 2007.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Analysis and validation of ozone variability observed by lidar during the ESCOMPTE-2001 campaign

An ozone lidar was successfully operated as a ground-based instrument during the ESCOMPTE experiment in June/July 2001. Ozone profiles were measured between 0.5 and 5 km. Moreover, simultaneous measurements of the lidar scattering ratio (SR) at 316 nm diagnosed the diurnal evolution of the PBL top. Comparison of this data set with in-situ measurements by ultralight aircraft (ULM) and balloon soundings supports the existence of well-defined layers over the whole altitude range. Differences between measurements techniques are not due to instrumental inaccuracies but point towards the existence of ozone plumes with sharp horizontal gradients. This is indeed supported by aircraft horizontal cross-section available twice a day at two different levels in the planetary boundary layer (PBL) and the free troposphere. Analysis of the ozone data set has shown a good correlation between surface meteorological conditions, surface ozone measurements and lidar ozone profiles in the PBL. Observed ozone maxima or minima are linked either to sea breeze circulation bringing polluted air masses over the lidar or synoptic flows bringing air with background O3 values into the region. The observed variability of the ozone field is very large over the whole altitude range. Although it is the result of local temporal variability and advection of spatial inhomogenities, the latter proved to be an important contributio

Modélisation à haute résolution du transport de polluants à longue distance

PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Analyse multi-instrumentale de l'influence de la variabilité de la hauteur de couche limite sur la distribution verticale des oxydes d'azote en région parisienne

Les activités humaines et les sources de pollution se concentrent dans les villes, leur donnant un rôle majeur en matière de qualité de l'air et de changement climatique. Quantifier l'impact des émissions urbaines aux échelles régionale à globale nécessite de caractériser l'export des polluants anthropiques urbains. Pendant cette thèse, nous avons étudié la distribution des oxydes d'azote (NOx) en région parisienne, en particulier l'influence de la variabilité de l'épaisseur de la couche limite (CL) sur leur distribution verticale. Pour ce faire, nous avons analysé et comparé les mesures d'instruments déployés au sol et dans l'espace : mesures in-situ de NO2 du réseau AIRPARIF, colonnes intégrées de NO2 du spectromètre UV-visible SAOZ de la station Qualair et des instruments spatiaux SCIAMACHY et GOME, hauteur de CL du microlidar rétrodiffusion de Qualair. La construction de cette base de données a nécessité de nombreux développements algorithmiques, pour déterminer la hauteur de CL à partir des observations lidar ou filtrer les observations du SAOZ en présence de nuages. L'étude combinée de la variabilité de la hauteur de CL et de la distribution des NOx a permis de préciser le lien entre concentration au sol et contenu intégré et a souligné l'intérêt d'une mesure intégrée depuis le sol en centre ville pour estimer les émissions de NOx. Par ailleurs, ce travail a mis en évidence l'existence de forts gradients verticaux de NO2 dans la CL urbaine, l'hypothèse d'un profil vertical uniforme souvent utilisé lors des inversions satellite n'étant pas pertinente. À partir des observations disponibles, nous avons enfin établi, analysé et discuté des conditions de validité d'une relation empirique entre le contenu intégré de NO2 dans la couche limite et sa concentration de surface.Human activities and sources of pollution are concentrated in cities, giving them a major role in air quality and climate change. Quantifying the impact of urban emissions at the regional to global scale requires the characterization of anthropogenic urban pollutants export. During this PhD, we studied the distribution of nitrogen oxides (NOx) in Paris region, with a focus on the influence of boundary layer (BL) depth variability on their vertical distribution. To do this, we analyzed and compared measurements from ground-based and space-borne instruments: in-situ NO2 measurements from the AIRPARIF network, NO2 integrated content from the Qualair station UV-visible spectrometer SAOZ and from the space-borne instruments SCIAMACHY and GOME-2, BL depth from the Qualair backscatter microlidar. Building-up this database required numerous algorithmic developments regarding the determination of BL depth from the lidar observations or the filtration of SAOZ observations in presence of clouds. The combined study of BL depth and NOx distribution variability allowed us to clarify the relationship between ground-level concentration and integrated content, and showed the interest of ground-based and downtown integrated content measurements to estimate the urban emissions of NOx. Furthermore, this work underlined the strong vertical gradients existing in the urban BL, showing that the uniform vertical profile hypothesis often used in satellite inversions is irrelevant. Finally, we used the available observations to establish, analyze and discuss the conditions of validity of an empirical relationship linking the integrated content of NO2 in the BL to its surface concentration.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

