Displays

This paper will describe the characteristics and performance of a system to prepare up to ten 50 mL samples of pure CO₂ with on-demand ¹³C/¹²C ratios, together with an optimized calibration system for measurements by Isotope Ratio Infrared Spectroscopy (IRIS) that has allowed measurement of δ¹³C and δ¹⁸O values with 0.02 ‰ reproducibility (1 σ).

The needs for improved quality infrastructure and appropriate reference gases for CO₂ isotope ratio measurements has been a driver for recent research and development activities within the National Metrology Institutes, and the decision of the Gas Analysis Working Group of the CCQM to plan an international comparison (CCQM-P204) of capabilities of measurements of these quantities. The comparison will be coordinated by the BIPM, which has the mission of preparing the comparison samples, and the IAEA, who will assign their isotopic composition on reference scales. The BIPM has developed a preparation facility based on blending of different pure CO₂ sources of very different isotopic compositions, followed by cryogenic trapping and transfer to ten 50 mL cylinders. The target isotopic ratio ¹³C/¹²C can be adjusted by accurate flow measurements.

A Carousel sampling system with bracketing reference gas calibration and dilution system has been designed at the BIPM to allow rapid and accurate analysis of prepared gas mixtures by IRIS. A key feature of the calibration system is to maintain identical treatment of sample and reference gases allowing two-point calibration of up to 14 samples, and appropriate flushing protocols to remove any biases from memory effects of previously sampled gases. Measurements are performed by the IRIS analyzer at a mole fraction of nominally 700 μmol/mol CO₂ in air, by dilution of pure CO₂ gas controlled by individual low-flow mass flow controllers (0.07 ml/min), and with a feedback loop to control mole fractions to ensure that differences between references and sample gas mole faction stay below 2 μmol/mol. This level of control is necessary to prevent biases in measured isotope ratios, the magnitude of which has also been studied with a sensitivity study that is also reported.

The Carousel and IRIS measurements have been validated using pure CO₂ samples prepared with the gas blending facility, covering a range in delta values of -1 ‰ to -45 ‰ vs VPDB, and in all cases measurement reproducibility over several days of testing of 0.02‰ or better (1 σ) were achieved for both δ¹³C and δ¹⁸O, with negligible memory effects.

Samples produced and characterized with the facility will be distributed to institutes participting in the CCQM-P204 comparison exrecise, with measurements foreseen in the first quarter of 2020.

How to cite: Flores, E., Moussay, P., Mussell Webber, E., Chubchenko, I., Rolle, F., Zhang, T., and Wielgosz, R. I.: Comparison of isotope ratio measurement capabilities for CO2: Sample preparation and characterization by Isotope Ratio Infrared Spectroscopy , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8518, https://doi.org/10.5194/egusphere-egu2020-8518, 2020.

Around the world laboratories that are part of the Global Atmospheric Watch (GAW) community conduct atmospheric trace gas measurements under the auspices of the World Meteorological Organisation (WMO). The GAW-WMO defines the inter-laboratory compatibility goals for these measurements, that is the maximum tolerable bias these measurements may have in order to still be useful for modelling and flux studies. The GAW-WMO network compatibility goals for δ¹³C- and δ¹⁸O-CO_2(atm) measurements are 0.01 ‰ and 0.05 ‰ respectively, and for δ¹³C- and δ²H-CH_4(atm) measurements they are 0.02 ‰ and 1 ‰, respectively. It has to be noted that these goals are very ambitious and at the precision limit of current analytical techniques. Nevertheless, in particular the isotopic measurements of atmospheric methane have suffered from considerable inter-laboratory biases of up to 0.5 ‰ and 13 ‰ for δ¹³C- and δ²H-CH_4(atm) measurements in the past (Umezawa et al., 2018).

These inter-laboratory measurement biases have been, and still are in part due to the different standardisation strategies that are used in different laboratories. In order to tackle this problem the stable isotope laboratory at the Max-Planck-Institute for Biogeochemistry (BGC-IsoLab) developed the Jena Reference Air Scale (JRAS-06) that has been in use since 2006. JRAS-06 is the scale realisation of the VPDB-CO₂ scale, and its use is recommended by the GAW-WMO community to standardise δ¹³C- and δ¹⁸O-CO_2(atm) measurements. The JRAS-06 scale is based on CO₂ in air standards where the CO₂ is evolved from standard calcium carbonates (e.g. NBS 19). Using an example dataset of δ¹³C- and δ¹⁸O-CO_2(atm) measurements we show the improved inter-laboratory compatibility that results from using the JRAS-06 standards and scale at two laboratories, the stable isotope laboratory at the Institute of Arctic and Alpine Research (INSTAAR) and BGC-IsoLab.

The BGC-IsoLab is now collaborating with the National Institute of Water and Atmospheric Research (NIWA) in New Zealand in order to develop standards and a unifying scale for δ¹³C- and δ²H-CH_4(atm) measurements analogous to the JRAS-06 scale realisation. Here we show the first results of this collaborative effort towards a JRAS-M(ethane) scale that aims to improve the inter-laboratory compatibility and closely link δ¹³C- and δ²H-CH_4(atm) measurements to the international VPDB-CO₂ and VSMOW scales, respectively.

