scholarly journals Performance of an open-path near-infrared measurement system for measurements of CO<sub>2</sub> and CH<sub>4</sub> during extended field trials

2021 ◽  
Vol 14 (4) ◽  
pp. 3119-3130
Author(s):  
Nicholas M. Deutscher ◽  
Travis A. Naylor ◽  
Christopher G. R. Caldow ◽  
Hamish L. McDougall ◽  
Alex G. Carter ◽  
...  
Keyword(s):  
Near Infrared ◽  
In Situ Measurements ◽  
Point Sources ◽  
Atmospheric Composition ◽  
Small Scale ◽  
Open Path ◽  
Local Point ◽  
Extended Field ◽  
Measurement Repeatability

Abstract. Open-path measurements of atmospheric composition provide spatial averages of trace gases that are less sensitive to small-scale variations and the effects of meteorology. In this study we introduce improvements to open-path near-infrared (OP-NIR) Fourier transform spectrometer measurements of CO2 and CH4. In an extended field trial, the OP-NIR achieved measurement repeatability 6 times better for CO2 (0.28 ppm) and 10 times better for CH4 (2.1 ppb) over a 1.55 km one-way path than its predecessor. The measurement repeatability was independent of path length up to 1.55 km, the longest distance tested. Comparisons to co-located in situ measurements under well-mixed conditions characterise biases of 1.41 % for CO2 and 1.61 % for CH4 relative to in situ measurements calibrated to World Meteorological Organisation – Global Atmosphere Watch (WMO-GAW) scales. The OP-NIR measurements can detect signals due to local photosynthesis and respiration, and local point sources of CH4. The OP-NIR is well-suited for deployment in urban or rural settings to quantify atmospheric composition on kilometre scales.

scholarly journals Performance of an open-path near infrared measurement system for measurements of CO<sub>2</sub> and CH<sub>4</sub> during extended field trials

2020 ◽  
Author(s):  
Nicholas M. Deutscher ◽  
Travis A. Naylor ◽  
Christopher G. R. Caldow ◽  
Hamish L. McDougall ◽  
Alex G. Carter ◽  
...  
Keyword(s):  
Near Infrared ◽  
In Situ Measurements ◽  
Point Sources ◽  
Atmospheric Composition ◽  
Small Scale ◽  
Open Path ◽  
Local Point ◽  
Extended Field ◽  
Measurement Repeatability

Abstract. Open-path measurements of atmospheric composition provide spatial averages of trace gases that are less sensitive to small-scale variations and the effects of meteorology. In this study we introduce improvements to Open-Path Near Infrared (OP-NIR) Fourier Transform Spectrometer measurements of CO2 and CH4. In an extended field trial, the OP-NIR achieved measurement repeatability six times better for CO2 (0.26 ppm) and ten times better for CH4 (2.0 ppb) over a 1.55 km one-way path than its predecessor. The measurement repeatability was independent of pathlength up to 1.55 km, the longest distance tested. Comparisons to co-located in situ measurements under well-mixed conditions characterise biases of 2.67 % for CO2 and 2.46 % for CH4 relative to in situ measurements calibrated to World Meteorological Organisation – Global Atmosphere Watch (WMO-GAW) scales. The OP-NIR measurements can detect signals due to local photosynthesis and respiration, and local point sources of CH4. The OP-NIR is well-suited for deployment in urban or rural settings to quantify atmospheric composition on kilometre scales.

scholarly journals Long open path measurements of greenhouse gases in air using near infrared Fourier transform spectroscopy

2017 ◽  
Author(s):  
David W. T. Griffith ◽  
Denis Pöhler ◽  
Stefan Schmitt ◽  
Samuel Hammer ◽  
Sanam N. Vardag ◽  
...  
Keyword(s):  
Near Infrared ◽  
Measurement Techniques ◽  
Trace Gas ◽  
Small Scale ◽  
Gas Composition ◽  
Spatial Averaging ◽  
Mid Infrared ◽  
Open Path ◽  
Atmospheric Trace Gas

Abstract. In complex and urban environments, atmospheric trace gas composition is highly variable in time and space. Point measurement techniques for trace gases with in situ instruments are well established and accurate, but do not provide spatial averaging to compare against developing high resolution atmospheric models of composition and small scale meteorology with resolutions of the order of a kilometre. Open path measurement techniques provide path average concentrations and spatial averaging which, if sufficiently accurate, may be better suited to assessment and interpretation with such models. Open path Fourier Transform Spectroscopy (FTS) in the mid infrared region, and Differential Optical Absorption Spectroscopy (DOAS) in the UV and visible, have been used for many years for open path spectroscopic measurements of selected species in both clean air and in polluted environments. Compared to the mid infrared, near infrared instrumentation allows measurements over longer paths than mid IR FTS, for species such as greenhouse gases which are not easily accessible to DOAS. In this pilot study we present the first open path near infrared (4000–10 000 cm−1, 1.0–2.5 μm) FTS measurements of CO2, CH4, O2, H2O and HDO over a 1.5 km path in urban Heidelberg, Germany. We describe the construction of the open path FTS system, the analysis of the collected spectra, precision and accuracy of the measurements, and the results from a four-month trial measurement period in July–November 2014. The open path measurements are compared to calibrated in situ measurements made at one end of the open path. There are small but significant differences between in situ and open path measurements coincident in time which reflect local sources and sinks and the way in which they are sampled by the point and path-averaged measurements. Open path FTS may provide a valuable new tool for investigations of atmospheric trace gas composition in complex, small scale environments such as cities.

