73 research outputs found
Design of a new multi-phase experimental simulation chamber for atmospheric photosmog, aerosol and cloud chemistry research
A new simulation chamber has been built at the Interuniversitary Laboratory of Atmospheric Systems (LISA). The CESAM chamber (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber) is designed to allow research in multiphase atmospheric (photo-) chemistry which involves both gas phase and condensed phase processes including aerosol and cloud chemistry. CESAM has the potential to carry out variable temperature and pressure experiments under a very realistic artificial solar irradiation. It consists of a 4.2 m<sup>3</sup> stainless steel vessel equipped with three high pressure xenon arc lamps which provides a controlled and steady environment. Initial characterization results, all carried out at 290â297 K under dry conditions, concerning lighting homogeneity, mixing efficiency, ozone lifetime, radical sources, NO<sub>y</sub> wall reactivity, particle loss rates, background PM, aerosol formation and cloud generation are given. Photolysis frequencies of NO<sub>2</sub> and O<sub>3</sub> related to chamber radiation system were found equal to (4.2 Ă 10<sup>&minus;3</sup> s<sup>&minus;1</sup>) for <i>J</i><sub>NO<sub>2</sub></sub> and (1.4 Ă 10<sup>&minus;5</sup> s<sup>&minus;1</sup>) for <i>J</i><sub>O<sup>1</sup>D</sub> which is comparable to the solar radiation in the boundary layer. An auxiliary mechanism describing NO<sub>y</sub> wall reactions has been developed. Its inclusion in the Master Chemical Mechanism allowed us to adequately model the results of experiments on the photo-oxidation of propene-NO<sub>x</sub>-Air mixtures. Aerosol yields for the &alpha;-pinene + O<sub>3</sub> system chosen as a reference were determined and found in good agreement with previous studies. Particle lifetime in the chamber ranges from 10 h to 4 days depending on particle size distribution which indicates that the chamber can provide high quality data on aerosol aging processes and their effects. Being evacuable, it is possible to generate in this new chamber clouds by fast expansion or saturation with or without the presence of pre-existing particles, which will provide a multiphase environment for aerosol-droplet interaction
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Relating hygroscopicity and optical properties to chemical composition and structure of secondary organic aerosol particles generated from the ozonolysis of α-pinene
Secondary organic aerosol (SOA) were generated from the ozonolysis of α-pinene in the CESAM (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber) simulation chamber. The SOA formation and aging were studied by following their optical, hygroscopic and chemical properties. The optical properties were investigated by determining the particle complex refractive index (CRI). The hygroscopicity was quantified by measuring the effect of relative humidity (RH) on the particle size (size growth factor, GF) and on the scattering coefficient (scattering growth factor, f(RH)). The oxygen to carbon atomic ratios (O : C) of the particle surface and bulk were used as a sensitive parameter to correlate the changes in hygroscopic and optical properties of the SOA composition during their formation and aging in CESAM.
