Atmos.Meas.Tech. discussions

Characterization of a Non-Thermal Plasma Source for the Use as a Mass Spec Calibration Tool and Non-Radioactive Aerosol Charger
Christian Tauber, David Schmoll, Johannes Gruenwald, Sophia Brilke, Peter Josef Wlasits, Paul Martin Winkler, and Daniela Wimmer
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-54,2020
Preprint under review for AMT (discussion: open, 0 comments)
In this paper we show that a commercially available plasma charger with nitrogen as working gas can enhance the charging probability for sub-10 nm particles. In addition, the charger ion mobilities and the chemical composition have been examined using an atmospheric pressure interface – time-of-flight mass spectrometer (APi-TOF MS) and comparison of the experimental results revealed that the generated neutralizer ions are not dependent on the charging mechanism.

Estimating raindrop size distributions using microwave link measurements: potential and limitations
Thomas C. van Leth, Hidde Leijnse, Aart Overeem, and Remko Uijlenhoet
Atmos. Meas. Tech., 13, 1797–1815, https://doi.org/10.5194/amt-13-1797-2020, 2020
We present a method of using collocated microwave link instruments to estimate the average size distribution of raindrops along a path of several kilometers. Our method is validated using simulated fields as well as five laser disdrometers installed along a path. We also present preliminary results from an experimental setup measuring at 26 and 38 GHz along a 2.2 km path. We show that a retrieval on the basis of microwave links can be highly accurate, provided the base power level is stable.

Effect of OH emission on the temperature and wind measurements derived from limb-viewing observations of the 1.27 µm O2 dayglow
Kuijun Wu, Weiwei He, Yutao Feng, Yuanhui Xiong, and Faquan Li
Atmos. Meas. Tech., 13, 1817–1824, https://doi.org/10.5194/amt-13-1817-2020, 2020
The 1.27 μm O2 dayglow is well-suited for remote sensing in near-space. The main goal of this paper is to discuss the effect of OH radiance on the wind and temperature measurements derived from limb-viewing observations of the O2 dayglow. It is apparent from the simulations that the presence of OH radiance as an interfering species decreases the wind and temperature accuracy at all altitudes, but this effect can be reduced considerably by improving OH radiance knowledge.

Spatiotemporal variability of solar radiation introduced by clouds over Arctic sea ice
Carola Barrientos Velasco, Hartwig Deneke, Hannes Griesche, Patric Seifert, Ronny Engelmann, and Andreas Macke
Atmos. Meas. Tech., 13, 1757–1775, https://doi.org/10.5194/amt-13-1757-2020, 2020
In the changing Arctic, quantifying the resulting variability of incoming solar radiation is important to better elucidate the net radiative effect of clouds. As part of a multidisciplinary expedition in the central Arctic held in early summer 2017, a novel network of pyranometers was deployed over an ice floe to investigate the spatiotemporal variability of solar radiation under different sky conditions. This study presents the collected data and an analysis of the spatiotemporal variability.

A multi-axis differential optical absorption spectroscopy aerosol profile retrieval algorithm for high-altitude measurements: application to measurements at Schneefernerhaus (UFS), Germany
Zhuoru Wang, Ka Lok Chan, Klaus-Peter Heue, Adrian Doicu, Thomas Wagner, Robert Holla, and Matthias Wiegner
Atmos. Meas. Tech., 13, 1835–1866, https://doi.org/10.5194/amt-13-1835-2020, 2020
We present a new aerosol profile retrieval algorithm for MAX-DOAS measurements at high-altitude sites and applied to the MAX-DOAS measurements at UFS. The retrieval algorithm is based on a O4 DSCD lookup table which is dedicated to high-altitude MAX-DOAS measurements. The comparison of retrieved aerosol optical depths (AODs) to sun photometer observations shows good agreement with a correlation coefficient (R) of 0.733 and 0.798 at 360 and 477 nm, respectively.

Comparison of optimal estimation HDO∕H2O retrievals from AIRS with ORACLES measurements
Robert L. Herman, John Worden, David Noone, Dean Henze, Kevin Bowman, Karen Cady-Pereira, Vivienne H. Payne, Susan S. Kulawik, and Dejian Fu
Atmos. Meas. Tech., 13, 1825–1834, https://doi.org/10.5194/amt-13-1825-2020, 2020
This study is the first assessment and validation of AIRS HDO / H2O retrieved by optimal estimation. Initial comparisons with in situ measurements from NASA ORACLES are promising: the small bias and consistent rms of AIRS suggest that AIRS has well-characterized HDO / H2O. This analysis opens the possibility of a new 17-year long-term data record of global tropospheric HDO / H2O measured from space.