How to cite: Moossen, H., Englund Michel, S., Sperlich, P., Rothe, M., and Brand, W. A.: Improving inter-laboratory compatibility of atmospheric carbon dioxide and methane isotope measurements., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3539, https://doi.org/10.5194/egusphere-egu2020-3539, 2020.

Widely available reference materials that are traceable and consistent with international stable isotope scales are necessary in order to create a robust and sustainable global measurement infrastructure for isotope ratio of CO₂ and N₂O.

We report on progress towards the production and certification of atmospheric amount fraction greenhouse gas reference materials with isotope ratios spanning the full atmospheric range. Reference materials are produced with a chosen delta value with uncertainties aiming to achieve the WMO GAW data quality objectives for extended compatibility of delta value of of ∂¹³C-CO₂ and ∂¹⁸O-CO₂ of 0.1‰ (northern hemisphere) and amount fraction of 0.2 µmolmol^-1 for CO₂ and 0.3 nmolmol^-1 for N₂O at atmospheric amount fraction ranges.

To illustrate the work towards these challenging goals we present studies of sampling technique and isotope ratio stability with storage, pressure and cylinder passivation. The precision of blending and dilution of source gases is presented alongside studies of measurement instrument precision and drift. Contributing factors from matrix gases are also discussed. 

How to cite: Hill-Pearce, R., Mussell Webber, E., Hillier, A., Moossen, H., Worton, D., and Brewer, P.: Progress towards atmospheric isotope ratio carbon dioxide and nitrous oxide reference materials that meet the WMO-GAW data quality objectives for compatibility , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18389, https://doi.org/10.5194/egusphere-egu2020-18389, 2020.

Measurements of the four most abundant stable isotopocules of N₂O (¹⁴N¹⁴N¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, and ¹⁴N¹⁴N¹⁸O) can provide a valuable constraint on source attribution of atmospheric N₂O. N₂O isotopocules at natural abundance levels can be analyzed by isotope-ratio mass-spectrometry (IRMS) [1] and more recently optical isotope ratio spectroscopy (OIRS) [2]. OIRS instruments can analyze the N₂O isotopic composition in gaseous mixtures in a continuous-flow mode, providing real-time data with minimal or no sample pretreatment, which is highly attractive to better resolve the temporal complexity of N₂O production and consumption processes. Most importantly, OIRS laser spectroscopy is selective for position-specific ¹⁵N substitution due to the existence of characteristic rotational-vibrational spectra.

By allowing both in-situ application and measurements in high temporal resolution, laser spectroscopy has established a new quality of data for research on N₂O in particular and N cycling in general. However, applications remain challenging and are still scarce as a metrological characterization of OIRS analyzers, reporting factors limiting their performance is still missing. In addition, only since recently two pure N₂O isotopocule reference materials have been made available through the United States Geological Survey (USGS), which however, only offer a small range of δ¹⁵N and δ¹⁸O values (< 1 ‰) and are therefore not suited for a two-point calibration approach [3].

This presentation will highlight the recent progress achieved within the framework of the EMPIR project “Metrology for Stable Isotope Reference Standards (SIRS)”, namely:

• (1) The development of pure and diluted N₂O reference materials (RMs), covering the range of isotope values required by the scientific community. These gaseous standards are available as pure N₂O or N₂O diluted in whole air. N₂O RMs were analyzed by an international group of laboratories for δ¹⁵N, δ¹⁸O (MPI-BGC, Tokyo Institute of Technology, UEA), δ¹⁵N^α, δ¹⁵N^ß (Empa, Tokyo Institute of Technology) and δ¹⁷O (UEA) traceable to the existing isotope ratio scales.
• (2) The metrological characterization of the three most common commercial N₂O isotope OIRS analyzers (with/without precon QCLAS, OA-ICOS and CRDS) for gas matrix effects, spectral interferences of enhanced trace gas concentrations (CO₂, CH₄, CO, H₂O), short-term and long-term repeatability, drift and dependence of isotope deltas on N₂O concentrations [4].

In summary, the authors suggest to include appropriate RMs following the identical treatment (IT) principle during every OIRS measurement to retrieve compatible and accurate results. Remaining differences between sample and reference gas composition have to be corrected, by applying analyzer-specific correction algorithms.

[1] Toyoda, S. and N. Yoshida (1999). "Determination of nitrogen isotopomers of nitrous oxide on a modified isotope ratio mass spectrometer." Anal. Chem. 71(20): 4711-4718.

[2] Brewer, P. J. et al. (2019). "Advances in reference materials and measurement techniques for greenhouse gas atmospheric observations." Metrologia 56(3).