scholarly journals First ground-based Fourier transform infrared (FTIR) spectrometer observations of HFC-23 at Rikubetsu, Japan, and Syowa Station, Antarctica

2021 ◽  
Vol 14 (9) ◽  
pp. 5955-5976
Author(s):  
Masanori Takeda ◽  
Hideaki Nakajima ◽  
Isao Murata ◽  
Tomoo Nagahama ◽  
Isamu Morino ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Fourier Transform Infrared ◽  
In Situ Measurements ◽  
Atmospheric Composition ◽  
Syowa Station ◽  
Spectroscopic Parameters ◽  
Dry Air ◽  
Systematic Uncertainties ◽  
Ftir Spectrometer

Abstract. We have developed a procedure for retrieving atmospheric abundances of HFC-23 (CHF3) with a ground-based Fourier transform infrared (FTIR) spectrometer and analyzed the spectra observed at Rikubetsu, Japan (43.5∘ N, 143.8∘ E), and at Syowa Station, Antarctica (69.0∘ S, 39.6∘ E). The FTIR retrievals were carried out with the SFIT4 retrieval program, and the two spectral windows of 1138.5–1148.0 cm−1 and 1154.0–1160.0 cm−1 in the overlapping ν2 and ν5 vibrational–rotational transition bands of HFC-23 were used to avoid strong H2O absorption features. We considered O3, N2O, CH4, H2O, HDO, CFC-12 (CCl2F2), HCFC-22 (CHClF2), peroxyacetyl nitrate (PAN) (CH3C(O)OONO2), HCFC-141b (CH3CCl2F), and HCFC-142b (CH3CClF2) to be interfering species. Vertical profiles of H2O, HDO, and CH4 are preliminarily retrieved with other independent spectral windows because these profiles may induce large uncertainties in the HFC-23 retrieval. Each HFC-23 retrieval has only one piece of vertical information with sensitivity to HFC-23 in the troposphere and the lower stratosphere. Retrieval errors mainly arise from the systematic uncertainties of the spectroscopic parameters used to obtain HFC-23, H2O, HDO, and CH4 abundances. For comparison between FTIR-retrieved HFC-23 total columns and surface dry-air mole fractions provided by AGAGE (Advanced Global Atmospheric Gases Experiment), FTIR-retrieved HFC-23 dry-air column-averaged mole fractions (XHFC-23) were calculated. The FTIR-retrieved XHFC-23 values at Rikubetsu and Syowa Station have negative biases of −15 % to −20 % and −25 % compared to the AGAGE datasets, respectively. These negative biases might mainly come from systematic uncertainties of HFC-23 spectroscopic parameters. The trend of the FTIR-retrieved XHFC-23 data at Rikubetsu was derived for December to February (DJF) observations, which are considered to represent the background values when an air mass reaching Rikubetsu has the least influence by transport of HFC-23 emissions from nearby countries. The DJF trend of Rikubetsu over the 1997–2009 period is 0.810 ± 0.093 ppt yr−1 (ppt: parts per trillion), which is in good agreement with the trend derived from the annual global mean datasets of the AGAGE 12-box model for the same period (0.820 ± 0.013 ppt yr−1). The DJF trend of Rikubetsu over the 2008–2019 period is 0.928 ± 0.108 ppt yr−1, which is consistent with the trend in the AGAGE in situ measurements at Trinidad Head (41.1∘ N, 124.2∘ W) for the same period (0.994 ± 0.001 ppt yr−1). The trend of the FTIR-retrieved XHFC-23 data at Syowa Station over the 2007–2016 period is 0.819 ± 0.071 ppt yr−1, which is consistent with that derived from the AGAGE in situ measurements at Cape Grim (40.7∘ S, 144.7∘ E) for the same period (0.874 ± 0.002 ppt yr−1). Although there are systematic biases in the FTIR-retrieved XHFC-23 at both sites, these results indicate that ground-based FTIR observations have the capability to monitor the long-term trend of atmospheric HFC-23. If this FTIR measurement technique were extended to other Network for the Detection of Atmospheric Composition Change (NDACC) ground-based FTIR sites around world, the measurements reported from these sites would complement the global AGAGE observations by filling spatial and temporal gaps and may lead to improved insights about changes in regional and global emissions of HFC-23 and its role in global warming.

