Absolutely calibrated Raman lidar as a reference tool in atmospheric humidity profiling

Raman lidars exploit the proportionality between the intensity of scattered by a Raman process laser radiation and the number density of the scattering molecules to derive water vapor mixing ratio profile. Water vapor/air mixing ratio is directly proportional to the ratio of the measured intensities of Raman scattering from water vapor and nitrogen molecules. The coefficient of proportionality, commonly denoted as calibration constant, depends on the instrument parameters and the spectroscopic parameters of the scattering molecule and is the primary factor defining lidar measurement accuracy. Derivation of the calibration constant using the above mentioned parameters is possible but leads to high uncertainty. Therefore, Raman lidars are calibrated against reference instruments- a radio sonde or a microwave radiometer. The accuracy of such calibration is thus defined by the accuracy of the reference instrument. Since these reference instruments have inferior, compared to the potential Raman lidar accuracy, this type of calibration impairs the lidar accuracy. A new first principle calibration method, based on the use of gravimetrically produced water vapor/air mixture will be presented. The method allows deriving the calibration constant with uncertainty lower than 0.1%, traceable to the primary standards of mass and length. Apart from the use for operational profiling, the calibrated in such a way lidar has the potential to become a reference in radio-sonde, microwave radiometer and GPS water vapor validation and/or calibration

Ozone LIDAR as an Analytical Tool in Effective Air Pollution Management: The Geneva 96 Campaign

The LIDAR (LIght Detection And Ranging) technique has developed into one of the practical high performance techniques for conducting air quality and meteorological measurements. DIfferential Absorption Lidar (DIAL) is used for measuring trace gases, including pollutants like ozone at low concentrations. Multiple wavelengths backscatter and depolarization measurements give information about particles in the atmosphere, and single wavelength lidar can be used for meteorological measurements like wind velocity and temperature. Range resolved in situ data obtained by lidar can play a significant role in our understanding of the air quality in the planetary boundary layer, particularly when applied in conjunction with air quality models. This is because DIAL can be used to measure concentrations in three dimensions in real time with a spatial resolution that corresponds well to that used in the model calculations. Thus one obtains an advantage when comparing with point measurements at or near ground level which are often perturbed by local emissions. A summary of the lidar principle is presented here, followed by different examples of vertical ozone profiles and time series obtained with a new optical layout of the EPFL-LPAS DIAL system using dual telescope detection. These data were obtained during the summer 96 field campaign in the Geneva area. Results are then compared with the mesoscale Eulerian model calculations performed in our laboratory. The overall results provide new insight into air pollution dynamics in the Geneva area and calculations are under way, using the model adjusted by the measurements, to optimize air pollution abatement strategies under certain atmospheric conditions in this part of Switzerland

Are atmospheric surface layer f lows ergodic?

The transposition of atmospheric turbulence statistics from the time domain, as conventionally sampled in field experiments, is explained by the so-called ergodic hypothesis. In micrometeorology, this hypothesis assumes that the time average of a measured flow variable represents an ensemble of independent realizations from similar meteorological states and boundary conditions. That is, the averaging duration must be sufficiently long to include a large number of independent realizations of the sampled flow variable so as to represent the ensemble. While the validity of the ergodic hypothesis for turbulence has been confirmed in laboratory experiments, and numerical simulations for idealized conditions, evidence for its validity in the atmospheric surface layer (ASL), especially for nonideal conditions, continues to defy experimental efforts. There is some urgency to make progress on this problem given the proliferation of tall tower scalar concentration networks aimed at constraining climate models yet are impacted by nonideal conditions at the land surface. Recent advancements in water vapor concentration lidar measurements that simultaneously sample spatial and temporal series in the ASL are used to investigate the validity of the ergodic hypothesis for the first time. It is shown that ergodicity is valid in a strict sense above uniform surfaces away from abrupt surface transitions. Surprisingly, ergodicity may be used to infer the ensemble concentration statistics of a composite grass-lake system using only water vapor concentration measurements collected above the sharp transition delineating the lake from the grass surface. Citation: Higgins, C. W., G. G. Katul, M. Froidevaux, V. Simeonov, and M. B. Parlange (2013), Are atmospheric surface layer flows ergodic?, Geophys. Res. Lett., 40, 3342–3346, doi:10.1002/grl.50642

