Asymptomatic carotid stenosis is associated with circadian and other variability in embolus detection

Background and Purpose: Variability in transcranial Doppler (TCD) detection of embolic signals (ES) is important for risk stratification. We tested the effect of time of day on ES associated with 60–99% asymptomatic carotid stenosis. Materials and Methods: Subjects were from the Asymptomatic Carotid Stenosis Embolus Detection (ASED) Study such that half were previously ES-positive and half ES-negative with 6-monthly 60-min TCD monitoring. All underwent bilateral TCD monitoring for two 12-h sessions separated by 24 h. ES detection rates were calculated using 6 and 4-h intervals from midnight and effective TCD monitoring time. Results: Ten subjects (8 male, mean age 79.5 years) were monitored. Over 24 h, 5/10 study arteries with 60–99% asymptomatic carotid stenosis were ES-positive (range 1–28 ES/artery, 56 total ES from 177.9 total effective monitoring hours). The remaining five study arteries and all eight successfully monitored contralateral arteries were ES-negative. Using 6-h intervals the mean ES detection rate peaked at 0600-midday (0.64/h) and was lowest 1800-midnight (0.09/h) with an incidence rate ratio of 7.26 (95% CI 2.52–28.64, P ≤ 0.001). Using 4-h intervals the mean ES detection rate peaked at 0800-midday (0.64/h) and was lowest midnight-0400 (0.12/h) with an incidence rate ratio of 5.51 (95% CI 1.78–22.67, P = 0.001). Conclusions: Embolism associated with asymptomatic carotid stenosis shows circadian variation with highest rates 4–6 h before midday. This corresponds with peak circadian incidence of stroke and other vascular complications. These and ASED Study results show that monitoring frequency, duration, and time of day are important in ES detection. © Copyright © 2019 Abbott, Merican, Pearce, Juric, Worsnop, Foster and Chambers

Asymptomatic Carotid Stenosis Is Associated With Circadian and Other Variability in Embolus Detection

Background and Purpose: Variability in transcranial Doppler (TCD) detection of embolic signals (ES) is important for risk stratification. We tested the effect of time of day on ES associated with 60–99% asymptomatic carotid stenosis.Materials and Methods: Subjects were from the Asymptomatic Carotid Stenosis Embolus Detection (ASED) Study such that half were previously ES-positive and half ES-negative with 6-monthly 60-min TCD monitoring. All underwent bilateral TCD monitoring for two 12-h sessions separated by 24 h. ES detection rates were calculated using 6 and 4-h intervals from midnight and effective TCD monitoring time.Results: Ten subjects (8 male, mean age 79.5 years) were monitored. Over 24 h, 5/10 study arteries with 60–99% asymptomatic carotid stenosis were ES-positive (range 1–28 ES/artery, 56 total ES from 177.9 total effective monitoring hours). The remaining five study arteries and all eight successfully monitored contralateral arteries were ES-negative. Using 6-h intervals the mean ES detection rate peaked at 0600-midday (0.64/h) and was lowest 1800-midnight (0.09/h) with an incidence rate ratio of 7.26 (95% CI 2.52–28.64, P ≤ 0.001). Using 4-h intervals the mean ES detection rate peaked at 0800-midday (0.64/h) and was lowest midnight-0400 (0.12/h) with an incidence rate ratio of 5.51 (95% CI 1.78–22.67, P = 0.001).Conclusions: Embolism associated with asymptomatic carotid stenosis shows circadian variation with highest rates 4–6 h before midday. This corresponds with peak circadian incidence of stroke and other vascular complications. These and ASED Study results show that monitoring frequency, duration, and time of day are important in ES detection

Chemical Evolution of Atmospheric Organic Carbon over Multiple Generations of Oxidation

The evolution of atmospheric organic carbon (OC) as it undergoes oxidation has a controlling influence on concentrations of key atmospheric species, including particulate matter, ozone, and oxidants. However, the full characterization of OC over hours to days of atmospheric processing has been stymied by its extreme chemical complexity. Here we study the multigenerational oxidation of -pinene in the laboratory, characterizing products with several state-of-the-art analytical techniques. While quantification of some early-generation products remains elusive, full carbon closure is achieved (within uncertainty) by the end of the experiments. This enables new insights into the effects of oxidation on OC properties (volatility, oxidation state, and reactivity), and the atmospheric lifecycle of OC. Following an initial period characterized by functionalization reactions and particle growth, fragmentation reactions dominate, forming smaller species. After approximately one day of atmospheric aging, most carbon is sequestered in two long-lived reservoirs, volatile oxidized gases and low-volatility particulate matter

Formation of Highly Oxygenated Organic Molecules from alpha-Pinene Ozonolysis : Chemical Characteristics, Mechanism, and Kinetic Model Development

Terpenes are emitted by vegetation, and their oxidation in the atmosphere is an important source of secondary organic aerosol (SOA). A part of this oxidation can proceed through an autoxidation process, yielding highly oxygenated organic molecules (HOMs) with low saturation vapor pressure. They can therefore contribute, even in the absence of sulfuric acid, to new particle formation (NPF). The understanding of the autoxidation mechanism and its kinetics is still far from complete. Here, we present a mechanistic and kinetic analysis of mass spectrometry data from α-pinene (AP) ozonolysis experiments performed during the CLOUD 8 campaign at CERN. We grouped HOMs in classes according to their identified chemical composition and investigated the relative changes of these groups and their components as a function of the reagent concentration. We determined reaction rate constants for the different HOM peroxy radical reaction pathways. The accretion reaction between HOM peroxy radicals was found to be extremely fast. We developed a pseudo-mechanism for HOM formation and added it to the AP oxidation scheme of the Master Chemical Mechanism (MCM). With this extended model, the observed concentrations and trends in HOM formation were successfully simulated.Peer reviewe