[3] Ostrom, N. E. et al. (2018). "Preliminary assessment of stable nitrogen and oxygen isotopic composition of USGS51 and USGS52 nitrous oxide reference gases and perspectives on calibration needs." Rapid Commun. Mass Spectrom. 32(15): 1207-1214.

[4] Harris, S. J., J. Liisberg et al. (2019). "N₂O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison." Atmos. Meas. Tech. Discuss. (in review).

How to cite: Mohn, J., Rupacher, J., Moossen, H., Toyoda, S., Biasi, C., Kaiser, J., Harris, S., Liisberg, J., Wolf, B., Xia, L., Barthel, M., Yu, L., Kantnerová, K., Wei, J., Pearce, R., Webber, E. M., Kelly, B., Blunier, T., Yoshida, N., and Brewer, P. and the Additional co-authors: N2O isotope research: development of reference materials and metrological characterization of OIRS analyzers within the SIRS project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18624, https://doi.org/10.5194/egusphere-egu2020-18624, 2020.

Nitrogen dioxide (NO₂) and nitrogen monoxide (NO) govern the photochemical processes in the troposphere. Although nitrogen oxides have been measured for decades, their quantification remains challenging. The MetNO2 (Metrology for Nitrogen Dioxide) project of the European Metrology Programme for Innovation and Research (EMPIR) aims to improve the accuracy of NO₂ measurements.

In total 15 instruments were intercompared at the World Calibration Centre for nitrogen oxides (WCC-NOx) in Jülich in autumn 2019 within the project. In addition to chemiluminescence detectors (CLD), the instruments encompassed Quantum Cascade Laser Absorption Spectrometers (QCLAS), Iterative CAvity-enhanced Differential optical absorption spectrometers (ICAD) and Cavity Attenuated Phase Shift (CAPS) spectrometers.

During the campaign, air from a gas phase titration unit, air from the environmental chamber SAPHIR or outside air was provided to the instruments via a common inlet line. The participants calibrated their instruments prior and after the campaign with their own calibration procedures. During the campaign, the common inlet line was used for daily calibration to compare standards, calibration techniques and sensitivity drifts of the instruments. NO₂ for calibration was provided either by gas phase titration from NO, from permeation tubes or from gas mixtures produced within the MetNO2 project.

It was observed that measurements by chemiluminescence or CAPS instruments are prone to interferences from humidity and ozone. However, in most cases data can be corrected. Alkyl nitrates and reactive alkenes were also observed to cause interferences in some instruments, while isobutyl nitrite was found to be photolyzed by photolytic converters.

Finally, measurements in ambient air were compared. The nitrogen oxide observations were accompanied with measurements of hydroxyl radical (OH) reactivity and reactive nitrogen species as nitrous acid (HONO), dinitrogen pentoxide (N₂O₅), and chloryl nitrate (ClNO₂). Detailed results of the intercomparison will be presented.

How to cite: Wegener, R. and the The MetNO2 SAPHIR intercomparison team: Intercomparison of nitrogen monoxide and nitrogen dioxide measurements in the atmosphere simulation chamber SAPHIR during the MetNO2 campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6069, https://doi.org/10.5194/egusphere-egu2020-6069, 2020.

Air pollution causes hundreds of thousands of premature deaths every year in Europe [1]. Traffic related Nitrogen dioxide (NO₂) is a key contributor whose concentration is legislated by the Ambient Air Quality Directive (EU, 2008) [2] and the air quality guidelines (AQGs) set by the World Health Organization (WHO). Atmospheric NO₂ concentration has been widely measured by national, regional and global monitoring networks using different instrumentations. SI-traceability is essential to assure data comparability across networks, underpinning long term trend of ambient NO₂.

Traceable and accurate spectral line data [3,4] of NO₂ is essential for optical sensing of NO₂ using in situ [5] and satellite-based equipment. In particular, it is essential for cost-effective light-weight systems with payload restrictions (e.g. TDLAS system [6], e.g. when installed on drones and balloons for which real time calibration using gas cylinders quickly becomes a burden). Within the scope of the EMPIR (The European Metrology Programme for Innovation and Research) MetNO₂ project [7], spectroscopic measurements of the selected NO₂ CRM (certified reference material) has been carried out using the FTIR infrastructure at PTB to a) derive traceable line data of NO₂; b) quantify the amount of impurities, such as HNO₃, N₂O₄, NO, N₂O, CO, H₂O, etc. Here, we report the line intensity and air-broadening coefficients of the 6.3µm v₃ band of NO₂. FTIR-based impurity analysis including their temporal evolution will also be presented.

Acknowledgement

MK and GL thank for technical support from Kai-Oliver Krauss. This work has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. PTB is member of the European Metrology Network for Climate and Ocean Observation (https://www.euramet.org/european-metrology-networks/climate-and-ocean-observation/).