Measured and Estimated Water Vapor Advection in the Atmospheric Surface Layer

The flux of water vapor due to advection is measured using high-resolution Raman lidar that was orientated horizontally across a land-lake transition. At the same time, a full surface energy balance is performed to assess the impact of scalar advection on energy budget closure. The flux of water vapor due to advection is then estimated with analytical solutions to the humidity transport equation that show excellent agreement with the field measurements. Although the magnitude of the advection was not sufficient to account for the total energy deficit for this field site, the analytical approach is used to explore situations where advection would be the dominant transport mechanism. The authors find that advection is at maximum when the measurement height is 0.036 times the distance to a land surface transition. The framework proposed in this paper can be used to predict the potential impact of advection on surface flux measurements prior to field deployment and can be used as a data analysis algorithm to calculate the flux of water vapor due to advection from field measurements

The Effect of Scale on the Applicability of Taylor’s Frozen Turbulence Hypothesis in the Atmospheric Boundary Layer

Taylor’s frozen turbulence hypothesis is the central assumption invoked in most experiments designed to investigate turbulence physics with time resolving sensors. It is also frequently used in theoretical discussions when linking Lagrangian to Eulerian flow formalisms. In this work we seek to quantify the effectiveness of Taylor’s hypothesis on the field scale using water vapour as a passive tracer. A horizontally orientated Raman lidar is used to capture the humidity field in space and time above an agricultural region in Switzerland. High resolution wind speed and direction measurements are conducted simultaneously allowing for a direct test of Taylor’s hypothesis at the field scale. Through a wavelet decomposition of the lidar humidity measurements we show that the scale of turbulent motions has a strong influence on the applicability of Taylor’s hypothesis. This dependency on scale is explained through the use of dimensional analysis.We identify a ‘persistency scale’ that can be used to quantify the effectiveness of Taylor’s hypothesis, and present the accuracy of the hypothesis as a function of this non-dimensional length scale. These results are further investigated and verified through the use of large-eddy simulations.Keywords: Humidity, Atmospheric boundary layer, Taylor’s frozen turbulence hypothesis, Raman lida

A Raman lidar to measure water vapor in the atmospheric boundary layer

A new multi-telescope scanning Raman lidar designed to measure the water vapor mixing ratio in the atmospheric boundary layer for a complete diurnal cycle with high resolution spatial (1.25 m) and temporal (1 s) resolutions is presented. The high resolution allows detailed measurements of the lower atmosphere and offers new opportunities for evaporation and boundary layer research, atmospheric profiling and visualization. This lidar utilizes a multi-telescope design that provides for an operational range with a nearly constant signal-to-noise ratio, which allows for statistical investigations of atmospheric turbulence. This new generation ground-based water vapor Raman lidar is described, and first observations from the Turbulent Atmospheric Boundary Layer Experiment (TABLE) are presented. Direct comparison with in-situ point measurements obtained during the field campaign demonstrate the ability of the lidar to reliably measure the water vapor mixing ratio. Horizontal measurements taken with time are used to determine the geometric characteristics of coherent structures. Vertical scans are used to visualize nocturnal jet features, layered structures within a stably stratified atmosphere and the internal boundary layer structure over a lake. (C) 2012 Elsevier Ltd. All rights reserved

A Raman lidar to measure water vapor in the atmospheric boundary layer

A new multi-telescope scanning Raman lidar designed to measure the water vapor mixing ratio for a complete diurnal cycle with high raw spatial (1.25 m) and temporal (1 s) resolutions is presented. The high resolution allows detailed measurements of the lower atmosphere and offers new opportunities for boundary layer research, atmospheric profiling and visualization. This lidar utilizes a multi-telescope design that provides for an operational range with a nearly constant signal-to-noise ratio, which allows for statistical investigations of atmospheric turbulence. This new generation ground-based water vapor Raman lidar is described, and first observations from the Turbulent Atmospheric Boundary Layer Experiment (TABLE) are presented. Direct comparison with in-situ point measurements obtained during the field campaign demonstrate the ability of the lidar to reliably measure the water vapor mixing ratio. Horizontal measurements taken with time are used to determine the geometric characteristics of coherent structures. Vertical scans are used to visualize nocturnal jet features, layered structures within a stably stratified atmosphere and the internal boundary layer structure over a lake.Keywords: Atmospheric Boundary Layer, Water Vapor, Raman Lida