Modelling rain heterogeneities within an urban neighbourhood

2021 ◽  
Author(s):  
Karolin S. Ferner ◽  
K. Heinke Schlünzen ◽  
Marita Boettcher
Keyword(s):  
Wind Speed ◽  
Urban Areas ◽  
Climate Model ◽  
Numerical Models ◽  
Urban Climate ◽  
Cloud Microphysics ◽  
In Situ Measurements ◽  
Small Scale ◽  
Atmospheric Processes

&lt;p&gt;Urbanisation locally modifies the regional climate: an urban climate develops. For example, the average wind speed in cities is reduced, while the gustiness is increased. Buildings induce vertical winds, which influence the falling of rain. All these processes lead to heterogeneous patterns of rain at ground and on building surfaces. The small-scale spatial rain heterogeneities may cause discomfort for people. Moreover, non-uniform wetting of buildings affects their hydrothermal performance and durability of their facades.&lt;/p&gt;&lt;p&gt;Measuring rain heterogeneities between buildings is, however, nearly impossible. Building induced wind gusts negatively influence the representativeness of in-situ measurements, especially in densely urbanised areas. Weather radars are usually too coarse and, more importantly, require an unobstructed view over the domain and thus do not measure ground precipitation in urban areas. Consequently, researchers turn to numerical modelling in order to investigate small-scale precipitation heterogeneities between buildings.&lt;/p&gt;&lt;p&gt;In building science, numerical models are used to investigate rain heterogeneities typically focussing on single buildings and vertical facades. Only few studies were performed for more than a single building or with inclusion of atmospheric processes such as radiation or condensation. In meteorology, increasing computational power now allows the use of small-scale obstacle-resolving models resolving atmospheric processes while covering neighbourhoods.&lt;/p&gt;&lt;p&gt;In order to assess rain heterogeneities between buildings we extended the micro-scale and obstacle-resolving transport- and stream model MITRAS (Salim et al. 2019). The same cloud microphysics parameterisation as in its mesoscale sister model METRAS (Schl&amp;#252;nzen et al., 2018) was applied and boundary conditions for cloud and rain water content at obstacle surfaces were introduced. MITRAS results are checked for plausibility using radar and in-situ measurements (Ferner et al., 2021). To our knowledge MITRAS is the first numerical urban climate model that includes rain and simulates corresponding processes.&lt;/p&gt;&lt;p&gt;Model simulations were initialised for various wind speeds and mesoscale rain rates to assess their influence on the heterogeneity of falling rain in a domain of 1.9 x 1.7 km&amp;#178; around Hamburg City Hall. We investigated how wind speed or mesoscale rain rate influence the precipitation patterns at ground and at roof level. Based on these results we assessed the height dependence of precipitation. First analyses show that higher buildings receive more rain on their roofs than lower buildings; the results will be presented in detail in our talk.&lt;/p&gt;&lt;p&gt;Ferner, K.S., Boettcher, M., Schl&amp;#252;nzen, K.H. (2021): Modelling the heterogeneity of rain in an urban neighbourhood. Publication in preparation&lt;/p&gt;&lt;p&gt;Salim, M.H., Schl&amp;#252;nzen, K.H., Grawe, D., Boettcher, M., Gierisch, A.M.U., Fock B.H. (2018): The microscale obstacle-resolving meteorological model MITRAS v2.0: model theory. Geosci. Model Dev., 11, 3427&amp;#8211;3445, https://doi.org/10.5194/gmd-11-3427-2018.&lt;/p&gt;&lt;p&gt;Schl&amp;#252;nzen, K.H., Boettcher, M., Fock, B.H., Gierisch, A.M.U., Grawe, D., and Salim, M. (2018): Scientific Documentation of the Multiscale Model System M-SYS. Meteorological Institute, Universit&amp;#228;t Hamburg. MEMI Technical Report 4&lt;/p&gt;

scholarly journals Small-Scale Variability in Sea Surface Salinity and Implications for Satellite-Derived Measurements

2013 ◽  
Vol 30 (11) ◽  
pp. 2689-2694 ◽  
Author(s):  
Nadya T. Vinogradova ◽  
Rui M. Ponte
Keyword(s):  
Sampling Error ◽  
In Situ Measurements ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Small Scale ◽  
Surface Salinity ◽  
Ocean Data Assimilation ◽  
Ocean Salinity ◽  
Mean Square Difference

