The influence of physical state on shikimic acid ozonolysis: a case for in situ microspectroscopy

Atmospheric soluble organic aerosol material can become solid or semi-solid. Due to increasing viscosity and decreasing diffusivity, this can impact important processes such as gas uptake and reactivity within aerosols containing such substances. This work explores the dependence of shikimic acid ozonolysis on humidity and thereby viscosity. Shikimic acid, a proxy for oxygenated reactive organic material, reacts with O3 in a Criegee-type reaction. We used an environmental microreactor embedded in a scanning transmission X-ray microscope (STXM) to probe this oxidation process. This technique facilitates in situ measurements with single micron-sized particles and allows to obtain near-edge X-ray absorption fine structure (NEXAFS) spectra with high spatial resolution. Thus, the chemical evolution of the interior of the particles can be followed under reaction conditions. The experiments show that the overall degradation rate of shikimic acid is depending on the relative humidity in a way that is controlled by the decreasing diffusivity of ozone with decreasing humidity. This decreasing diffusivity is most likely linked to the increasing viscosity of the shikimic acid–water mixture. The degradation rate was also depending on particle size, most congruent with a reacto-diffusion limited kinetic case where the reaction progresses only in a shallow layer within the bulk. No gradient in the shikimic acid concentration was observed within the bulk material at any humidity indicating that the diffusivity of shikimic acid is still high enough to allow its equilibration throughout the particles on the timescale of hours at higher humidity and that the thickness of the oxidized layer under dry conditions, where the particles are solid, is beyond the resolution of STXM

Viscosity controls humidity dependence of N2O5 uptake to citric acid aerosol

The heterogeneous loss of dinitrogen pentoxide (N2O5) to aerosol particles has a significant impact on the night-time nitrogen oxide cycle and therefore the oxidative capacity in the troposphere. Using a N-13 short-lived radioactive tracer method, we studied the uptake kinetics of N2O5 on citric acid aerosol particles as a function of relative humidity (RH). The results show that citric acid exhibits lower reactivity than similar dicarboxylic and polycarboxylic acids, with uptake coefficients between similar to 3 x 10(-4)-similar to 3 x 10(-3) depending on humidity (17-70% RH). At RH above 50 %, the magnitude and the humidity dependence can be best explained by the viscosity of citric acid as compared to aqueous solutions of simpler organic and inorganic solutes and the variation of viscosity with RH and, hence, diffusivity in the organic matrix. Since the diffusion rates of N2O5 in highly concentrated citric acid solutions are not well established, we present four different parameterizations of N2O5 diffusivity based on the available literature data or estimates for viscosity and diffusivity of H2O. Above 50% RH, uptake is consistent with the reacto-diffusive kinetic regime whereas below 50% RH, the uptake coefficient is higher than expected from hydrolysis of N2O5 within the bulk of the particles, and the uptake kinetics is most likely limited by loss on the surface only. This study demonstrates the impact of viscosity in highly oxidized and highly functionalized secondary organic aerosol material on the heterogeneous chemistry of N2O5 and may explain some of the unexpectedly low loss rates to aerosol derived from field studies

Cyborg Tales: The Reinvention of the Human in the Information Age

The emerging technological developments across various scientific fields have brought about radical changes in the ways we perceive and define what it means to be human in today’s highly technologically oriented society. Advancements in robotics, AI research, molecular biology, genetic engineering, nanotechnology, medicine, etc., are mostly still in an experimental phase but it is likely that they will become a part of our daily experience. However, human enhancement and emergence of autonomous artificial beings have long been a part of futures imagined in SF and cyberpunk. While focusing on the phenomenon of cyborg as a product of both social reality and fiction, this chapter will attempt to offer a new perspective on selected SF and cyberpunk narratives by treating them not only as fictions but as theories of the future as well. Furthermore, selected examples of the existing real-life cyborgs will show that SF narratives are not merely limited to the scope of imagination but are a constituent part of lived experience, thus blurring the boundaries between reality and fiction