Halogenated organic species over the tropical rainforest

International audienceAirborne measurements of the halogenated trace gases methyl chloride, methyl bromide and chloroform were conducted over the Atlantic Ocean and 1000 km of pristine tropical rainforest in Suriname and French Guyana (3–6° N, 51–59° W) in October 2005. In the boundary layer (0–1.4 km), maritime air masses initially low in forest hydrocarbons, advected over the forest by southeasterly trade winds, were measured at various distances from the coast. Since the organohalogens presented here have relatively long atmospheric lifetimes (0.4–1.0 years) in comparison to the transport times (1–2 days), emissions will accumulate in air traversing the rainforest. The distributions of methyl chloride, methyl bromide and chloroform were analyzed as a function of forest contact time and the respective relationship used to determine fluxes from the rainforest during the long dry season. Emission fluxes have been calculated for methyl chloride and chloroform as 9.4 (±4.0 2s) and 0.34 (0.14± 2s) µg m-2 h-1, respectively. No significant flux from the rainforest was observed for methyl bromide within the limits of these measurements. The flux of methyl chloride was in general agreement with the flux measured over the same region in March 1998 during the LBA Claire project using a different analytical system. This confirms that the rainforest is a strong source for methyl chloride and suggests that this emission is relatively uniform throughout the year. In contrast the chloroform flux derived here is a factor of three less than previous measurements made in March 1998 suggesting a pronounced ecosystem variation. The differences in chloroform fluxes could not be attributed to either temperature or rainfall changes. The global extrapolation of the derived fluxes led to 1.5 (±0.6 2s) Tg yr-1 for methyl chloride, which is in the range of the missing source postulated by previous model studies and 55 (±22 2s) Gg yr-1 for chloroform

Physical and optical properties of 2010 Eyjafjallajökull volcanic eruption aerosol: ground-based, Lidar and airborne measurements in France

International audienceDuring the Eyjafjallajökull eruption (14 April to 24 May 2010), the volcanic aerosol cloud was observed across Europe by several airborne in situ and ground-based remote-sensing instruments. On 18 and 19 May, layers of depolarizing particles (i.e. non-spherical particles) were detected in the free troposphere above the Puy de Dôme station, (PdD, France) with a Rayleigh-Mie LIDAR emitting at a wavelength of 355 nm, with parallel and crossed polarization channels. These layers in the free troposphere (FT) were also well captured by simulations with the Lagrangian particle dispersion model FLEXPART, which furthermore showed that the ash was eventually entrained into the planetary boundary layer (PBL). Indeed, the ash cloud was then detected and characterized with a comprehensive set of in situ instruments at the Puy de Dôme station (PdD). In agreement with the FLEXPART simulation, up to 65 μg m−3 of particle mass and 2.2 ppb of SO2 were measured at PdD, corresponding to concentrations higher than the 95 percentile of 2 yr of measurements at PdD. Moreover, the number concentration of particles increased to 24 000 cm−3, mainly in the submicronic mode, but a supermicronic mode was also detected with a modal diameter of 2 μm. The resulting optical properties of the ash aerosol were characterized by a low scattering Ångström exponent (0.98), showing the presence of supermicronic particles. For the first time to our knowledge, the combination of in situ optical and physical characterization of the volcanic ash allowed the calculation of the mass-to-extinction ratio (η) with no assumptions on the aerosol density. The mass-to-extinction ratio was found to be significantly different from the background boundary layer aerosol (max: 1.57 g m−2 as opposed to 0.33 ± 0.03 g m−2). Using this ratio, ash mass concentration in the volcanic plume derived from LIDAR measurements was found to be 655 ± 23 μg m−3 when the plume was located in the FT (3000 m above the sea level - a.s.l.). This ratio could also be used to retrieve an aerosol mass concentration of 579 ± 60 μg m−3 on 19 April, when LIDAR observations detected the ash cloud at 3000 m a.s.l. in correspondence with model simulations (FLEXPART). On 22 April, another ash plume entered the BL, and although it was more diluted than during the May episode, the French research aircraft ATR42 that passed over Clermont-Ferrand in the PBL confirmed the presence of particles with a supermicronic mode, again with a modal diameter at 2 μm. This data set combining airborne, ground-based and remote sensing observations with dispersion model simulations shows an overall very good coherence during the volcanic eruption period, which allows a good confidence in the characteristics of the ash particles that can be derived from this unique data set

