Atmos.Meas.Tech. discussions

Measurement of ammonia, amines and iodine compounds using protonated water cluster chemical ionization mass spectrometry
Joschka Pfeifer, Mario Simon, Martin Heinritzi, Felix Piel, Lena Weitz, Dongyu Wang, Manuel Granzin, Tatjana Müller, Steffen Bräkling, Jasper Kirkby, Joachim Curtius, and Andreas Kürten
Atmos. Meas. Tech., 13, 2501–2522, https://doi.org/10.5194/amt-13-2501-2020, 2020
Ammonia is an important atmospheric trace gas that affects secondary aerosol formation and, together with sulfuric acid, the formation of new particles. A measurement technique is presented that uses high-resolution mass spectrometry and protonated water clusters for the ultrasensitive detection of ammonia at single-digit parts per trillion by volume levels. The instrument is further capable of measuring amines and a suite of iodine compounds at sub-parts per trillion by volume levels.

A low-activity ion source for measurement of atmospheric gases by chemical ionization mass spectrometry
Young Ro Lee, Yi Ji, David J. Tanner, and L. Gregory Huey
Atmos. Meas. Tech., 13, 2473–2480, https://doi.org/10.5194/amt-13-2473-2020, 2020
In this work we show how to construct a radioactive ion source for a chemical ionization mass spectrometer (CIMS) from commercially available components. The source is low activity and can be shipped with a minimum of complications. This facilitates the deployment of CIMS to measure atmospheric pollutants at remote ground sites.

Characterization of anthropogenic organic aerosols by TOF-ACSM with the new capture vaporizer
Yan Zheng, Xi Cheng, Keren Liao, Yaowei Li, Yong Jie Li, Ru-Jin Huang, Weiwei Hu, Ying Liu, Tong Zhu, Shiyi Chen, Limin Zeng, Douglas R. Worsnop, and Qi Chen
Atmos. Meas. Tech., 13, 2457–2472, https://doi.org/10.5194/amt-13-2457-2020, 2020
This paper provides important information to help researchers to understand the mass quantification and source apportionment by Aerodyne aerosol mass spectrometers.

MICRU background map and effective cloud fraction algorithms designed for UV/vis satellite instruments with large viewing angles
Holger Sihler, Steffen Beirle, Steffen Dörner, Marloes Gutenstein-Penning de Vries, Christoph Hörmann, Christian Borger, Simon Warnach, and Thomas Wagner
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-182,2020
Preprint under review for AMT (discussion: open, 0 comments)
MICRU is an algorithm for the retrieval of effective cloud fractions (CF) from satellite measurements. CF describe the amount of clouds, which have a significant impact on the vertical sensitivity profile of trace-gases like NO2 and HCHO. MICRU retrieves small CF with an accuracy of 0.04 over the entire satellite swath. It features an empirical surface reflectivity model accounting for physical anisotropy (BRDF, sun glitter) and instrumental effects. MICRU is also applicable to imager data.

A new OCO-2 cloud flagging and rapid retrieval of marine boundary layer cloud properties
Mark Richardson, Matthew D. Lebsock, James McDuffie, and Graeme L. Stephens
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-140,2020
Preprint under review for AMT (discussion: open, 0 comments)
We previously combined data from a lidar on the CALIPSO satellite and measurements of reflected sunlight from the OCO-2 satellite to get new information about low clouds over oceans. The satellites are no longer formation flying, so this work is a step towards getting unique new information about these clouds using OCO-2 data only. We show we can rapidly and accurately identify liquid oceanic clouds and obtain their height better than a widely-used passive sensor.