The real CRI at 525 nm wavelength decreased from 1.43â1.60 (±0.02) to 1.32â1.38 (±0.02) during the SOA formation. The decrease in the real CRI correlated to the O : C decrease from 0.68 (±0.20) to 0.55 (±0.16). In contrast, the GF remained roughly constant over the reaction time, with values of 1.02â1.07 (±0.02) at 90% (±4.2%) RH. Simultaneous measurements of O : C of the particle surface revealed that the SOA was not composed of a homogeneous mixture, but contained less oxidised species at the surface which may limit water absorption. In addition, an apparent change in both mobility diameter and scattering coefficient with increasing RH from 0 to 30% was observed for SOA after 14 h of reaction. We postulate that this change could be due to a change in the viscosity of the SOA from a predominantly glassy state to a predominantly liquid state
Secondary organic aerosol formation from isoprene photooxidation during cloud condensation-evaporation cycles
Abstract. The impact of cloud events on isoprene secondary organic aerosol (SOA) formation has been studied from an isopreneâŻââŻNOxâŻââŻlight system in an atmospheric simulation chamber. It was shown that the presence of a liquid water cloud leads to a faster and higher SOA formation than under dry conditions. When a cloud is generated early in the photooxidation reaction, before any SOA formation has occurred, a fast SOA formation is observed with mass yields ranging from 0.002 to 0.004. These yields are 2 and 4 times higher than those observed under dry conditions. When the cloud is generated at a later photooxidation stage, after isoprene SOA is stabilized at its maximum mass concentration, a rapid increase (by a factor of 2 or higher) of the SOA mass concentration is observed. The SOA chemical composition is influenced by cloud generation: the additional SOA formed during cloud events is composed of both organics and nitrate containing species. This SOA formation can be linked to the dissolution of water soluble volatile organic compounds (VOCs) in the aqueous phase and to further aqueous phase reactions. Cloud-induced SOA formation is experimentally demonstrated in this study, thus highlighting the importance of aqueous multiphase systems in atmospheric SOA formation estimations.
The authors thank Arnaud Allanic, Sylvain Ravier, Pascal Renard and Pascal Zapf for their contributions in the experiments. The authors also acknowledge the institutions that have provided financial support: the French National Institute for Geophysical Research (CNRS-INSU) within the LEFE-CHAT program through the project âImpact de la chimie des nuages sur la formation dâaĂ©rosols organiques secondaires dans lâatmosphĂšreâ and the French National Agency for Research (ANR) project CUMULUS ANR-2010-BLAN-617-01. This work was also supported by the EC within the I3 project âIntegrating of European Simulation Chambers for Investigating Atmospheric Processesâ (EUROCHAMP-2, contract no. 228335). The authors thank the MASSALYA instrumental platform (Aix Marseille UniversitĂ©, lce.univ-amu.fr) for the analysis and measurements used in this paper.This is the final version of the article. It first appeared from Copernicus Publications via http://dx.doi.org/10.5194/acp-16-1747-201
Spectral- and size-resolved mass absorption efficiency of mineral dust aerosols in the shortwave spectrum: a simulation chamber study
This paper presents new laboratory measurements
of the mass absorption efficiency (MAE) between 375 and
850 nm for 12 individual samples of mineral dust from different
source areas worldwide and in two size classes: PM10:6
(mass fraction of particles of aerodynamic diameter lower
than 10.6 \u3bcm) and PM2:5 (mass fraction of particles of aerodynamic
diameter lower than 2.5 \u3bcm). The experiments were
performed in the CESAM simulation chamber using mineral
dust generated from natural parent soils and included optical
and gravimetric analyses.
The results show that the MAE values are lower for
the PM10:6 mass fraction (range 37\u2013135x10-3 m2 g-1 at
375 nm) than for the PM2:5 (range 95\u2013711x10-3 m2 g-1 at
375 nm) and decrease with increasing wavelength as lambda-AAE,
where the \uc5ngstr\uf6m absorption exponent (AAE) averages
between 3.3 and 3.5, regardless of size. The size independence
of AAE suggests that, for a given size distribution, the oxide fraction, which could ease the application and the validation
of climate models that now start to include the representation
of the dust composition, as well as for remote
sensing of dust absorption in the UV\u2013vis spectral region
Complex refractive index and single scattering albedo of Icelandic dust in the shortwave part of the spectrum
Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by
changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the
spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering
albedo (SSA) and the complex refractive index (m=n-ik) of Icelandic dust from five major emission hotspots were retrieved between
370â950ânm using online measurements of size distribution and spectral absorption (ÎČabs) and scattering (ÎČsca)
coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured
ÎČabs and ÎČsca increased from 0.90â0.94 at 370ânm to 0.94â0.96 at 950ânm in Icelandic dust from the
different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was
retrieved by minimizing the differences between the measured ÎČabs and ÎČsca and those computed using the Mie theory for
spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive
index (n(λ)) was found to be 1.60â1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was
almost constant with wavelength and was found to be around 0.004 at 370ânm and 0.002â0.003 at 950ânm. The estimated complex
refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed
in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust
are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing
towards the near-infrared. In Icelandic dust, k(λ) between 660â950ânm was 2â8 times higher than most of the dust samples sourced
in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has
not been accounted for in climate predictions.</p
Reflection spectroscopy study of the <SUP>16</SUP>O<SUP>12</SUP>C<SUP>16</SUP>O Μ<SUB>3</SUB>-band lines
International audienceReflection spectra of pure CO2 gas have been recorded in the 4.3 Ό m region by using a high resolution Fourier transform spectrometer, providing measured values of the refractive index. Comparisons with the results of calculations using available spectroscopic data, and free of any adjusted line parameter, show a very good agreement. This confirms that this experimental technique provides an alternative approach for the test or determination of spectroscopic parameters. Its advantages for studies of extremely strongly absorbing species and investigations of spatially (tightly) confined molecular gases are discussed
The benefits of the PCR-its/filter paper in the diagnosis of parasites and chemoresistant trypanosomes
The most reliable diagnosis method of animal trypanosomoses often used is the microscopic examination for motile trypanosomes. However, the sensitivity of this method remains relatively lower than the classic PCR (Polymerase Chain Reaction). This latter, besides of its high cost, requires some conditions which sometimes are difficult to apply on the field (conservation of samples at +4°C or -20°C). In this study, buffy coat (BCT) specimens were dotted on the filter paper and conserved during 12 months(September 2004 - October 2005) at ambient temperature until their treatment with ChelexÂź 5%. Samples were tested using unique âpantrypanosomiqueâ PCR with ITS (Internal Transcribed Spacer) primers. This PCR using polyspecific primers indicated parasitological prevalences of 1.2 to 6.2 times higher than those recorded by the microscopic analysis of the buffy coat on the same samples. Beside the mixed infectionswhich could be detected by one PCR reaction, this method could also distinguish Trypanosoma congolense savanna type from Trypanosoma congolense forest type. The gain of sensitivity and the easy conservationof samples in this method could be used for the detection of the chemoresistance in low parasitological prevalence areas
Intercomparison of IBBCEAS, NitroMAC and FTIR analyses for HONO, NO2and CH2O measurements during the reaction of NO2 with H2O vapour in the simulation chamber CESAM
International audienceAbstract. We report on applications of the ultraviolet-light-emitting-diode-based incoherent broadband cavity-enhanced absorption spectroscopy (UV-LED-IBBCEAS) technique for optical monitoring of HONO, NO2 and CH2O in a simulation chamber. Performance intercomparison of UV-LED-IBBCEAS with a wet chemistry-based NitroMAC sensor and a Fourier transform infrared (FTIR) spectrometer has been carried out on real-time simultaneous measurement of HONO, NO2 and CH2O concentrations during the reaction of NO2 with H2O vapour in CESAM (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber). The 1Ï (signal-to-noise ratio (SNR)â=â1) detection limits of 112âpptv for NO2, 56âpptv for HONO and 41âppbv for CH2O over 120âs were found for the UV-LED-IBBCEAS measurement. On the contrary to many set-ups where cavities are installed outside the simulation chamber, we describe here an original in situ permanent installation. The intercomparison results demonstrate that IBBCEAS is a very well suitable technique for in situ simultaneous measurements of multiple chemically reactive species with high sensitivity and high precision even if the absorption bands of these species are overlapped. It offers excellent capacity for non-invasive optical monitoring of chemical reactions without any perturbation. For the application to simulation chambers, it has the advantage to provide a spatially integrated measurement across the reactor and hence to avoid point-sampling-related artefacts
Activation of kerosene soot to cloud condensation nuclei when exposed to OH, O3 and SO2
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Impact of the exposure of kerosene soot to O3 and SO2 on its hygroscopic properties
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