Cabbage and fermented vegetables : From death rate heterogeneity in countries to candidates for mitigation strategies of severe COVID-19

Large differences in COVID-19 death rates exist between countries and between regions of the same country. Some very low death rate countries such as Eastern Asia, Central Europe, or the Balkans have a common feature of eating large quantities of fermented foods. Although biases exist when examining ecological studies, fermented vegetables or cabbage have been associated with low death rates in European countries. SARS-CoV-2 binds to its receptor, the angiotensin-converting enzyme 2 (ACE2). As a result of SARS-CoV-2 binding, ACE2 downregulation enhances the angiotensin II receptor type 1 (AT(1)R) axis associated with oxidative stress. This leads to insulin resistance as well as lung and endothelial damage, two severe outcomes of COVID-19. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is the most potent antioxidant in humans and can block in particular the AT(1)R axis. Cabbage contains precursors of sulforaphane, the most active natural activator of Nrf2. Fermented vegetables contain many lactobacilli, which are also potent Nrf2 activators. Three examples are: kimchi in Korea, westernized foods, and the slum paradox. It is proposed that fermented cabbage is a proof-of-concept of dietary manipulations that may enhance Nrf2-associated antioxidant effects, helpful in mitigating COVID-19 severity.Peer reviewe

Nrf2-interacting nutrients and COVID-19 : time for research to develop adaptation strategies

There are large between- and within-country variations in COVID-19 death rates. Some very low death rate settings such as Eastern Asia, Central Europe, the Balkans and Africa have a common feature of eating large quantities of fermented foods whose intake is associated with the activation of the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) anti-oxidant transcription factor. There are many Nrf2-interacting nutrients (berberine, curcumin, epigallocatechin gallate, genistein, quercetin, resveratrol, sulforaphane) that all act similarly to reduce insulin resistance, endothelial damage, lung injury and cytokine storm. They also act on the same mechanisms (mTOR: Mammalian target of rapamycin, PPAR gamma:Peroxisome proliferator-activated receptor, NF kappa B: Nuclear factor kappa B, ERK: Extracellular signal-regulated kinases and eIF2 alpha:Elongation initiation factor 2 alpha). They may as a result be important in mitigating the severity of COVID-19, acting through the endoplasmic reticulum stress or ACE-Angiotensin-II-AT(1)R axis (AT(1)R) pathway. Many Nrf2-interacting nutrients are also interacting with TRPA1 and/or TRPV1. Interestingly, geographical areas with very low COVID-19 mortality are those with the lowest prevalence of obesity (Sub-Saharan Africa and Asia). It is tempting to propose that Nrf2-interacting foods and nutrients can re-balance insulin resistance and have a significant effect on COVID-19 severity. It is therefore possible that the intake of these foods may restore an optimal natural balance for the Nrf2 pathway and may be of interest in the mitigation of COVID-19 severity

Is diet partly responsible for differences in COVID-19 death rates between and within countries?

Correction: Volume: 10 Issue: 1 Article Number: 44 DOI: 10.1186/s13601-020-00351-w Published: OCT 26 2020Reported COVID-19 deaths in Germany are relatively low as compared to many European countries. Among the several explanations proposed, an early and large testing of the population was put forward. Most current debates on COVID-19 focus on the differences among countries, but little attention has been given to regional differences and diet. The low-death rate European countries (e.g. Austria, Baltic States, Czech Republic, Finland, Norway, Poland, Slovakia) have used different quarantine and/or confinement times and methods and none have performed as many early tests as Germany. Among other factors that may be significant are the dietary habits. It seems that some foods largely used in these countries may reduce angiotensin-converting enzyme activity or are anti-oxidants. Among the many possible areas of research, it might be important to understand diet and angiotensin-converting enzyme-2 (ACE2) levels in populations with different COVID-19 death rates since dietary interventions may be of great benefit.Peer reviewe