References

[1] Air quality Europe – 2019 report.  EEA Report No 10/2019. https://www.eea.europa.eu/publications/air-quality-in-europe-2019

[2] Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe. https://www.eea.europa.eu/policy-documents/directive-2008-50-ec-of

[3] V. Werwein, J. Brunzendorf, G. Li, A. Serdyukov, O. Werhahn, V. Ebert.  Applied Optics 56 (2017)

[4] V. Werwein, G. Li, J. Brunzendorf, A. Serdyukov, O.Werhahn, V. Ebert. Journal of Molecular Spectroscopy 348, 68-78(2017).

[5] O. Werhahn O, J.C. Petersen (eds.) 2010 TILSAM technical protocol V1_2010-09-29. Available from:                     http://www.euramet.org/fileadmin/docs/projects/934_METCHEM_Interim_Report.pdf.”

[6] J. A. Nwaboh, Z. Qu, O. Werhahn and V. Ebert, Applied Optics 56, E84-E93 (2017)

[7] EMPIR project 16ENV02, “Metrology for Nitrogen Dioxide (MetNO₂)”, http://em-pir.npl.co.uk/metno2/

How to cite: Li, G., Werwein, V., Lüttschwager, A., Kim, M. E., Nwaboh, J., Werhahn, O., and Ebert, V.: FTIR-based spectral line data of the v3 band of NO2 at 6.3 µm and multi-component impurity analysis of NO2 reference gases within the scope of the EMPIR MetNO2 project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21718, https://doi.org/10.5194/egusphere-egu2020-21718, 2020.

Atmospheric aerosol particles can significantly impact the atmospheric radiative balance by scattering and absorbing incoming solar radiation. Additionally, they are known to strongly affect human health. Given the strong variations in geographical distribution of atmospheric aerosols there is a high need for ubiquitous measurements, while the variable chemical composition generates several technical and metrological challenges. Absorption photometers are commonly used to measure the atmospheric mass concentration of light‑absorbing particles like equivalent black carbon (BC_e), which is the most important radiative forcer among aerosol particles due to its strong infrared to visible spectral absorption. Although BC measurements have been done since decades, a reliable metrological aerosol absorption standard to ensure traceable calibration has not been established so far. Due to the wide field implementation there is strong need for a portable, metrological generator of BC-like aerosol particles for in‑field calibration of aerosol absorption photometers. Spark discharge volatilization is an interesting candidate for a BC particle generator, given its robust operation principle and the reduced media requirements.

The spark discharge aerosol generator (SDAG) produces graphitic, BC-like aerosol particles. Most important is the lack of any organic coatings, known from spray or combustion generators, which usually alter the optical properties of the BC particles. The SDAG consists of a chamber purged with an inert gas (usually nitrogen or argon), which houses two graphite electrodes, which are connected to a pulsed high-voltage source with variable pulse frequency and amplitude. In this study, a PALAS DNP 3000 (PALAS GmbH, Germany) has been used for generating graphitic particles and measure their optical properties, aerosol number size distribution and particle morphology by scanning electron microscopy in transmission mode (TSEM). The SDAG was operated by using inert N₂ only (avoiding dilution air), in order to facilitate the transportability and in-field operation. The N₂ flow rate was fixed to 10 l/min. The spark discharge frequency spanned 60 to 600 Hz. The voltage was varied from 2500 to 5000 V.

The mobility count mean diameter (CMD) of the particles produced could be varied from 28 to 80 nm, using the different set points described above. The single scattering albedo of the aerosol particles was almost constant for all operation modes with an average 0.11 ± 0.03. A repeatability analysis over 9 days was done using a single setting mode (140 Hz, 3500 V), which produced particles of 45 nm CMD with a variability of 6 nm CMD (2σ). The total particle number concentration ranged from 8 to 11 x 10⁶ cm^-3 and varied within 8% (1σ) within the different days. Hence, the SDAG is a promising source of stable, nascent and uncoated, graphitic BC particles and thus has good potential to improve field BC calibration.

This research is part of an international project that aims to establish a BC reference material and calibration procedure (EMPIR 16ENV02 ”Black Carbon”, http://www.empirblackcarbon.com/).

How to cite: Saturno, J., Nowak, A., Jahn, M., Klein, T., Müller, T., and Ebert, V.: Spark discharge aerosol generator for field calibration of absorption photometers: Aerosol properties and stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13471, https://doi.org/10.5194/egusphere-egu2020-13471, 2020.

Optical isotope ratio spectroscopy (OIRS) has recently gained popularity and maturity in isotope research because it simplifies the measurement process and makes isotope ratio measurements in atmospheric greenhouse molecule gases, e.g. CO₂, N₂O, CH₄, more accessible to field research and monitoring networks. OIRS is advantageous in terms of high time resolution, possibility of in-situ measurements and simplified sampling process. However, compared to traditional, high accurate isotope ratio mass spectrometry (IRMS), spectroscopic methods are not yet well established for the highest precision quantification of delta values and agreed recommendations for best practices are still missing. From a metrological point of view, the concept of uncertainty assessment in OIRS field measurements needs to be reported in accordance to the terms of the “Guide to the expression of uncertainty in measurement” (GUM, ISO/IEC Guide 98-3:2008). GUM compliant uncertainty estimation is necessary to assess the metrological comparability of OIRS measurement results. 

