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

Development and characterization of a single particle laser ablation mass spectrometer (SPLAM) for organic aerosol studies

A single particle instrument was developed for real-time analysis of organic aerosol. This instrument, named Single Particle Laser Ablation Mass Spectrometry (SPLAM), samples particles using an aerodynamic lens system for which the theoretical performances were calculated. At the outlet of this system, particle detection and sizing are realized by using two continuous diode lasers operating at λ = 403 nm. Polystyrene Latex (PSL), sodium chloride (NaCl) and dioctylphtalate (DOP) particles were used to characterize and calibrate optical detection of SPLAM. The optical detection limit (DL) and detection efficiency (DE) were determined using size-selected DOP particles. The DE ranges from 0.1 to 90% for 100 and 350 nm DOP particles respectively and the SPLAM instrument is able to detect and size-resolve particles as small as 110–120 nm. During optical detection, particle scattered light from the two diode lasers, is detected by two photomultipliers and the detected signals are used to trigger UV excimer laser (λ = 248 nm) used for one-step laser desorption ionization (LDI) of individual aerosol particles. The formed ions are analyzed by a 1 m linear time-of-flight mass spectrometer in order to access to the chemical composition of individual particles. The TOF-MS detection limit for gaseous aromatic compounds was determined to be 0.85 × 10<sup>−15</sup> kg (∼4 × 10<sup>3</sup> molecules). DOP particles were also used to test the overall operation of the instrument. The analysis of a secondary organic aerosol, formed in a smog chamber by the ozonolysis of indene, is presented as a first application of the instrument. Single particle mass spectra were obtained with an effective hit rate of 8%. Some of these mass spectra were found to be very different from one particle to another possibly reflecting chemical differences within the investigated indene SOA particles. Our study shows that an exhaustive statistical analysis, over hundreds of particles, and adapted reference mass spectra are further needed to understand the chemical meaning of single particle mass spectra of chemically complex submicrometer-sized organic aerosols

Collision Dynamics and Solvation of Water Molecules in a Liquid Methanol Film

Environmental molecular beam experiments are used to examine water interactions with liquid methanol films at temperatures from 170 K to 190 K. We find that water molecules with 0.32 eV incident kinetic energy are efficiently trapped by the liquid methanol. The scattering process is characterized by an efficient loss of energy to surface modes with a minor component of the incident beam that is inelastically scattered. Thermal desorption of water molecules has a well characterized Arrhenius form with an activation energy of 0.47{\pm}0.11 eV and pre-exponential factor of 4.6 {\times} 10^(15{\pm}3) s^(-1). We also observe a temperature dependent incorporation of incident water into the methanol layer. The implication for fundamental studies and environmental applications is that even an alcohol as simple as methanol can exhibit complex and temperature dependent surfactant behavior.Comment: 8 pages, 5 figure

Frame Theory for Signal Processing in Psychoacoustics

This review chapter aims to strengthen the link between frame theory and signal processing tasks in psychoacoustics. On the one side, the basic concepts of frame theory are presented and some proofs are provided to explain those concepts in some detail. The goal is to reveal to hearing scientists how this mathematical theory could be relevant for their research. In particular, we focus on frame theory in a filter bank approach, which is probably the most relevant view-point for audio signal processing. On the other side, basic psychoacoustic concepts are presented to stimulate mathematicians to apply their knowledge in this field

Rethinking the law and politics of democratic police accountability

This paper evaluates the work and impact of a number of Police and Crime Commissioners (PCCs) in England and Wales and attempts to refocus public discourse and scrutiny on their Police and Crime Plans as a key prism through which their performance should be measured. Drawing upon the literature published by various PCCs, the Stevens Commission, the Home Affairs Committee and numerous academics, the paper will argue that a major reform of democratic police accountability in England and Wales is needed. Due to the often voluminous and piecemeal nature of the documents published on the PCCs’ websites, the textual analysis is limited to the Police and Crime Plans for Greater Manchester, the West Midlands and the London Metropolitan are

From silence to primary definer: The rise of the Intelligence lobby in the public sphere

Until the end of the Cold War the UK intelligence services were not officially acknowledged, and their personnel were banned from entering the public sphere. From 1989 the UK government began to put the intelligence services on a legal footing and to release the identity of the heads of the intelligence agencies. Since then, public engagement by the intelligence agencies has gathered pace. What this article hypothesises is that there is now, in the UK, an effective intelligence lobby of former insiders who engage in the public sphere – using on the record briefings – to counter criticism of the intelligence community and to promote a narrative and vision of what UK intelligence should do, how it is supported and how oversight is conducted. Content analysis and framing models of non-broadcast coverage of intelligence debates, focusing on the 36 months after the Snowden revelations, confirm an active and rolling lobby of current and former intelligence officials. The paper concludes that the extent of the lobby’s interventions in the public sphere is a matter for debate and possible concern