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 290–297 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 × 10<sup>−3</sup> s<sup>−1</sup>) for <i>J</i><sub>NO<sub>2</sub></sub> and (1.4 × 10<sup>−5</sup> s<sup>−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 α-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

Measurement of alkyl and multifunctional organic nitrates by proton-transfer-reaction mass spectrometry

A commercial PTR-TOF-MS has been optimized in order to allow the measurement of individual organic nitrates in the atmosphere. This has been accomplished by shifting the distribution between different ionizing analytes, H3O+∕ H3O+(H2O)n or NO+∕ NO2+. The proposed approach has been proven to be appropriate for the online detection of individual alkyl nitrates and functionalized nitrates. It has been shown that hydroxyl and ketonitrates have a high affinity towards NO+, leading to the formation of an adduct that allows the easy identification of the organic nitrate (R) from the R–NO+ ion signal. The recorded sensitivities for both ionization modes correspond to detection limits of tens of ppt min−1 in the case of hydroxy- and ketonitrates. Alkyl nitrates exhibit a moderate affinity towards NO+ ionization leading to detection units of few hundreds of ppt and the highest sensitivity in H3O+ mode was obtained for the water adducts signals. However, this method exhibits much lower capabilities for the detection of peroxyacetyl nitrates with detection limits in the ppb range

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 1.43–1.60 (±0.02) to 1.32–1.38 (±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 1.02–1.07 (±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

The Essential Role for Laboratory Studies in Atmospheric Chemistry

Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This article highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues. Laboratory studies provide rich opportunities to expand our understanding of the atmosphere via collaborative research with the modeling and field measurement communities, and with neighboring disciplines

The Essential Role for Laboratory Studies in Atmospheric Chemistry

Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This article highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues. Laboratory studies provide rich opportunities to expand our understanding of the atmosphere via collaborative research with the modeling and field measurement communities, and with neighboring disciplines

Nitrate radicals and biogenic volatile organic compounds: Oxidation, mechanisms, and organic aerosol

Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO3-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-The-Art chemical transport and chemistry-climate models. This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO3-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO3-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.The authors acknowledge support from the International Global Atmospheric Chemistry project (IGAC), the US National Science Foundation (NSF grants AGS-1541331 and AGS-1644979), and Georgia Tech College of Engineering and College of Sciences for support of the workshop on nitrate radicals and biogenic hydrocarbons that led to this review article. N. L. Ng acknowledges support from NSF CAREER AGS-1555034 and US Environmental Protection Agency STAR (Early Career) RD-83540301. S. S. Brown acknowledges support from the NOAA Atmospheric Chemistry, Carbon Cycle and Climate program. A. T. Archibald and B. Ouyang thank NERC for funding through NE/M00273X/1. E. Atlas acknowledges NSF grant AGS-0753200. R. C. Cohen acknowledges NSF grant AGS-1352972. J. N. Crowley acknowledges the Max Planck Society. J. L. Fry, D. A. Day, and J. L. Jimenez acknowledge support from the NOAA Climate Program Office’s AC4 program, award no. NA13OAR4310063 (Colorado)/NA13OAR4310070 (Reed). N. M. Donahue acknowledges NSF AGS-1447056. M. I. Guzman wishes to acknowledge support from NSF CAREER award (CHE-1255290). J. L. Jimenez and D. A. Day acknowledge support from NSF AGS-1360834 and EPA 83587701-0. R. McLaren acknowledges NSERC grant RGPIN/183982-2012. H. Herrmann, A. Tilgner, and A. Mutzel acknowledge the DARK KNIGHT project funded by DFG under HE 3086/25-1. B. Picquet-Varrault acknowledges support from the French National Agency for Research (project ONCEM-ANR-12-BS06-0017-01). R. H. Schwantes acknowledges NSF AGS-1240604. Y. Rudich and S. S. Brown acknowledge support from the USA-Israel Binational Science Foundation (BSF) grant no. 2012013. Y. Rudich acknowledges support from the Henri Gutwirth Foundation. J. Mao acknowledges support from the NOAA Climate Program Office grant no. NA13OAR4310071. J. A. Thornton acknowledges support from NSF AGS 1360745. B. H. Lee was supported by the NOAA Climate and Global Change Postdoctoral Fellowship. R. A. Zaveri acknowledges support from the US Department of Energy (DOE) Atmospheric System Research (ASR) program under contract DE-AC06-76RLO 1830 at Pacific Northwest National Laboratory

A new device for formaldehyde and total aldehydes real-time monitoring

AIR+MSA:CGOA new sensitive technique for the quantification of formaldehyde (HCHO) and total aldehydes has been developed in order to monitor these compounds, which are known to be involved in air quality issues and to have health impacts. Our approach is based on a colorimetric method where aldehydes are initially stripped from the air into a scrubbing solution by means of a turning coil sampler tube and then derivatised with 3-methylbenzothiazolinone-2-hydrazone in acid media (pH = -0.5). Hence, colourless aldehydes are transformed into blue dyes that are detected by UV-visible spectroscopy at 630 nm. Liquid core waveguide LCW TeflonA (R) AF-2400 tube was used as innovative optical cells providing a HCHO detection limit of 4 pptv for 100 cm optical path with a time resolution of 15 min. This instrument showed good correlation with commonly used techniques for aldehydes analysis such as DNPH derivatisation chromatographic techniques with off-line and on-line samplers, and DOAS techniques (with deviation below 6 %) for both indoor and outdoor conditions. This instrument is associated with simplicity and low cost, which is a prerequisite for indoor monitoring

Non-Voigt line-shape effects on retrievals of atmospheric ozone: Line-mixing effects

International audienceA theoretical approach is proposed to model line-mixing (LM) effects on absorption coefficients of O3 perturbed by N2 and air. It uses state-to-state rotational cross-sections calculated with a semi-classical approach and two empirical parameters, which enable switching from the state space to the line space. The first, associated with couplings within Q branches is deduced from a room temperature far-infrared spectrum. The second, governing line-couplings between R (or P) lines, is determined from a spectrum measured in the ν1+ν2+ν3 band. The model developed is then successfully compared with measurements performed at room temperature for a relatively large range of pressure (0.7–8 atm) and in four different bands (from 3 to 300 μm). Accurate predictions are, in particular, obtained in the 10 μm (ν1, ν3) region, which is widely used for remote sensing purposes. Consequences of LM effects on retrievals of ozone atmospheric volume mixing ratios are then studied using simulated atmospheric spectra. The results show that LM leads to systematic spectra fit residuals and errors on the retrieved ozone amounts, which are small but might be detectable in measured atmospheric spectra