In this study we discuss calibration strategies for δ¹³C-CO₂ and δ¹⁸O-CO₂ measurements with commercial mid-IR OIRS instrumentation (Thermo Scientific Delta Ray), an uncertainty budget for OIRS measurements estimated according to the GUM, and compare the calibration strategies recommended by the manufacturer with our new metrological calibration procedure, which considers aspects so far limiting the accuracy as, e.g., matrix gas effects, CO₂ concentration dependence, instrumental drift corrections, and isotope calibration gas uncertainties.

Acknowledgments. This study has received funding from the European Metrology Programme for Innovation and Research (EMPIR) co-financed by the EURAMET Participating States and from the European Union's Horizon 2020 research and innovation programme as of the SIRS project (16ENV06).  PTB is a member of the European Metrology Network for Climate and Ocean Observation.

How to cite: Prokhorov, I., Chubchenko, I., Werhahn, O., and Ebert, V.: Metrological calibration strategies and uncertainty assessments for spectroscopic mid-IR isotope ratio measurements in carbon dioxide, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-221, https://doi.org/10.5194/egusphere-egu2020-221, 2020.

During liquid-vapor phase transition, CO₂ can undergo isotopic fractionation in both C and O.  This phase transition can occur during routine cylinder handling, such as gas expansion or while subjecting the cylinder to cold temperatures without allowing the cylinders to come to thermal equilibrium prior to use. 

This work examines the isotope changes for both C and O in a series of controlled experiments on dual phase (liquid-vapor) and single-phase (vapor only) carbon dioxide contained in pressurized gas cylinders at sub-freezing, ambient and elevated temperatures.  The isotopic values were measured during the temperature equilibration from either cold or elevated temperatures to room temperature.  Isotopic values were observed to vary when the gas was at sub-freezing temperatures but not from elevated temperatures.  Stable isotope practitioners, who rely on pressurized carbon dioxide as a working IRMS laboratory reference gas, will find this work useful.

How to cite: Jacksier, T. and Socki, R.: Carbon and Oxygen Isotope Fractionation of Pressurized CO2 as a Function of Temperature, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1473, https://doi.org/10.5194/egusphere-egu2020-1473, 2020.

      Our process-based understanding of stable isotope signals, as well as technological developments, has progressed significantly, opening new frontiers in marine interdisciplinary research. This has promoted the broad utilisation of carbon and oxygen isotope applications to gain insight into carbon cycling in marine ecosystems and their interaction with the atmosphere.

Our study was performed in the Gulf of Trieste in the N Adriatic where the influence of biological processes, riverine loads and local climate conditions on the atmosphere-water CO₂ exchange and on the carbonate system equilibrium was investigated, in order to elucidate what drives the CO₂ exchange and to estimate the vulnerability of the Gulf of Trieste to acidification processes. On an annual scale, the Gulf of Trieste clearly acts as a sink of CO₂, strongly controlled by the seasonal variability of water temperature, biological processes, wind speed and riverine inputs. The calculated air-sea CO₂ flux was estimated to be -1.47 ± 1.41 mol C m^-2 yr^-1. The sink was generally stronger during the winter months, whereas during early summer and autumn the CO₂ fluxes were lower. It was interesting to note that the atmospheric CO₂ concentrations exhibited large fluctuations on a daily basis, as well as on a seasonal time scale. The average atmospheric CO₂ concentration during our study in 2013 was 438 ± 16 ppm. This is significantly higher than the global average, which, at the time was around 400 ppm. Further The isotopic composition of carbon in atmospheric carbon dioxide (δ¹³C_CO2,air) values panned from -12.7‰ to -9.1‰ with an average value of -10.8 ± 0.9‰. This is considerably different to the “background” value of -8‰ (from NOAA/ESRL) and can most probably be attributed to the presence of fossil fuel emissions. The results are comparable with the data obtained in the Adriatic between Ravenna and Otranto.

The presented study indicate that the quality and comparability of datasets is critical to improve the estimation of processes that influence the carbon dynamics in marine environment. Thus, the implementation of the principle in our laboratory, the monitoring of our measurement quality, validation and status of newly developed gas CO₂ reference materials (SIRS1, SIRS2 and SIRS3) as a part of SIRS project will be also presented.

How to cite: Krajnc, B., Tamše, S., and Ogrinc, N.: The importance of appropriate isotope reference standards for determination of the isotopic composition of C and O in atmospheric CO2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18746, https://doi.org/10.5194/egusphere-egu2020-18746, 2020.

