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International audience

International audience

International audience

Objective: Intrahospital Transport (IT) of critically ill patients, is a routine occurence. IT increases the risk of complications. The patient collective of a neuro-intensive care unit differentiates itself from that of other critical care units, amongst many other factors, by the higher number of [for full text, please go to the a.m. URL], 65. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC)

Objective: Percutaneous tracheotomy is a relatively common procedure on critical care units worldwide. A reversible periprocedural ICP-increase above the widely considered upper limit of 20mmHg is often observed in patients with acute cerebral diseases. It is unclear, which factors determine this ICP-increase.[for full text, please go to the a.m. URL], 65. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC)

Objective: Bedside percutaneous tracheotomy (PT) is very common for critical ill patients, who require prolonged mechanical ventilation. The effect of the tracheotomy on the intracranial pressure (ICP) is currently subject of debate. Studies with differing results have been published. The aim of our[for full text, please go to the a.m. URL], 63. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC), Joint Meeting mit der Japanischen Gesellschaft für Neurochirurgie (JNS)

Tropospheric ozone (O3) is a known greenhouse gas responsible for impacts on human and animal health and ecosystem functioning. In addition, O3 plays an important role in tropospheric chemistry, together with nitrogen oxides. The determination of surface-atmosphere exchange fluxes of these trace gases is a prerequisite to establish their atmospheric budget and evaluate their impact onto the biosphere. In this study, O3, nitric oxide (NO) and nitrogen dioxide (NO2) fluxes were measured using the aerodynamic gradient method over a bare soil in an agricultural field. Ozone and NO fluxes were also measured using eddy-covariance and automatic chambers, respectively. The aerodynamic gradient measurement system, composed of fast response sensors, was capable to measure significant differences in NO and O3 mixing ratios between heights. However, due to local advection, NO2 mixing ratios were highly non-stationary and NO2 fluxes were, therefore, not significantly different from zero. The chemical reactions between O3, NO and NO2 led to little ozone flux divergence between the surface and the measurement height (less than 1% of the flux on average), whereas the NO flux divergence was about 10% on average. The use of fast response sensors allowed reducing the flux uncertainty. The aerodynamic gradient and the eddy-covariance methods gave comparable O3 fluxes. The chamber NO fluxes were down to 70% lower than the aerodynamic gradient fluxes, probably because of either the spatial heterogeneity of the soil NO emissions or the perturbation due to the chamber itself.

Recent studies have shown that measured OH under NOx-limited, high-isoprene conditions are many times higher than modeled OH. In this study, a detailed analysis of the HOx radical budgets under low-NOx, rural conditions was performed employing a box model based on the Master Chemical Mechanism (MCMv3.2). The model results were compared with HOx radical measurements performed during the international HOxComp campaign carried out in Julich, Germany, during summer 2005. Two different air masses influenced the measurement site denoted as high-NOx (NO, 1-3 ppbv) and low-NOx (NO, < 1 ppbv) periods. Both modeled OH and HO2 diurnal profiles lay within the measurement range of all HOx measurement techniques, with correlation slopes between measured and modeled OH and HO2 around unity. Recently discovered interference in HO2 measurements caused by RO2 cross sensitivity was found to cause a 30% increase in measured HO2 during daytime on average. After correction of the measured HO2 data, the model HO2 is still in good agreement with the observations at high NOx but overpredicts HO2 by a factor of 1.3 to 1.8 at low NOx. In addition, for two different set of measurements, a missing OH source of 3.6 +/- 1.6 and 4.9 +/- 2.2 ppb h(-1) was estimated from the experimental OH budget during the low-NOx period using the corrected HO2 data. The measured diurnal profile of the HO2/OH ratio, calculated using the corrected HO2, is well reproduced by the MCM at high NOx but is significantly overestimated at low NOx. Thus, the cycling between OH and HO2 is better described by the model at high NOx than at low NOx. Therefore, similar comprehensive field measurements accompanied by model studies are urgently needed to investigate HOx recycling under low-NOx conditions.

International audience; Tropospheric ozone (O 3) is a known greenhouse gas responsible for impacts on human and animal health and ecosystem functioning. In addition, O 3 plays an important role in tropospheric chemistry, together with nitrogen oxides. The determination of surface-atmosphere exchange fluxes of these trace gases is a prerequisite to establish their atmospheric budget and evaluate their impact onto the biosphere. In this study, O 3 , nitric oxide (NO) and nitrogen dioxide (NO 2) fluxes were measured using the aerodynamic gradient method over a bare soil in an agricultural field. Ozone and NO fluxes were also measured using eddy-covariance and automatic chambers, respectively. The aerodynamic gradient measurement system, composed of fast response sensors , was capable to measure significant differences in NO and O 3 mixing ratios between heights. However, due to local advection, NO 2 mixing ratios were highly non-stationary and NO 2 fluxes were, therefore, not significantly different from zero. The chemical reactions between O 3 , NO and NO 2 led to little ozone flux divergence between the surface and the measurement height (less than 1 % of the flux on average), whereas the NO flux divergence was about 10 % on average. The use of fast response sensors allowed reducing the flux uncertainty. The aerodynamic gradient and the eddy-covariance methods gave comparable O 3 fluxes. The chamber NO fluxes were down to 70 % lower than the aerodynamic gradient fluxes, probably because of either the spatial heterogeneity of the soil NO emissions or the perturbation due to the chamber itself.