QualAir atmospheric measurement at University Pierre et Marie Curie, Paris

International audienceQualAir is a joint remote-sensing observation platform from LATMOS and LPMAA, located in Paris city centre. It addresses the need for information about pollutant vertical distributions to improve our understanding of pollution peak processes and assess ground-based air quality measurements representativity. Moreover, it offers possibilities for satellite validation over urban areas.The station measures integrated columns of NO2 (SAOZ UV-visible zenith-skyspectrometer), atmospheric pollutants (infrared Fourier transform spectrometer) and aerosols (AERONET sun photometer). An elastic backscatter lidar provides aerosol extinction profiles and observations of boundary layer (BL) height variability.Here, BL depth is determined from lidar data on an hourly basis. BL top is defined as the altitude of minimal signal gradient or as the cloud base, if a cloud is capping the BL. The same treatment is applied to SIRTA lidar data to show regional variability of BL depth. Results are presented in Figure 2 for both MEGAPOLI campaigns, together with ECMWF forecasts. In summer during daytime, the effect of solar radiation and convection is predominant and there is no noticable difference between Paris centre and suburbs. In winter, as the solar flux is lower, BL depth over the city tends to be higher due to the heat island effect. ECMWF forecasts agree reasonably well to observations given their low temporal resolution.The very high resolution Fourier transform spectrometer of the LPMAA records the infrared solar spectra from QualAir roof. The spectral region (3.1-5.1μm) is selected to monitor atmospheric pollutants like CO, CO2, N2O, O3, H2O, CH4, HCl, HF. The spectral signature of those gases allows to retrieve their abundances in the atmosphere using a radiative transfer algorithm. Figure 3 shows the P(8) CO absorption line (located at 2111.543 cm-1) that is used to determine the CO concentration vertical profile for July 1st 2009 (Figure 4). Fluctuating signals around 35500 s are due to the thin clouds presence. The CO volume mixing ratio obtained by the FTIR at ground level (on average, 0.31 ± 0.05 ppmv) compared well to the CO in-situ measurements from QualAir CO11M analyzer (on average, 0.27 ± 0.10 ppmv)

SLM_Polar

Modified simplifid versions, recoded in Python, of the Noah Land Surface Model used in conjunction with the Mellor-Janjic-Yamada surface layer scheme (Noah MYJ) and the Noah MultiPhysics scheme (Noah-MP) from the WRF 4.5.1 meso-scale model. Modifications are used to correct the fact that original WRF schemes place strong limits on the turbulent collapse, leading to lower surface temperature gradient at low wind speeds. Modified versions show a better performance in reproducing positive temperature gradients over forested areas in the Arctic winter. Noah-MP is found to perform better than Noah-LSM–MYJ because the former is a 2-layer model which explicitly takes into account the effect of the forest canopy. Indeed a non-negligible temperature gradient is maintained below the canopy at high wind speeds, leading to overall larger gradients than in the absence of vegetation

Evaluation and development of surface layer scheme representation of temperature inversions over boreal forests in Arctic wintertime conditions

International audienceIn this study, the Noah land surface model used in conjunction with the Mellor–Yamada–Janjic ́ surface layer scheme (hereafter, Noah-MYJ) and the Noah multiphysics scheme (Noah-MP) from the Weather Research and Fore- casting (WRF) 4.5.1 mesoscale model are evaluated with re- gard to their performance in reproducing positive tempera- ture gradients over forested areas in the Arctic winter. First, simplified versions of the WRF schemes, recoded in Python, are compared with conceptual models of the surface layer in order to gain insight into the dependence of the temper- ature gradient on the wind speed at the top of the surface laye