Climate change is one of the most urgent issues facing humanity today. Humans have been rapidly changing the balance of gases in the atmosphere which causes global warming. Burning fossil fuels like coal and oil, farming and forestry, agriculture and cement manufacture cause to release water vapor, carbon dioxide (CO₂), methane (CH₄), ozone and nitrous oxide (N₂O) known as the primary greenhouse gases. According to Intergovernmental Panel on Climate Change (IPCC), carbon dioxide is the most common greenhouse gas absorbing infrared energy emitted from the earth, preventing it from returning to space. It is necessary to separate man-made (anthropogenic) emissions from natural contributions in the atmosphere to obtain accurate emission data [1-4]. Since it could not be achieved with the existing metrological infrastructure, it is required to develop the measurements and references of stable isotopes of CO₂. In this study, static and dynamic reference materials for pure CO₂ at 400 µmol/mol in air matrix were prepared and it was provided to simulate CO₂ gas in the atmosphere.

The static gas mixtures were prepared gravimetrically in accordance with the ISO 6142-1 standard. In order to obtain CO₂ gas at desired isotopic compositions, commercial CO₂ gases were also supplied from abroad. Their isotopic compositions were measured by using GC-IRMS. Before filling, aluminum cylinders were evacuated until the pressure of 10^-7 mbar using turbo-molecular vacuum pump. Isotopic compositions of reference materials were determined in a way that covering the range -42 ‰ to +1 ‰ vs VPDB for d¹³C-CO2 and -35 ‰ to -8 ‰ vs VPDB for d¹⁸O. In order to develop static and dynamic reference materials of CO₂ at 400 µmol/mol in air with the uncertainty targets of d¹³C-CO₂ 0.1 ‰ and d¹⁸O-CO₂ 0.5 ‰, previously prepared pure CO₂ reference gases were used. Dynamic dilution system with the high accuracy was constructed to generate dynamic reference gas mixture of CO₂ at 400 µmol/mol. System contains 3 electronic pressure controllers, 3 thermal mass flow controllers with various capacities and 3 molbloc-L flow elements commanded with 2 Molboxes. The isotopic compositions of dynamic reference gas mixtures of CO₂ at 400 µmol/mol were aimed to be same with the previously prepared pure CO₂ reference gases. The whole dilution system were calibrated at INRIM to achieve lower uncertainties around 0.07-0.09%. At the measurement stage, CRDS and GC-IRMS equipments are operated simultaneously to determine the concentrations and isotopic compositions of the gas mixtures. The amount of substance fractions of the dynamic reference mixtures are calculated according to ISO 6145-7 standard. It will be checked that whether the isotopic compositions of the gravimetrically prepared pure CO₂ reference gases and the dynamic reference gas mixtures of CO₂ at 400 µmol/mol were same or not.

REFERENCES

[1] Calabro P. S., “Greenhouse gases emission from municipal waste management: The role of separate collection”, Waste Management, Volume 29:7, 2178-2187, 2009.

[2] Sources of Greenhouse Gas Emissions, United States Environmental Protection Agency, https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions, 2019.

[3] Schwartz, S.E., “The Greenhouse Effect and Climate Change”, 2017.

[4] Climate Change, The Intergovernmental Panel on Climate Change, https://www.ipcc.ch/report/ar4/wg1, 2019.

How to cite: Boztepe, A., Tarhan, T., Gülsoy Şerif, Z., and Şimşek, A.: DEVELOPING STATIC AND DYNAMIC STABLE ISOTOPE REFERENCE GAS MIXTURES OF CO2 AT 400 µmol/mol, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21827, https://doi.org/10.5194/egusphere-egu2020-21827, 2020.

   Nitrogen dioxide (NO₂) is an atmospheric pollutant whose emissions are mostly linked to anthropogenic activities. It is, with nitric oxide (NO), the most abundant member of the nitrogen oxides family in tropospheric urban air (mixing ratios up to hundreds of ppbv), with a lifetime ranging from hours to days. NO₂ is well known for its role as a boundary layer ozone and organic nitrates precursor and for affecting the oxidation capacity of the atmosphere. It has thus been subject to emissions mitigation policies and ambient air amount fraction monitoring for a few decades. The latter fully relies on the Chemiluminescence Detection technique (CLD), which is an indirect method measuring NO₂ after conversion to NO.
   Recent advances in spectroscopy led to the development of direct and more selective ways to measure NO₂. The currently running European Metrology for Nitrogen Dioxide (MetNO2) project, involving more than 15 European academic and industrial partners, promises to fill the gap in reliable and complete datasets for laboratory and field testing of those measurement techniques.
Here we present the results of a performance investigation of a high precision Quantum Cascade Laser Absorption Spectrometer (QCLAS) for the selective measurement of NO₂ performed in the frame of the MetNO2 project. This instrument is based on a mid-IR QCL emitting at 6 μm and a custom-made, low noise astigmatic Herriott type multipass cell with an effective optical path length of 100 m to measure NO₂ concentration in the low pptv range. We focus on determining precision, long-term stability and potential biases related to sampling conditions such as ambient pressure, temperature and humidity. The QCLAS device is then compared to other direct spectroscopic (CAPS, CRDS, IBBCEAS) and indirect (CLD) techniques. We also report on the results of a three weeks side-by-side field comparison at an urban air monitoring station of the Swiss National Air Pollution Monitoring Network (NABEL), involving the newly developed QCLAS, and commercial CAPS and CLD instruments.
   We show that the QCLAS is well suited for monitoring of NO₂ concentration in ambient air and its performances in term of precision and stability surpass those of the CLD device and compete well with other direct measurement techniques.

