Aircraft assessment of trace compound fluxes in the atmosphere with relaxed eddy Accumulation: Sensitivity to the conditions of selection

International audienceThe Relaxed Eddy Accumulation (REA) technique, implemented aboard aircraft, may be used to measure a wide variety of trace gas fluxes at a regional scale. Its principle is rather simple: air is sampled at a constant rate and the flux is calculated by multiplying a constant [• (0.58 in field experiment and 0.62 in simulations) by the standard deviation of the vertical velocity and by the difference between the average concentrations of the scalar (trace gas) for updrafts and downdrafts. The storage of the chemical compound in reservoirs allows for trace gas analysis in laboratory, when in situ measurement with fast response and high sensitivity sensors are not available. The REA method was implemented on the Avion de Recherche Atmosphdrique et de Tdldddtection aircraft during the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO) campaign. The main requirement for accurate flux determination is the measurement of the vertical component of wind velocity in real time. A simulation technique was developed to evaluate the performance of an aircraft REA. The influence of the time lag between the vertical velocity (W) measurement and REA control was tested, as well as the offset of W, the threshold, and the filtering imposed on W. Correction factors, used in a deployment of aircraft REA, were deduced from this study. An additional simulation was performed to evaluate the influence of spatial or temporal drifts on the scalar. The simulation showed that the REA Inethod is not more disturbed than the Eddy Correlation method by low frequencies of physical origin, such as topography. The REA method was used during EXPRESSO for the measurement of isoprene fluxes over the wet savanna and the evergreen rain forest

Irradiation up-regulates CD80 expression through two different mechanisms in spleen B cells, B lymphoma cells, and dendritic cells

We have previously demonstrated irradiation-induced up-regulation of CD80 expression in A20-HL B lymphoma cells by inducing expression of tumour necrosis factor-α (TNF-α) and CD154. In the present study, we investigated whether irradiation also up-regulates CD80 expression in mouse spleen B cells. Because freshly prepared spleen B cells are highly sensitive to irradiation, we employed spleen B cells stimulated with lipopolysaccharide (LPS-B cells). X-irradiation (8 Gy) followed by incubation (9–12 hr) highly and selectively up-regulated CD80 expression in LPS-B cells, whereas the same treatment slightly increased expression of CD54 and did not affect expression of CD86, major histocompatibility complex class II, CD11a or surface immunoglobulin M. The irradiation-induced up-regulation of CD80 expression resulted in enhanced APC function of LPS-B cells. Up-regulation of CD80 expression on LPS-B cells was accompanied by an increase in CD80 mRNA accumulation and nuclear factor (NF)-κB activation. Activation of NF-κB was shown to be critical for up-regulation of CD80 expression as pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB, severely decreased the observed up-regulation. X-irradiation of LPS-B cells induced expression of TNF-α but not CD154. However, anti-TNF-α monoclonal antibody (mAb) with anti-CD154 mAb did not inhibit X-irradiation-induced up-regulation of CD80 expression in LPS-B cells, whereas these mAbs almost completely inhibited this up-regulation in A20-HL cells and bone marrow-derived dendritic cells (DCs). In contrast, a thiol antioxidant, N-acetyl-l-cysteine, completely blocked X-irradiation-induced up-regulation of CD80 expression in LPS-B cells, but not in A20-HL cells or in DCs. Based on these findings, we concluded that X-irradiation up-regulates CD80 expression not only in A20-HL cells and DCs but also in LPS-B cells, and that this up-regulation in LPS-B cells via NF-κB activation is dependent on the generation of reactive oxygen species, while that in A20-HL cells and DCs is not