Study of the unknown HONO daytime source at a European suburban site during the MEGAPOLI summer and winter field campaigns

International audienceNitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NOx , O3 , photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity , wind speed and wind direction), black carbon concentration , total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell-shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h−1 and 0.25 ppb h−1 , during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J (NO2) and the product between J (NO2) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring at ground surface and involving water content available on the ground. Published by Copernicus Publications on behalf of the European Geosciences Union. 2806 V. Michoud et al.: Study of the unknown HONO daytime sourc

Autoantibodies against type I IFNs in patients with critical influenza pneumonia

In an international cohort of 279 patients with hypoxemic influenza pneumonia, we identified 13 patients (4.6%) with autoantibodies neutralizing IFN-alpha and/or -omega, which were previously reported to underlie 15% cases of life-threatening COVID-19 pneumonia and one third of severe adverse reactions to live-attenuated yellow fever vaccine. Autoantibodies neutralizing type I interferons (IFNs) can underlie critical COVID-19 pneumonia and yellow fever vaccine disease. We report here on 13 patients harboring autoantibodies neutralizing IFN-alpha 2 alone (five patients) or with IFN-omega (eight patients) from a cohort of 279 patients (4.7%) aged 6-73 yr with critical influenza pneumonia. Nine and four patients had antibodies neutralizing high and low concentrations, respectively, of IFN-alpha 2, and six and two patients had antibodies neutralizing high and low concentrations, respectively, of IFN-omega. The patients' autoantibodies increased influenza A virus replication in both A549 cells and reconstituted human airway epithelia. The prevalence of these antibodies was significantly higher than that in the general population for patients 70 yr of age (3.1 vs. 4.4%, P = 0.68). The risk of critical influenza was highest in patients with antibodies neutralizing high concentrations of both IFN-alpha 2 and IFN-omega (OR = 11.7, P = 1.3 x 10(-5)), especially those <70 yr old (OR = 139.9, P = 3.1 x 10(-10)). We also identified 10 patients in additional influenza patient cohorts. Autoantibodies neutralizing type I IFNs account for similar to 5% of cases of life-threatening influenza pneumonia in patients <70 yr old

Les composés organiques volatils dans les vallées alpines (sources, évolutions et transformations)

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Evidence of the impact of deep convection on reactive Volatile Organic Compounds in the upper tropical troposphere during the AMMA experiment in West Africa

International audienceA large dataset of reactive trace gases was collected for the first time over West Africa during the African Monsoon Multidisciplinary Analysis (AMMA) field experiment in August 2006. Volatile Organic Compounds (VOC from C5-C9) were measured onboard the two French aircrafts the ATR-42 and the Falcon-20 by a new instrument AMOVOC (Airborne Measurement Of Volatile Organic Compounds). The goal of this study is (i) to characterize VOC distribution in the tropical region of West Africa (ii) to determine the impact of deep convection on VOC distribution and chemistry in the tropical upper troposphere (UT) and (iii) to characterize its spatial and temporal extensions. Experimental strategy consisted in sampling at altitudes between 0 and 12 km downwind of Mesoscale Convective Systems (MCS) and at cloud base. Biogenic and anthropogenic VOC distribution in West Africa is clearly affected by North to South emission gradient. Isoprene, the most abundant VOC, is at maximum level over the forest (1.26 ppb) while benzene reaches its maximum over the urban areas (0.11 ppb). First, a multiple physical and chemical tracers approach using CO, O3 and relative humidity was implemented to distinguish between convective and non-convective air masses. Then, additional tools based on VOC observations (tracer ratios, proxy of emissions and photochemical clocks) were adapted to characterize deep convection on a chemical, spatial and temporal basis. VOC vertical profiles show a "C-shaped" trend indicating that VOC-rich air masses are transported from the surface to the UT by deep convective systems. VOC mixing ratios in convective outflow are up to two times higher than background levels even for reactive and short-lived VOC (e.g. isoprene up to 0.19 ppb at 12 km-altitude) and are dependent on surface emission type. As a consequence, UT air mass reactivity increases from 0.52 s−1 in non-convective conditions to 0.95 s−1 in convective conditions. Fractions of boundary layer air contained in convective outflow are estimated to be 40 ± 15%. Vertical transport timescale is calculated to be 25 ± 10 min between 0 to 12 km altitude. These results characterize deep convection occurring over West Africa and provide relevant information for tropical convection parameterization in regional/global models