How to cite: Sobanski, N., Schwarzenbach, B., Tuzson, B., Emmenegger, L., Worton, D. R., Farren, N., Mace, T., and Sutour, C.: Development and characterization of a high precision QCLAS for selective NO2 measurement, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14771, https://doi.org/10.5194/egusphere-egu2020-14771, 2020.

As a toxic and reactive gas, nitrogen dioxide (NO₂) influences air quality and health, the self-cleaning power of the atmosphere and photochemical smog formation. Reliable scientific data with high quality and comparability are required for national and international decision-makers. The quality of the NO₂ measurements is crucially dependent on the quality of the calibration standards. In order to achieve the quality goals required, the MetNO2 project within the EMPIR (European Metrology Program for Innovation and Research) program aims to provide accurate and stable NO₂ calibration standards for operational use at air quality stations.

To characterise the impurities of the newly developed standards a Thermal Dissociation - Cavity Attenuated Phase Shift (TD - CAPS) system has been set up, based on the design from Sadanaga et al. (2016). The device includes four heated channels for the differentiation of NO₂, peroxy and alkyl nitrates and HNO₃. In parallel, a gold converter coupled with a chemiluminescence detector was deployed for detection of the total sum of NO_y. First results of the performance of the TD-CAPS used for impurity analysis of NO₂ standards will be presented.

Reference: Sadanaga et al. Review of Scientific Instruments 87.7 (2016), 074102

How to cite: Kuß, A., Kubistin, D., Holla, R., Plaß-Dülmer, C., Tensing, E., Utschneider, F., Prosteder, M., Worton, D. R., Persijn, S., Iturrate-Garcia, M., and Wegener, R.: A thermal dissociation CAPS for detection of NOy species within the MetNO2 project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17866, https://doi.org/10.5194/egusphere-egu2020-17866, 2020.

Nitrogen dioxide (NO₂) is an atmospheric pollutant that needs to be accurately measured for air quality control. The standard reference method (SRM, as laid down in EN 14211:2012 [1]) for NO₂ emissions is based on chemiluminescence, where NO₂ is only indirectly measured. Due to the fact that NO₂ is the only air pollutant that is indirectly measured and because of some shortcomings in SRM-based measurements, there are attempts to develop methods also for direct NO₂ quantifications that are accurate and reliable [2, 3]. Laser spectroscopic techniques such as direct tunable diode laser absorption spectroscopy (dTDLAS [4]), which has been demonstrated for direct and absolute measurements of a variety of atmospheric molecules (H₂O, NH₃, CO₂ and CO) [4-7], provide excellent options for direct atmospheric NO₂ measurements. Based on the experience with other species, a test method for direct NO₂ measurements based on dTDLAS was found to be a promising alternative as compared to the SRM.

We present a measurement method based on dTDLAS for direct and absolute NO₂ concentration measurements compatible to [8] and complying with metrological principles of SI-traceability. The approach was realized by two independent, newly developed mid infrared (ICL, QCL) laser spectrometers (one aiming at compact and field-deployable system integration). Results of directly measured NO₂ concentrations are presented, addressing traceability to the SI, to demonstrate the capability of the measurement method. Guide to the expression of uncertainty in measurement (GUM) compliant uncertainty budgets are reported to show the current data quality. A first principles laser spectroscopic system which does not need calibration by gaseous reference material and which is validated for concentration results that are directly traceable to the SI shall be referred to as an “optical gas standard”, (OGS). We present validations in the concentration range 100 µmol/mol to 1000 µmol/mol. A discussion on current limitations and potentials for an upscaling of these new NO₂ systems to be operated as OGSs towards ambient air concentrations will be part of this presentation, too.

This work has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. PTB is member of the European Metrology Network for Climate and Ocean Observation (https://www.euramet.org/european-metrology-networks/climate-and-ocean-observation/).

References

[1] European Standard: “Ambient air - Standard method for the measurement of the concentration of nitrogen dioxide and nitrogen monoxide by chemiluminescence”, EN 14211:2012

[2] EMPIR project 16ENV02, “Metrology for Nitrogen Dioxide (MetNO2)”, http://em-pir.npl.co.uk/metno2/

[3] P. Morten Hundt, Michael Müller, Markus Mangold, Béla Tuzson, Philipp Scheidegger, Herbert Looser, Christoph Hüglin, Lukas Emmenegger, Atmos. Meas. Tech., 11, 2669–2681 (2018)

[4] J. A. Nwaboh, Z. Qu, O. Werhahn, V. Ebert, Appl. Opt. 56, E84-E93 (2017)

[5] B. Buchholz, N. Böse, V. Ebert, Appl. Phys. B 116, 883-899, (2014)

