A portable infrared laser spectrometer for flux measurements of trace gases at the geosphere-atmosphere interface

International audienceA portable infrared laser absorption spectrometer named SPIRIT (SPectrom'etre Infra-Rouge In situ Troposph'erique) has been set up for the simultaneous flux measurements of trace gases at the geosphere-atmosphere interface. It uses a continuous wave distributed feedback room temperature quantum cascade laser and a patented new optical multi-pass cell. The aim of SPIRIT field studies is to get a better understanding of land and water bodies to atmosphere exchange mechanisms of greenhouse gases (GHG). The analytical procedures to derive concentrations and fluxes are described, as well as the performances of the instrument under field conditions. The ability of SPIRIT to assess space and time dependence emissions of two GHG--nitrous oxide (N2O) and methane (CH4)--for different types of ecosystems is demonstrated through in situ measurements on peatland, on fertilized soil, and on water body systems. The objectives of these investigations and preliminary significant results are reported

Pattern and Outcome of Chest Injuries at Bugando Medical Centre in Northwestern Tanzania.

Chest injuries constitute a continuing challenge to the trauma or general surgeon practicing in developing countries. This study was conducted to outline the etiological spectrum, injury patterns and short term outcome of these injuries in our setting. This was a prospective study involving chest injury patients admitted to Bugando Medical Centre over a six-month period from November 2009 to April 2010 inclusive. A total of 150 chest injury patients were studied. Males outnumbered females by a ratio of 3.8:1. Their ages ranged from 1 to 80 years (mean = 32.17 years). The majority of patients (72.7%) sustained blunt injuries. Road traffic crush was the most common cause of injuries affecting 50.7% of patients. Chest wall wounds, hemothorax and rib fractures were the most common type of injuries accounting for 30.0%, 21.3% and 20.7% respectively. Associated injuries were noted in 56.0% of patients and head/neck (33.3%) and musculoskeletal regions (26.7%) were commonly affected. The majority of patients (55.3%) were treated successfully with non-operative approach. Underwater seal drainage was performed in 39 patients (19.3%). One patient (0.7%) underwent thoracotomy due to hemopericardium. Thirty nine patients (26.0%) had complications of which wound sepsis (14.7%) and complications of long bone fractures (12.0%) were the most common complications. The mean LOS was 13.17 days and mortality rate was 3.3%. Using multivariate logistic regression analysis, associated injuries, the type of injury, trauma scores (ISS, RTS and PTS) were found to be significant predictors of the LOS (P < 0.001), whereas mortality was significantly associated with pre-morbid illness, associated injuries, trauma scores (ISS, RTS and PTS), the need for ICU admission and the presence of complications (P < 0.001). Chest injuries resulting from RTCs remain a major public health problem in this part of Tanzania. Urgent preventive measures targeting at reducing the occurrence of RTCs is necessary to reduce the incidence of chest injuries in this region

Reformulation of the strong-field approximation for light-matter interactions

We consider the interaction of hydrogen-like atoms with a strong laser field and show that the strong field approximation and all its variants may be grouped into a set of families of approximation schemes. This is done by introducing an ansatz describing the electron wave packet as the sum of the initial state wave function times a phase factor and a function which is the perturbative solution in the Coulomb potential of an inhomogeneous time-dependent Schr\"odinger equation. It is the phase factor that characterizes a given family. In each of these families, the velocity and length gauge version of the approximation scheme lead to the same results at each order in the Coulomb potential. By contrast, irrespective of the gauge, approximation schemes belonging to different families give different results. Furthermore, this new formulation of the strong field approximations allows us to gain deeper insight into the validity of the strong field approximation schemes. In particular, we address two important questions: the role of the Coulomb potential in the output channel and the convergence of the perturbative series in the Coulomb potential. In all the physical situations we consider here, our results are compared to those obtained by solving numerically the time-dependent Schr\"odinger equation.Comment: 19 pages, 9 figures, submitted for publicatio