Observation of viscosity transition in alpha-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of alpha-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35aEuro-% at -10aEuro-A degrees C and 80aEuro-% at -38aEuro-A degrees C, confirming previous calculations of the viscosity-transition conditions. Consequently, alpha-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.Peer reviewe

Observation of viscosity transition in α-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere

Molecular characterization of ultrafine particles using extractive electrospray time-of-flight mass spectrometry

Publisher Copyright: © 2021 The Author(s).Aerosol particles negatively affect human health while also having climatic relevance due to, for example, their ability to act as cloud condensation nuclei. Ultrafine particles (diameter Dp < 100 nm) typically comprise the largest fraction of the total number concentration, however, their chemical characterization is difficult because of their low mass. Using an extractive electrospray time-of-flight mass spectrometer (EESI-TOF), we characterize the molecular composition of freshly nucleated particles from naphthalene and b-caryophyllene oxidation products at the CLOUD chamber at CERN. We perform a detailed intercomparison of the organic aerosol chemical composition measured by the EESI-TOF and an iodide adduct chemical ionization mass spectrometer equipped with a filter inlet for gases and aerosols (FIGAERO-I-CIMS). We also use an aerosol growth model based on the condensation of organic vapors to show that the chemical composition measured by the EESI-TOF is consistent with the expected condensed oxidation products. This agreement could be further improved by constraining the EESI-TOF compound-specific sensitivity or considering condensed-phase processes. Our results show that the EESI-TOF can obtain the chemical composition of particles as small as 20 nm in diameter with mass loadings as low as hundreds of ng m_3 in real time. This was until now difficult to achieve, as other online instruments are often limited by size cutoffs, ionization/thermal fragmentation and/or semicontinuous sampling. Using real-time simultaneous gas- and particle-phase data, we discuss the condensation of naphthalene oxidation products on a molecular level.Peer reviewe

Influence of temperature on the molecular composition of ions and charged clusters during pure biogenic nucleation

It was recently shown by the CERN CLOUD experiment that biogenic highly oxygenated molecules (HOMs) form particles under atmospheric conditions in the absence of sulfuric acid, where ions enhance the nucleation rate by 1-2 orders of magnitude. The biogenic HOMs were produced from ozonolysis of alpha-pinene at 5 degrees C. Here we extend this study to compare the molecular composition of positive and negative HOM clusters measured with atmospheric pressure interface time-of-flight mass spectrometers (APi-TOFs), at three different temperatures (25, 5 and -25 degrees C). Most negative HOM clusters include a nitrate (NO3-) ion, and the spectra are similar to those seen in the nighttime boreal forest. On the other hand, most positive HOM clusters include an ammonium (NH4+) 4) ion, and the spectra are characterized by mass bands that differ in their molecular weight by similar to 20 C atoms, corresponding to HOM dimers. At lower temperatures the average oxygen to carbon (O : C) ratio of the HOM clusters decreases for both polarities, reflecting an overall reduction of HOM formation with decreasing temperature. This indicates a decrease in the rate of autoxidation with temperature due to a rather high activation energy as has previously been determined by quantum chemical calculations. Furthermore, at the lowest temperature (-25 degrees C), the presence of C-30 clusters shows that HOM monomers start to contribute to the nucleation of positive clusters. These experimental findings are supported by quantum chemical calculations of the binding energies of representative neutral and charged clusters.Peer reviewe

Role of sesquiterpenes in biogenic new particle formation

Biogenic vapors form new particles in the atmosphere, affecting global climate. The contributions of monoterpenes and isoprene to new particle formation (NPF) have been extensively studied. However, sesquiterpenes have received little attention despite a potentially important role due to their high molecular weight. Via chamber experiments performed under atmospheric conditions, we report biogenic NPF resulting from the oxidation of pure mixtures of β-caryophyllene, α-pinene, and isoprene, which produces oxygenated compounds over a wide range of volatilities. We find that a class of vapors termed ultralow-volatility organic compounds (ULVOCs) are highly efficient nucleators and quantitatively determine NPF efficiency. When compared with a mixture of isoprene and monoterpene alone, adding only 2% sesquiterpene increases the ULVOC yield and doubles the formation rate. Thus, sesquiterpene emissions need to be included in assessments of global aerosol concentrations in pristine climates where biogenic NPF is expected to be a major source of cloud condensation nuclei

The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source

Iodine is a reactive trace element in atmospheric chemistry that destroys ozone and nucleates particles. Iodine emissions have tripled since 1950 and are projected to keep increasing with rising O-3 surface concentrations. Although iodic acid (HIO3) is widespread and forms particles more efficiently than sulfuric acid, its gas-phase formation mechanism remains unresolved. Here, in CLOUD atmospheric simulation chamber experiments that generate iodine radicals at atmospherically relevant rates, we show that iodooxy hypoiodite, IOIO, is efficiently converted into HIO3 via reactions (R1) IOIO + O-3 -> IOIO4 and (R2) IOIO4 + H2O -> HIO3 + HOI + O-(1)(2). The laboratory-derived reaction rate coefficients are corroborated by theory and shown to explain field observations of daytime HIO3 in the remote lower free troposphere. The mechanism provides a missing link between iodine sources and particle formation. Because particulate iodate is readily reduced, recycling iodine back into the gas phase, our results suggest a catalytic role of iodine in aerosol formation.Peer reviewe