An intercomparison of CH3O2 measurements by fluorescence assay by gas expansion and cavity ring-down spectroscopy within HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry)
Lavinia Onel, Alexander Brennan, Michele Gianella, James Hooper, Nicole Ng, Gus Hancock, Lisa Whalley, Paul W. Seakins, Grant A. D. Ritchie, and Dwayne E. Heard
Atmos. Meas. Tech., 13, 2441–2456, https://doi.org/10.5194/amt-13-2441-2020, 2020

Simultaneous measurements of CH3O2 radical concentrations have been performed using two different methods in the Leeds HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) chamber at 295 K and in 80 mbar of a mixture of 3:1 He∕O2 and 100 or 1000 mbar of synthetic air. The first detection method consisted of the indirect detection of CH3O2 using the conversion of CH3O2 into CH3O by excess NO with subsequent detection of CH3O by fluorescence assay by gas expansion (FAGE). The FAGE instrument was calibrated for CH3O2 in two ways. In the first method, a known concentration of CH3O2 was generated using the 185 nm photolysis of water vapour in synthetic air at atmospheric pressure followed by the conversion of the generated OH radicals to CH3O2 by reaction with CH4∕O2. This calibration can be used for experiments performed in HIRAC at 1000 mbar in air. In the second method, calibration was achieved by generating a near steady state of CH3O2 and then switching off the photolysis lamps within HIRAC and monitoring the subsequent decay of CH3O2, which was controlled via its self-reaction, and analysing the decay using second-order kinetics. This calibration could be used for experiments performed at all pressures. In the second detection method, CH3O2 was measured directly using cavity ring-down spectroscopy (CRDS) using the absorption at 7487.98 cm−1 in the A←X (ν12) band with the optical path along the ∼1.4 m chamber diameter. Analysis of the second-order kinetic decays of CH3O2 by self-reaction monitored by CRDS has been used for the determination of the CH3O2 absorption cross section at 7487.98 cm−1, both at 100 mbar of air and at 80 mbar of a 3:1 He∕O2 mixture, from which σCH3O2=(1.49±0.19)×10-20 cm2 molecule−1 was determined for both pressures. The absorption spectrum of CH3O2 between 7486 and 7491 cm−1 did not change shape when the total pressure was increased to 1000 mbar, from which we determined that σCH3O2 is independent of pressure over the pressure range 100–1000 mbar in air. CH3O2 was generated in HIRAC using either the photolysis of Cl2 with UV black lamps in the presence of CH4 and O2 or the photolysis of acetone at 254 nm in the presence of O2. At 1000 mbar of synthetic air the correlation plot of [CH3O2]FAGE against [CH3O2]CRDS gave a gradient of 1.09±0.06. At 100 mbar of synthetic air the FAGE–CRDS correlation plot had a gradient of 0.95±0.024, and at 80 mbar of 3:1 He∕O2 mixture the correlation plot gradient was 1.03±0.05. These results provide a validation of the FAGE method to determine concentrations of CH3O2.

Laboratory evaluation of particle-size selectivity of optical low-cost particulate matter sensors
Joel Kuula, Timo Mäkelä, Minna Aurela, Kimmo Teinilä, Samu Varjonen, Óscar González, and Hilkka Timonen
Atmos. Meas. Tech., 13, 2413–2423, https://doi.org/10.5194/amt-13-2413-2020, 2020
Particle-size-dependent detection ranges of low-cost particulate matter sensors were evaluated in a laboratory experiment. Six different sensor models were evaluated altogether. The results showed that none of the sensor models adhered to the technical specifications provided by the manufacturers, and thus a high risk of sensor misuse is posed. It is paramount that the limitations regarding the particle size discrimination of low-cost sensors are acknowledged properly.

First validation of Aeolus wind observations by airborne Doppler wind lidar measurements
Benjamin Witschas, Christian Lemmerz, Alexander Geiß, Oliver Lux, Uwe Marksteiner, Stephan Rahm, Oliver Reitebuch, and Fabian Weiler
Atmos. Meas. Tech., 13, 2381–2396, https://doi.org/10.5194/amt-13-2381-2020, 2020
Aeolus, the first ever wind lidar in space, has been providing wind profiles on a global scale since its launch. In order to validate the quality of Aeolus wind observations, the German Aerospace Center (DLR) recently performed two airborne campaigns over central Europe deploying two different Doppler wind lidars. A total of 10 satellite underflights were performed and used to validate the early-stage wind data product of Aeolus by means of collocated airborne wind lidar observations.