Spatial distribution of cloud droplet size properties from Airborne Hyper-Angular Rainbow Polarimeter (AirHARP) measurements
Brent A. McBride, J. Vanderlei Martins, Henrique M. J. Barbosa, William Birmingham, and Lorraine A. Remer
Atmos. Meas. Tech., 13, 1777–1796, https://doi.org/10.5194/amt-13-1777-2020, 2020
Clouds play a large role in the way our Earth system distributes energy. The measurement of cloud droplet size distribution (DSD) is one way to connect small-scale cloud processes to scattered radiation. Our small satellite instrument, the Airborne Hyper-Angular Rainbow Polarimeter, is the first to infer DSDs over a wide spatial cloud field using polarized light. This study improves the way we interpret cloud properties and shows that high-quality science does not require a large taxpayer cost.

Discrete-wavelength DOAS NO2 slant column retrievals from OMI and TROPOMI
Cristina Ruiz Villena, Jasdeep S. Anand, Roland J. Leigh, Paul S. Monks, Claire E. Parfitt, and Joshua D. Vande Hey
Atmos. Meas. Tech., 13, 1735–1756, https://doi.org/10.5194/amt-13-1735-2020, 2020
We present a new method to derive NO2 concentrations from satellite observations that uses up to 30 times less spectral information than traditional methods. We tested the method using data from existing instruments OMI and TROPOMI and found our results agree with the reference data to 5 % and 11 %, respectively. Our method could allow for simpler instrument designs that can be used in low-cost constellations of small satellites for air quality monitoring at high spatial and temporal resolution.

Estimates of lightning NOx production based on high-resolution OMI NO2 retrievals over the continental US
Xin Zhang, Yan Yin, Ronald van der A, Jeff L. Lapierre, Qian Chen, Xiang Kuang, Shuqi Yan, Jinghua Chen, Chuan He, and Rulin Shi
Atmos. Meas. Tech., 13, 1709–1734, https://doi.org/10.5194/amt-13-1709-2020, 2020
Lightning NOx has a strong impact on ozone and the hydroxyl radical production. However, the production efficiency of lightning NOx is still quite uncertain. This work develops the algorithm of estimating lightning NOx for both clean and polluted regions and evaluates the sensitivity of estimates to the model setting of lightning NO. Results reveal that our method reduces the sensitivity to the background NO2 and includes much of the below-cloud LNO2.

Evaluation and calibration of a low-cost particle sensor in ambient conditions using machine-learning methods
Minxing Si, Ying Xiong, Shan Du, and Ke Du
Atmos. Meas. Tech., 13, 1693–1707, https://doi.org/10.5194/amt-13-1693-2020, 2020
The study evaluated the performance of a low-cost PM sensor in ambient conditions and calibrated its readings using simple linear regression (SLR), multiple linear regression (MLR), and two more powerful machine-learning algorithms with random search techniques for the best model architectures. The two machine-learning algorithms are XGBoost and a feedforward neural network (NN).

Retrieval and evaluation of tropospheric aerosol extinction profiles using MAX-DOAS measurements over Athens, Greece
Myrto Gratsea, Tim Bösch, Panos Kokkalis, Andreas Richter, Mihalis Vrekoussis, Stelios Kazadzis, Alexandra Tsekeri, Alexandros Papayannis, Maria Mylonaki, Vassilis Amiridis, Nikos Mihalopoulos, and Evangelos Gerasopoulos
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-100,2020
Preprint under review for AMT (discussion: open, 0 comments)