Aerosol influences on low-level clouds in the West African monsoon

Low-level clouds (LLC) cover a wide area of southern West Africa (SWA) during the summer monsoon months, and have an important cooling effect on the regional climate. Previous studies of these clouds have focused on modelling and remote sensing via satellite. We present the first comprehensive set of regional, in situ measurements of cloud microphysics, taken during June – July 2016, as part of the DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa) campaign, assessing spatial and temporal variation in the properties of these clouds. LLC developed overnight and mean cloud cover peaked a few hundred kilometres inland around 10:00 local solar time (LST), before clouds began to dissipate and convection intensified in the afternoon. Additional sea breeze clouds developed near the coast in the late morning, reaching a maximum extent around 12:00 LST. Regional variation in LLC cover was largely determined by the modulation of the cool maritime inflow by the local orography, with peaks on the upwind side of hills and minima on the leeward sides. In the broad-scale cloud field, no lasting impacts related to anthropogenic aerosol were observed downwind of major population centres. The boundary layer cloud drop number concentration (CDNC) was locally variable inland, ranging from 200 to 840 cm−3 (10th and 90th percentiles at standard temperature and pressure), but showed no systematic regional variations. Enhancements were seen in pollution plumes from the coastal cities, but were not statistically significant across the region. The majority of accumulation mode aerosols, and therefore cloud condensation nuclei, were from ubiquitous biomass burning smoke transported from the southern hemisphere. Consequently, all clouds measured (inland and offshore) had significantly higher CDNC and lower effective radius than clouds over the remote south Atlantic from literature. A parcel model sensitivity analysis showed that doubling or halving local emissions only changed the calculated CDNC by 13–22 %, as the high background meant local emissions were a small fraction of total aerosol. As the population of SWA grows, local emissions are expected to rise. Biomass burning smoke transported from the southern hemisphere is likely to dampen any effect of these increased local emissions on cloud-aerosol interactions. An integrative analysis between local pollution and Central African biomass burning emissions must be considered when predicting anthropogenic impacts on the regional cloud field during the West African monsoon

Modelling the chemistry and transport of bromoform within a sea breeze driven convective system during the SHIVA Campaign

We carry out a case study of the transport and chemistry of bromoform and its product gases (PGs) in a sea breeze driven convective episode on 19 November 2011 along the North West coast of Borneo during the "Stratospheric ozone: Halogen Impacts in a Varying Atmosphere" (SHIVA) campaign. We use ground based, ship, aircraft and balloon sonde observations made during the campaign, and a 3-D regional online transport and chemistry model capable of resolving clouds and convection explicitly that includes detailed bromine chemistry. The model simulates the temperature, wind speed, wind direction fairly well for the most part, and adequately captures the convection location, timing, and intensity. The simulated transport of bromoform from the boundary layer up to 12 km compares well to aircraft observations to support our conclusions. The model makes several predictions regarding bromine transport from the boundary layer to the level of convective detrainment (11 to 12 km). First, the majority of bromine undergoes this transport as bromoform. Second, insoluble organic bromine carbonyl species are transported to between 11 and 12 km, but only form a small proportion of the transported bromine. Third, soluble bromine species, which include bromine organic peroxides, hydrobromic acid (HBr), and hypobromous acid (HOBr), are washed out efficiently within the core of the convective column. Fourth, insoluble inorganic bromine species (principally Br2) are not washed out of the convective column, but are also not transported to the altitude of detrainment in large quantities. We expect that Br2 will make a larger relative contribution to the total vertical transport of bromine atoms in scenarios with higher CHBr3 mixing ratios in the boundary layer, which have been observed in other regions. Finally, given the highly detailed description of the chemistry, transport and washout of bromine compounds within our simulations, we make a series of recommendations about the physical and chemical processes that should be represented in 3-D chemical transport models (CTMs) and chemistry climate models (CCMs), which are the primary theoretical means of estimating the contribution made by CHBr3 and other very short-lived substances (VSLS) to the stratospheric bromine budget

N2_2O Temporal Variability from the Middle Troposphere to the Middle Stratosphere Based on Airborne and Balloon-Borne Observations during the Period 1987–2018

Nitrous oxide (N$_2$O) is the fourth most important greenhouse gas in the atmosphere and is considered the most important current source gas emission for global stratospheric ozone depletion (O$_3$). It has natural and anthropogenic sources, mainly as an unintended by-product of food production activities. This work examines the identification and quantification of trends in the N$_2$O concentration from the middle troposphere to the middle stratosphere (MTMS) by in situ and remote sensing observations. The temporal variability of N$_2$O is addressed using a comprehensive dataset of in situ and remote sensing N$_2$O concentrations based on aircraft and balloon measurements in the MTMS from 1987 to 2018. We determine N$_2$O trends in the MTMS, based on observations. This consistent dataset was also used to study the N$_2$O seasonal cycle to investigate the relationship between abundances and its emission sources through zonal means. The results show a long-term increase in global N$_2$O concentration in the MTMS with an average of 0.89 ± 0.07 ppb/yr in the troposphere and 0.96 ± 0.15 ppb/yr in the stratosphere, consistent with 0.80 ppb/yr derived from ground-based measurements and 0.799 ± 0.024 ppb/yr ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) satellite measurements