Nitrate radical generation via continuous generation of dinitrogen pentoxide in a laminar flow reactor coupled to an oxidation flow reactor
Andrew T. Lambe, Ezra C. Wood, Jordan E. Krechmer, Francesca Majluf, Leah R. Williams, Philip L. Croteau, Manuela Cirtog, Anaïs Féron, Jean-Eudes Petit, Alexandre Albinet, Jose L. Jimenez, and Zhe Peng
Atmos. Meas. Tech., 13, 2397–2411, https://doi.org/10.5194/amt-13-2397-2020, 2020
We present a new method to continuously generate N2O5 in the gas phase that is injected into a reactor where it decomposes to generate nitrate radicals (NO3). To assess the applicability of the method towards different chemical systems, we present experimental and model characterization of the integrated NO3 exposure and other metrics as a function of operating conditions. We demonstrate the method by characterizing secondary organic aerosol particles generated from the β-pinene + NO3 reaction.

Single-photon laser-induced fluorescence detection of nitric oxide at sub-parts-per-trillion mixing ratios
Andrew W. Rollins, Pamela S. Rickly, Ru-Shan Gao, Thomas B. Ryerson, Steven S. Brown, Jeff Peischl, and Ilann Bourgeois
Atmos. Meas. Tech., 13, 2425–2439, https://doi.org/10.5194/amt-13-2425-2020, 2020
Nitric oxide (NO) is a key atmospheric constituent controlling atmospheric oxidation chemistry and tropospheric ozone formation. Existing instrumentation capable of quantifying NO at very low mixing ratios is uncommon and typically relies on chemiluminescence. We describe and demonstrate a new laser-based technique (LIF) with significant practical and technical advantages to CL. This technique is expected to allow for advances in understanding of atmospheric radical chemistry.

Mind the gap – Part 1: Accurately locating warm marine boundary layer clouds and precipitation using spaceborne radars
Katia Lamer, Pavlos Kollias, Alessandro Battaglia, and Simon Preval
Atmos. Meas. Tech., 13, 2363–2379, https://doi.org/10.5194/amt-13-2363-2020, 2020
According to ground-based radar observations, 50 % of liquid low-level clouds over the Atlantic extend below 1.2 km and are thinner than 400 m, thus limiting their detection from space. Using an emulator, we estimate that a 250 m resolution radar would capture cloud base better than the CloudSat radar which misses about 52 %. The more sensitive EarthCARE radar is expected to capture cloud cover but stretch cloud. This calls for the operation of interlaced pulse modes for future space missions.

Microwave and submillimeter wave scattering of oriented ice particles
Manfred Brath, Robin Ekelund, Patrick Eriksson, Oliver Lemke, and Stefan A. Buehler
Atmos. Meas. Tech., 13, 2309–2333, https://doi.org/10.5194/amt-13-2309-2020, 2020
Microwave dual-polarization observations consistently show that larger atmospheric ice particles tend to have a preferred orientation. We provide a publicly available database of microwave and submillimeter wave scattering properties of oriented ice particles based on discrete dipole approximation scattering calculations. Detailed radiative transfer simulations, recreating observed polarization patterns, are additionally presented in this study.

Atmospheric observations of the water vapour continuum in the near-infrared windows between 2500 and 6600 cm−1
Jonathan Elsey, Marc D. Coleman, Tom D. Gardiner, Kaah P. Menang, and Keith P. Shine
Atmos. Meas. Tech., 13, 2335–2361, https://doi.org/10.5194/amt-13-2335-2020, 2020
Water vapour is an important component in trying to understand the flows of energy between the Sun and Earth, since it is opaque to radiation emitted by both the surface and the Sun. In this paper, we study how it absorbs sunlight by way of its continuum, a property which is poorly understood and with few measurements. Our results indicate that this continuum absorption may be more significant than previously thought, potentially impacting satellite observations and climate studies.

Vertical wind profiling from the troposphere to the lower mesosphere based on high-resolution heterodyne near-infrared spectroradiometry
Alexander V. Rodin, Dmitry V. Churbanov, Sergei G. Zenevich, Artem Y. Klimchuk, Vladimir M. Semenov, Maxim V. Spiridonov, and Iskander S. Gazizov
Atmos. Meas. Tech., 13, 2299–2308, https://doi.org/10.5194/amt-13-2299-2020, 2020
The paper presents a new technique in remote wind measurements that may potentially complement conventional aerological observations and eventually greatly improve our knowledge about our climate system, especially concerning processes related to troposphere–stratosphere coupling. The technique may be implemented at relatively low cost in various applications from meteorological observation posts to remote sensing spacecraft.