In this study, we report on the retrieval of aerosol extinction profiles from ground-based scattered sunlight multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, carried out at Athens, Greece. It is the first time that aerosol profiles are retrieved from MAX-DOAS measurements in Athens. The reported aerosol vertical distributions at 477 nm are derived from the oxygen dimer (O4) differential slant column density observations at different elevation angles by applying the BOREAS retrieval algorithm. Four case studies have been selected for validation purposes; the retrieved aerosol profiles and the corresponding aerosol optical depths (AODs) from the MAX-DOAS are compared with lidar extinction profiles and with sun photometric measurements (AERONET observations), respectively. Despite the different approach of each method regarding the retrieval of the aerosol information, the comparison with the lidar measurements at 532 nm reveals a very good agreement in terms of vertical distribution, with r > 0.85 in all cases. The AODs from the MAX-DOAS and the sun-photometer (the latter at 500 nm) show a satisfactory correlation (with r ≈ 0.6 in three out of the four cases). The comparison indicates that the MAX-DOAS systematically underestimates the AOD in the cases of large particles (small Ångström exponent) and for measurements at small relative azimuthal angles between the viewing direction and the Sun. Better agreement is achieved in the morning, at large relative azimuthal angles. Overall, the aerosol profiles retrieved from MAX-DOAS measurements are of good quality; thus, new perspectives are opened up for assessing urban aerosol pollution on a long term-basis in Athens from continuous and uninterrupted MAX-DOAS measurements.

Mixing height derivation from aerosol lidar using machine learning: KABL and ADABL algorithms
Thomas Rieutord, Sylvain Aubert, and Tiago Machado
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-78,2020
Preprint under review for AMT (discussion: open, 0 comments)
This article describes two methods to estimate the height of the very first layer of atmosphere. It is measured with aerosol lidars and the two new methods are based on machine learning. Both are open source and under free license. A sensitivity analysis and a 2-years evaluation against meteorological balloons were carried out. One method has a good agreement with balloons but is limited by training and the other has less good agreement with balloons but is more flexible.

A compact QCL spectrometer for mobile, high-precision methane sensing aboard drones
Béla Tuzson, Manuel Graf, Jonas Ravelid, Philipp Scheidegger, André Kupferschmid, Herbert Looser, Randulph Paulo Morales, and Lukas Emmenegger
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-102,2020
Preprint under review for AMT (discussion: open, 0 comments)
We describe a lightweight (2 kg) mid-IR laser spectrometer for airborne, in situ atmospheric methane (CH4) measurements. The instrument, based on an open-path circular multipass cell, provides fast response (1 Hz) and sub-ppb precision. It can easily be mounted on a drone, giving access to highly resolved 4 D (spatial and temporal) data. The performance was assessed during field deployments involving artificial CH4 sources and vertical concentration gradients in the PBL.

Surface flux estimates derived from UAS-based mole fraction measurements by means of a nocturnal boundary layer budget approach
Martin Kunz, Jost V. Lavric, Rainer Gasche, Christoph Gerbig, Richard H. Grant, Frank-Thomas Koch, Marcus Schumacher, Benjamin Wolf, and Matthias Zeeman
Atmos. Meas. Tech., 13, 1671–1692, https://doi.org/10.5194/amt-13-1671-2020, 2020
The nocturnal boundary layer (NBL) budget method enables the quantification of gas fluxes between ecosystems and the atmosphere under nocturnal stable stratification, a condition under which standard approaches struggle. However, up to now the application of the NBL method has been limited by difficulties in obtaining the required measurements. We show how an unmanned aircraft system (UAS) equipped with a carbon dioxide analyser can make this method more accessible.

A new method to correct the ECC ozone sonde time response and its implications for “background current” and pump efficiency
Holger Vömel, Herman G. J. Smit, David Tarasick, Bryan Johnson, Samuel J. Oltmans, Henry Selkirk, Anne M. Thompson, Ryan M. Stauffer, Jacquelyn C. Witte, Jonathan Davies, Roeland van Malderen, Gary A. Morris, Tatsumi Nakano, and Rene Stübi
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-62,2020
Preprint under review for AMT (discussion: open, 0 comments)
The time response of Electrochemical Concentration Cell (ECC) ozone sondes points to at least two distinct reaction pathways with time constants of approximately 20 s and 25 min. Properly considering these time constants eliminates the need for a poorly defined "background" and allows reducing ad-hoc corrections based on laboratory tests. This reduces the uncertainty of ECC ozone sonde measurements throughout the profile and especially in regions of low ozone and strong gradients of ozone.

In-orbit Earth reflectance validation of TROPOMI on board the Sentinel-5 Precursor satellite
Lieuwe G. Tilstra, Martin de Graaf, Ping Wang, and Piet Stammes
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-98,2020
Preprint under review for AMT (discussion: open, 0 comments)
The goal of the study was to determine the accuracy of the radiometric calibration of the TROPOMI instrument on board the Sentinel-5 Precursor satellite in-flight. The Earth reflectances were compared to radiative transfer calculations. We report calibration accuracies and errors for 21 selected wavelength bands between 328 and 2314 nm, located in TROPOMI spectral bands 3–7. The reported numbers can be used to perform corrections that will benefit the retrievals of many atmospheric properties.

