Determination of Equilibrium Constants for the Reaction between Acetone and HO_2 Using Infrared Kinetic Spectroscopy

The reaction between the hydroperoxy radical, HO_2, and acetone may play an important role in acetone removal and the budget of HO_x radicals in the upper troposphere. We measured the equilibrium constants of this reaction over the temperature range of 215–272 K at an overall pressure of 100 Torr using a flow tube apparatus and laser flash photolysis to produce HO_2. The HO_2 concentration was monitored as a function of time by near-IR diode laser wavelength modulation spectroscopy. The resulting [HO_2] decay curves in the presence of acetone are characterized by an immediate decrease in initial [HO_2] followed by subsequent decay. These curves are interpreted as a rapid (<100 μs) equilibrium reaction between acetone and the HO_2 radical that occurs on time scales faster than the time resolution of the apparatus, followed by subsequent reactions. This separation of time scales between the initial equilibrium and ensuing reactions enabled the determination of the equilibrium constant with values ranging from 4.0 × 10^(–16) to 7.7 × 10^(–1)8 cm^3 molecule^(–1) for T = 215–272 K. Thermodynamic parameters for the reaction determined from a second-law fit of our van’t Hoff plot were Δ_(r)H°_(245) = −35.4 ± 2.0 kJ mol^(–1) and Δ_(r)S°_(245) = −88.2 ± 8.5 J mol^(–1) K^(–1). Recent ab initio calculations predict that the reaction proceeds through a prereactive hydrogen-bonded molecular complex (HO_2–acetone) with subsequent isomerization to a hydroxy–peroxy radical, 2-hydroxyisopropylperoxy (2-HIPP). The calculations differ greatly in the energetics of the complex and the peroxy radical, as well as the transition state for isomerization, leading to significant differences in their predictions of the extent of this reaction at tropospheric temperatures. The current results are consistent with equilibrium formation of the hydrogen-bonded molecular complex on a short time scale (100 μs). Formation of the hydrogen-bonded complex will have a negligible impact on the atmosphere. However, the complex could subsequently isomerize to form the 2-HIPP radical on longer time scales. Further experimental studies are needed to assess the ultimate impact of the reaction of HO_2 and acetone on the atmosphere

Aromatic acids in a Eurasian Arctic ice core: a 2,600-year proxy record of biomass burning

Wildfires and their emissions have significant impacts on ecosystems, climate, atmospheric chemistry, and carbon cycling. Well-dated proxy records are needed to study the long-term climatic controls on biomass burning and the associated climate feedbacks. There is a particular lack of information about long-term biomass burning variations in Siberia, the largest forested area in the Northern Hemisphere. In this study we report analyses of aromatic acids (vanillic and para-hydroxybenzoic acids) over the past 2600 years in the Eurasian Arctic Akademii Nauk ice core. These compounds are aerosol-borne, semi-volatile organic compounds derived from lignin combustion. The analyses were made using ion chromatography with electrospray mass spectrometric detection. The levels of these aromatic acids ranged from below the detection limit (0.01 to 0.05 ppb; 1 ppb  =  1000 ng L−1) to about 1 ppb, with roughly 30 % of the samples above the detection limit. In the preindustrial late Holocene, highly elevated aromatic acid levels are observed during three distinct periods (650–300 BCE, 340–660 CE, and 1460–1660 CE). The timing of the two most recent periods coincides with the episodic pulsing of ice-rafted debris in the North Atlantic known as Bond events and a weakened Asian monsoon, suggesting a link between fires and large-scale climate variability on millennial timescales. Aromatic acid levels also are elevated during the onset of the industrial period from 1780 to 1860 CE, but with a different ratio of vanillic and para-hydroxybenzoic acid than is observed during the preindustrial period. This study provides the first millennial-scale record of aromatic acids. This study clearly demonstrates that coherent aromatic acid signals are recorded in polar ice cores that can be used as proxies for past trends in biomass burning

Hard Drive Crash: An Examination of Liability for Self-Driving Vehicles

This analysis considers the potential impacts of completely self-driving vehicles on vehicular liability. This begins with examining how such vehicles might be treated under an evolution of the current liability system, and the potential results of attributing liability to an operator, the vehicle itself, different manufacturers, and a government entity. Discussion then turns to how liability might be altered prospectively in order to incentivize outcomes beneficial to both consumers and creators from a public policy perspective. This includes a proposal of how such a proposal might be structured. Focal points include public policy, social acceptance, and potential incidental problems raised

A Recipe for Literacy: Making Meaning Through Cake

Within this article, we explore cake artistry as a means of demonstrating a process of meaning-making (Starratt, 1996). We contend that the cakes themselves are tactile examples of literacy events (Heath, 1982) due to the embodiment and relationality present within their design process (Johnson et al., 2020). This article discusses two unique cakes that explore elements of literacy related to storytelling, personal reflection, and emotional expression. We, the authors, strive to position literacy, as explored through cakes, within a post-humanist perspective and provide an opportunity for authentic engagement and humanized/ing actions with meaning-making (Beucher et al., 2019; Garrett et al., 2019; Perry &amp; Medina, 2015). We hope that this article will encourage our readers to think about literacy differently as well as what it means to be “literate” within different professions.  

A Risk-based Approach to AI Regulation: System Categorisation and Explainable AI Practices

The regulation of artificial intelligence (AI) presents a challenging new legal frontier that is only just beginning to be addressed around the world. This article provides an examination of why regulation of AI is difficult, with a particular focus on understanding the reasoning behind automated decisions. We go on to propose a flexible, risk-based categorisation for AIbased on system inputs and outputs, and incorporate explainable AI (XAI) into our novel categorisation to provide the beginnings of a functional and scalable AI regulatory framework

Sea ice and pollution-modulated changes in Greenland ice core methanesulfonate and bromine

Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its future evolution. Methanesulfonate (MSA) and bromine concentrations preserved in ice cores have both been proposed as indicators of past sea ice conditions. In this study, two ice cores from central and north-eastern Greenland were analysed at sub-annual resolution for MSA (CH3SO3H) and bromine, covering the time period 1750–2010. We examine correlations between ice core MSA and the HadISST1 ICE sea ice dataset and consult back trajectories to infer the likely source regions. A strong correlation between the low-frequency MSA and bromine records during pre-industrial times indicates that both chemical species are likely linked to processes occurring on or near sea ice in the same source regions. The positive correlation between ice core MSA and bromine persists until the mid-20th century, when the acidity of Greenland ice begins to increase markedly due to increased fossil fuel emissions. After that time, MSA levels decrease as a result of declining sea ice extent but bromine levels increase. We consider several possible explanations and ultimately suggest that increased acidity, specifically nitric acid, of snow on sea ice stimulates the release of reactive Br from sea ice, resulting in increased transport and deposition on the Greenland ice sheet

Mapping for Social Justice

Mapping Hate Crime in the United StatesHate crime is a national human rights problem. Incidents are rising, but statistics are unreliable. The need for a publicly available resource documenting hate crimes is great, yet accurate data are not available. The Hate Crime Map addresses this need by providing a crowd-sourced platform where victims can report incidents. The map offers data and sophisticated visualizations by state &amp; county of the types &amp; cause (race, gender, religion) of the attacks. This panel will introduce the map.Metamap: Building a More Accessible Campus MapMetamap is a student-initiated collaborative project to improve the UCLA campus map for people with disabilities. We aim to log accessible assets, routes, and maintenance issues that pose a threat to accessibility. Our project is an example of the synergies between various different campus entities, including student government, to use GIS for the benefit of the entire campus community