Measurements of gaseous nitrogen and sulfur oxide emissions in young aircraft exhaust plumes give insight into chemical oxidation processes inside aircraft engines. Particularly, the OHâ��induced formation of nitrous acid (HONO) from nitrogen oxide (NO) and sulfuric acid (H2SO4) from sulfur dioxide (SO2) inside the turbine which is highly uncertain, need detailed analysis to address the climate impact of aviation. We report on airborne in situ measurements at cruise altitudes of HONO, NO, NOy, and SO2 in 9 wakes of 8 different types of modern jet airliners, including for the first time also an A380. Measurements of HONO and SO2 were made with an ITCIMS (Ion Trap Chemical Ionization Mass Spectrometer) using a new ionâ��reaction scheme involving SF5 â�� reagent ions. The measured molar ratios HONO/NO and HONO/NOy with averages of 0.038 �± 0.010 and 0.027 �± 0.005 were found to decrease systematically with increasing NOx emissionâ��index (EI NOx). We calculate an average EI HONO of 0.31 �± 0.12 g NO2 kgâ��1. Using reliable measurements of HONO and NOy, which are less adhesive than H2SO4 to the inlet walls, we derive the OHâ��induced conversion fraction of fuel sulfur to sulfuric acid " with an average of 2.2 �± 0.5 %. " also tends to decrease with increasing EI NOx, consistent with earlier model simulations. The lowestHONO/NO,HONO/NOy and "was observed for the largest passenger aircraft A380.

In the present pilot study, an optimized LOPAP instrument for the detection of nitrous acid (HONO) in the atmosphere (DL 0.2 pptV) was tested at the high alpine research station "Jungfraujoch" at 3580 m altitude in the Swiss Alps under conditions comparable to polar regions. HONO concentrations in the range

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International audience; Results from an intercomparison of several currently used in-situ techniques for the measurement of atmospheric formaldehyde (CH2O) are presented. The measurements were carried out at Bresso, an urban site in the periphery of Milan (Italy) as part of the FORMAT-I field campaign. Eight instruments were employed by six independent research groups using four different techniques: Differential Optical Absorption Spectroscopy (DOAS), Fourier Transform Infra Red (FTIR) interferometry, the fluorimetric Hantzsch reaction technique (five instruments) and a chromatographic technique employing C18-DNPH-cartridges (2,4-dinitrophenylhydrazine). White type multi-reflection systems were employed for the optical techniques in order to avoid spatial CH2O gradients and ensure the sampling of nearly the same air mass by all instruments. Between 23 and 31 July 2002, up to 13 ppbv of CH2O were observed. The concentrations lay well above the detection limits of all instruments. The formaldehyde concentrations determined with DOAS, FTIR and the Hantzsch instruments were found to agree within ±11%, with the exception of one Hantzsch instrument, which gave systematically higher values. The two hour integrated samples by DNPH yielded up to 25% lower concentrations than the data of the continuously measuring instruments averaged over the same time period. The consistency between the DOAS and the Hantzsch method was better than during previous intercomparisons in ambient air with slopes of the regression line not significantly differing from one. The differences between the individual Hantzsch instruments could be attributed in part to the calibration standards used. Possible systematic errors of the methods are discussed.

In the present study, the heterogeneous conversion of nitrogen oxide (NO) and nitrogen dioxide (NO2) was studied at atmospheric humidity levels on flame soot surfaces, which were treated with gaseous nitric acid (HNO3). In addition, the heterogeneous reaction of HNO3 on soot was investigated at atmospheric humidity. For the treatment of soot by pure HNO3 only reversible uptake with a surface coverage of ~1?2×1014 HNO3 cm?2 was observed for HNO3 mixing ratios in the range 250?800 ppbv. Only for higher HNO3 mixing ratios of >800 ppbv the formation of NO and NO2 was observed. The results were not affected by the addition of NO. In none of the experiments with HNO3 the formation of nitrous acid (HONO) was observed. For HNO3 mixing ratios 2 and NO were found to be 2 with soot was not significantly affected when the soot surface was treated with gaseous HNO3 prior to the experiment. Only for high surface coverage of HNO3 the formation of HONO was suppressed in the initial phase of the reaction, probably caused by the blocking of active sites by adsorbed HNO3. Under the assumption that the experimental findings for the used model flame soot can be extrapolated to atmospheric soot particles, the results show that the reactions of HNO3 and HNO3+NO on soot surfaces are unimportant for a "renoxification" of the atmosphere and do not represent an atmospheric HONO source. In addition, the integrated HONO yield of ca. 1014 cm?2 in the reaction of NO2 with soot is not significantly influenced by simulated atmospheric processing of the soot surface by HNO3, and is still too small to explain HONO formation in the atmosphere.

The heterogeneous conversion of NO2 on different secondary organic aerosols (SOA) was investigated with the focus on a possible formation of nitrous acid (HONO). In one set of experiments different organic aerosols were produced in the reactions of O3 with alpha-pinene, limonene or catechol and OH radicals with toluene or limonene, respectively. The aerosols were sampled on filters and exposed to humidified NO2 mixtures under atmospheric conditions. The estimated upper limits for the uptake coefficients of NO2 and the reactive uptake coefficients NO2 -> HONO are in the range of 10-6 and 10-7, respectively. The integrated HONO formation for 1 h reaction time was 13 cm-2 geometrical surface and 17 g-1 particle mass. In a second set of experiments the conversion of NO2 into HONO in the presence of organic particles was carried out in an aerosol flow tube under atmospheric conditions. In this case the aerosols were produced in the reaction of O3 with beta-pinene, limonene or catechol, respectively. The upper limits for the reactive uptake coefficients NO2 -> HONO were in the range of 7 x 10-7 - 9 x 10-6. The results from the present study show that heterogeneous formation of nitrous acid on secondary organic aerosols (SOA) is unimportant for the atmosphere.