TROPOMI Aerosol Products: Evaluation and Observations of Synoptic Scale Carbonaceous Aerosol Plumes during 2018–2020
Omar Torres, Hiren Jethva, Changwoo Ahn, Glen Jaross, and Diego G. Loyola
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-124,2020
Preprint under review for AMT (discussion: open, 0 comments)
TROPOMI measures the amount of small suspended particles (aerosols). We describe initial results of aerosol measurements using a NASA algorithm that retrieves the UV Aerosol Index, as well as Aerosol Optical Depth and Single Scattering Albedo. An evaluation of derived products using sun-photometer observations shows close agreement. We also use these results to discuss important biomass burning and wildfire events around the world that got the attention of scientists and news media alike.

Improvement of numerical weather prediction model analysis during fog conditions through the assimilation of ground-based microwave radiometer observations: a 1D-Var study
Pauline Martinet, Domenico Cimini, Frédéric Burnet, Benjamin Ménétrier, Yann Michel, and Vinciane Unger
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-166,2020
Preprint under review for AMT (discussion: open, 0 comments)
Each year large human and economical losses are due to fog episodes. However, fog forecasts remain quite inaccurate partly due to a lack of observations in the atmospheric boundary layer. The benefit of ground-based microwave radiometers has been investigated and has demonstrated their capability of significantly improving the initial state of temperature and liquid water content profiles in current numerical weather prediction model paving the way for improved fog forecasts in the future.

Stratospheric Extinction Profiles from SCIAMACHY Solar Occultation
Stefan Noël, Klaus Bramstedt, Alexei Rozanov, Elizaveta Malinina, Heinrich Bovensmann, and John P. Burrows
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-113,2020
Preprint under review for AMT (discussion: open, 0 comments)
A new approach to derive stratospheric aerosol extinction profiles between 15 and 30 km from SCIAMACHY solar occultation measurements is presented. Except for some oscillating features the results for 452, 525 and 750 nm agree well with collocated SAGE II and SCIAMACHY limb data products. Volcanic eruptions and polar stratospheric clouds can be identified in the time series. Linear changes of extinction between 2003 and 2011 reach 20–30 % per year, mainly due to volcanic eruptions after 2006.

Quantifying the impact of aerosol scattering on the retrieval of methane from airborne remote sensing measurements
Yunxia Huang, Vijay Natraj, Zhaocheng Zeng, and Yuk L. Yung
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-51,2020
Preprint under review for AMT (discussion: open, 0 comments)
As a greenhouse gas with strong global warming potential, atmospheric methane emissions have attracted a great deal of attention. However, accurate assessment of these emissions is challenging in the presence of atmospheric particulates called aerosols. We quantify the aerosol impact on methane quantification from airborne measurements using two techniques, one that has traditionally been used by the imaging spectroscopy community and the other commonly employed in trace gas remote sensing.

Generalized Canonical Transform method for radio occultation sounding with improved retrieval in the presence of horizontal gradients
Michael Gorbunov, Gottfried Kirchengast, and Kent B. Lauritsen
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-147,2020
Preprint under review for AMT (discussion: open, 0 comments)
By now, the Canonical Transform (CT) approach to the processing of Radio Occultation (RO) observations is widely used. For the spherically symmetric atmosphere, the applicability of this method can be strictly proven. However, in the presence of horizontal gradients, this approach may not work. Here we introduce a generalization of the CT method in order to reduce the errors due to horizontal gradients.

A machine-learning-based cloud detection and thermodynamic-phase classification algorithm using passive spectral observations
Chenxi Wang, Steven Platnick, Kerry Meyer, Zhibo Zhang, and Yaping Zhou
Atmos. Meas. Tech., 13, 2257–2277, https://doi.org/10.5194/amt-13-2257-2020, 2020
A machine-learning (ML)-based approach that can be used for cloud mask and phase detection is developed. An all-day model that uses infrared (IR) observations and a daytime model that uses shortwave and IR observations from a passive instrument are trained separately for different surface types. The training datasets are selected by using reference pixel types from collocated space lidar. The ML approach is validated carefully and the overall performance is better than traditional methods.