A compact Incoherent Broadband Cavity Enhanced Absorption Spectrometer (IBBCEAS) for trace detection of nitrogen oxides, iodine oxide and glyoxal at sub-ppb levels for field application
Albane Barbero, Camille Blouzon, Joël Savarino, Nicolas Caillon, Aurélien Dommergue, and Roberto Grilli
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-104,2020
Preprint under review for AMT (discussion: open, 0 comments)
In this manuscript, we present a compact, affordable and robust instrument for in situ measurements of different trace gases: NOx, IO, CHOCHO and O3 with very low detection limits. The device weights 15 kg and has a total electrical power consumption < 300 W. Its detection limits are very low making the instrument suitable to address different questions such as better constraint the oxidative capacity of the atmosphere and study the chemistry of highly reactive species.

Improving GOES Advanced Baseline Imager (ABI) Aerosol Optical Depth (AOD) Retrievals using an Empirical Bias Correction Algorithm
Hai Zhang, Shobha Kondragunta, Istvan Laszlo, and Mi Zhou
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-115,2020
Preprint under review for AMT (discussion: open, 0 comments)

The Advanced Baseline Imager (ABI) on board the Geostationary Operational Environmental Satellite-R (GOES-R) series enables retrieval of aerosol optical depth (AOD) from geostationary satellites using a multi-band algorithm similar to those of polar-orbiting satellites’ sensors, such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS). Therefore, ABI AOD is expected to have accuracy and precision comparable to MODIS AOD and VIIRS AOD. However, this work demonstrates that the current version of GOES-16 (GOES-East) ABI AOD has diurnally varying biases due to errors in the land surface reflectance relationship between the bands used in the ABI AOD retrieval algorithm, which vary with respect to the Sun-satellite geometry. To reduce these biases, an empirical bias correction algorithm has been developed based on the lowest observed ABI AOD of an adjacent 30-day period and the background AOD at each time step and at each pixel. The bias correction algorithm improves the performance of ABI AOD compared to AErosol RObotic NETwork (AERONET) AOD, especially for the high and medium (top 2) quality ABI AOD. AOD data for the period August 6 to December 31, 2018 are used to validate the bias correction algorithm. For the top 2 qualities ABI AOD, after bias correction, the correlation between ABI AOD and AERONET AOD improves from 0.87 to 0.91, the mean bias improves from 0.04 to 0.00, and root mean square error (RMSE) improves from 0.09 to 0.05. These results for the bias corrected top 2 qualities ABI AOD are comparable to those of the uncorrected high-quality ABI AOD. Thus, by using the top 2 qualities of ABI AOD in conjunction with the bias correction algorithm, the area coverage of ABI AOD is substantially increased without loss of data accuracy.

An LES-based airborne Doppler lidar simulator and its application to wind profiling in inhomogeneous flow conditions
Philipp Gasch, Andreas Wieser, Julie K. Lundquist, and Norbert Kalthoff
Atmos. Meas. Tech., 13, 1609–1631, https://doi.org/10.5194/amt-13-1609-2020, 2020
We present an airborne Doppler lidar simulator (ADLS) based on high-resolution atmospheric wind fields (LES). The ADLS is used to evaluate the retrieval accuracy of airborne wind profiling under turbulent, inhomogeneous wind field conditions inside the boundary layer. With the ADLS, the error due to the violation of the wind field homogeneity assumption used for retrieval can be revealed. For the conditions considered, flow inhomogeneities exert a dominant influence on wind profiling error.

Towards objective identification and tracking of convective outflow boundaries in next-generation geostationary satellite imagery
Jason M. Apke, Kyle A. Hilburn, Steven D. Miller, and David A. Peterson
Atmos. Meas. Tech., 13, 1593–1608, https://doi.org/10.5194/amt-13-1593-2020, 2020
Objective identification of deep convection outflow boundaries (OFBs) in next-generation geostationary satellite imagery is explored here using motion derived from a tuned advanced optical flow algorithm. Motion discontinuity preservation within the derivation is found crucial for successful OFB tracking between images, which yields new meteorological data for objective systems to use. These results provide the first step towards a fully automated satellite-based OFB identification algorithm.