Abstract Calibration and validation efforts of the Aquarius and Soil Moisture and Ocean Salinity (SMOS) satellite missions involve comparisons of satellite and in situ measurements of sea surface salinity (SSS). Such estimates of SSS can differ by the presence of small-scale variability, which can affect the in situ point measurement, but be averaged out in the satellite retrievals because of their large footprint. This study quantifies how much of a difference is expected between in situ and satellite SSS measurements on the basis of their different sampling of spatial variability. Maps of sampling error resulting from small-scale noise, defined here as the root-mean-square difference between “local” and footprint-averaged SSS estimates, are derived using a solution from a global high-resolution ocean data assimilation system. The errors are mostly &lt;0.1 psu (global median is 0.05 psu), but they can be &gt;0.2 psu in several regions, particularly near strong currents and outflows of major rivers. To examine small-scale noise in the context of other errors, its values are compared with the overall expected differences between monthly Aquarius SSS and Argo-based estimates. Results indicate that in several ocean regions, small-scale variability can be an important source of sampling error for the in situ measurements.

In situ measurements of coupled wind-wave dynamics using PIV

2020 ◽  
Author(s):  
Marc Buckley ◽  
Jochen Horstmann
Keyword(s):  
Boundary Layers ◽  
In Situ Measurements ◽  
Large Field ◽  
Small Scale ◽  
Wave Dynamics ◽  
Image Velocimetry ◽  
First Results ◽  
Oceanic Wave ◽  
Wave Boundary

&lt;p&gt;Small-scale turbulent dynamics within the coupled atmospheric and oceanic wave boundary layers control air-sea fluxes of momentum and scalars. However measuring and understanding small-scale dynamics very close to the rapidly moving ocean surface remains technically challenging.&lt;/p&gt;&lt;p&gt;We present novel in situ measurements of small-scale motions in the airflow above, and in the water below the wavy air-water interface. A high resolution, large field of view PIV system (Particle Image Velocimetry) was developed for in situ air-water measurements within the first millimeters to meters above and below the wavy surface. The system was recently deployed on a single pile platform in the Szczecin lagoon (Baltic Sea coast, Germany). We will show first results and we will discuss the influence of waves on the partitioning of momentum flux within the coupled air-water wave boundary layers.&lt;/p&gt;

scholarly journals An indirect-calibration method for non-target quantification of trace gases applied to a time series of fourth-generation synthetic halocarbons at the Taunus Observatory (Germany)

2021 ◽  
Vol 14 (6) ◽  
pp. 4669-4687
Author(s):  
Fides Lefrancois ◽  
Markus Jesswein ◽  
Markus Thoma ◽  
Andreas Engel ◽  
Kieran Stanley ◽  
...  
Keyword(s):  
Stratospheric Ozone ◽  
Trace Gases ◽  
Mass Range ◽  
Calibration Method ◽  
In Situ Measurements ◽  
Atmospheric Composition ◽  
Fourth Generation ◽  
Calibration Gas ◽  
Tof Ms

Abstract. Production and use of many synthetic halogenated trace gases are regulated internationally due to their contribution to stratospheric ozone depletion or climate change. In many applications they have been replaced by shorter-lived compounds, which have become measurable in the atmosphere as emissions increased. Non-target monitoring of trace gases rather than targeted measurements of well-known substances is needed to keep up with such changes in the atmospheric composition. We regularly deploy gas chromatography (GC) coupled to time-of-flight mass spectrometry (TOF-MS) for analysis of flask air samples and in situ measurements at the Taunus Observatory, a site in central Germany. TOF-MS acquires data over a continuous mass range that enables a retrospective analysis of the dataset, which can be considered a type of digital air archive. This archive can be used if new substances come into use and their mass spectrometric fingerprint is identified. However, quantifying new replacement halocarbons can be challenging, as mole fractions are generally low, requiring high measurement precision and low detection limits. In addition, calibration can be demanding, as calibration gases may not contain sufficiently high amounts of newly measured substances or the amounts in the calibration gas may have not been quantified. This paper presents an indirect data evaluation approach for TOF-MS data, where the calibration is linked to another compound which could be quantified in the calibration gas. We also present an approach to evaluate the quality of the indirect calibration method, select periods of stable instrument performance and determine well suited reference compounds. The method is applied to three short-lived synthetic halocarbons: HFO-1234yf, HFO-1234ze(E), and HCFO-1233zd(E). They represent replacements for longer-lived hydrofluorocarbons (HFCs) and exhibit increasing mole fractions in the atmosphere. The indirectly calibrated results are compared to directly calibrated measurements using data from TOF-MS canister sample analysis and TOF-MS in situ measurements, which are available for some periods of our dataset. The application of the indirect calibration method on several test cases can result in uncertainties of around 6 % to 11 %. For hydro(chloro-)fluoroolefines (denoted H(C)FOs), uncertainties up to 23 % are achieved. The indirectly calculated mole fractions of the investigated H(C)FOs at Taunus Observatory range between measured mole fractions at urban Dübendorf and Jungfraujoch stations in Switzerland.

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