[6] J.A. Nwaboh, J. Hald, J.K. Lyngsø, J.C. Petersen, O. Werhahn, Appl. Phys. B 110:187–194 (2013)

[7] A. Pogány, O. Werhahn, V. Ebert, Imaging and Applied Optics 2016, DOI: 10.1364/3D.2016.JT3A.15

[8] Werhahn O, Petersen J C (eds.) 2010 TILSAM technical protocol V1_2010-09-29 (http://www.euramet.org/fileadmin/docs/projects/934_METCHEM_Interim_Report.pdf)

How to cite: Nwaboh, J. A., Qu, Z., Li, G., Kim, M. E., Petersen, J. C., Balslev-Harder, D., Werhahn, O., and Ebert, V.: Diode laser spectrometer for NO2 quantification: Absolute laser spectroscopic and direct NO2 concentration measurements for atmospheric monitoring within the EMPIR project MetNO2 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19259, https://doi.org/10.5194/egusphere-egu2020-19259, 2020.

Three instruments using different measurement techniques were used to measure formaldehyde (HCHO) concentrations during experiments in the atmopshere simulation chamber SAPHIR at the Forschungszentrum Juelich. An AL4021 instrument by Aero Laser GmbH uses the wet-chemical Hantzsch reaction for efficient gas stripping, chemical conversion and fluorescence measurement. An internal permeation gas source provides daily calibrations characterized by sulfuric acid titration. A G2307 analyzer by PICARRO INC. uses Cavity Ring-Down Spectroscopy (CRDS) technique to determine concentrations of HCHO, water and methane. A high-resolution laser differential optical absorption spectroscopy (DOAS) instrument provided HCHO measurements along the central chamber axis using an optical multiple reflection cell. The measurements were conducted from June to December 2019 in experiments when ambient air was flowed through the chamber and also in photochemical experiments in synthetic air with mixtures of different reactants, water vapour, nitrogen oxides, and ozone concentrations. Results demonstrate the importance for a linear base line interpolation between zero measurements for the Hantzsch instrument. In addition, a strong water dependence of the baseline of CRDS measurements was found. After correction for the baselines, the correlation analysis of measurements demonstrate good agreement (R > 0.98) between the instruments.

How to cite: Glowania, M., Fuchs, H., Rohrer, F., Dorn, H.-P., Holland, F., and Tillmann, R.: Comparison of Formaldehyde Measurements by HANTZSCH, CRDS and DOAS instruments in the SAPHIR Chamber, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8833, https://doi.org/10.5194/egusphere-egu2020-8833, 2020.

For reactive gaseous compounds, limited availability of bottled standard gases often limits their measurement accuracy and comparability. Typically, an available reference gas concentration range for the specific compounds may be limited to even orders of magnitude higher than the levels normally measured at atmospheric measurements and most often only dry reference gases in inert matrices, typically nitrogen, are available. This means that when applying test gases from cylinders humidity in measurement system may cause significantly longer measurement response than in normal operation.

A real-time reference gas generation is an effective method to circumvent these obstacles. Controlled evaporation of the reference solution enables flexible and reliable generation of test gases in wide concentration and flow ranges as well as in different gas matrices. The method is useable in field conditions and it may provide cost savings since necessary consumables include solely pure carrier gas and solution of the studied chemical with know concentration.

We validate this method for different reactive gaseous compounds and key impurities. For mercury chloride, the most typical form of oxidised mercury in process emissions and atmosphere, reference gas with concentration ranging from sub-ng/m³ to tens of µg/m³ is generated. In case of typical base and acid trace impurities, ammonia, hydrogen chloride and hydrogen fluoride, the reference gases are generated in (bio-) methane and air matrices. In all cases studied, the stabilization time of generating gas flow is no longer, than some minutes. Accuracy and traceability of the generated gas concentration are estimated based on full uncertainty calculation as well as comparison with traceable reference gas standards.

How to cite: Rajamäki, T. and Saxholm, S.: Traceability of real-time reference gas generation for reactive gaseous compounds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7161, https://doi.org/10.5194/egusphere-egu2020-7161, 2020.

Fast measurements of the chemical composition of organic aerosol (OA) at the molecular level are essential to furthering the understanding of the sources and evolution of ambient particulate matter. To that end, we carried out airborne in-situ extractive electrospray time-of-flight mass spectrometry (EESI) measurements of aerosol in a large set of wildland and agricultural fire smoke plumes during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign in summer 2019. We present the methodology that allowed for stable, quantitative measurements of targeted analytes up to altitudes of 7 km. Optimization of electrospray solvent, fine control of electrospray capillary position, pre- and post-flight calibrations, and tightly regulated inlet pressure all contributed to extending airborne EESI measurements to these altitudes.

The EESI was operated with both positive and negative ion polarity during the study, and we report 1-Hz aerosol concentrations of levoglucosan for EESI(+) and nitrocatechol for EESI(-). Campaign-averaged 1-second detection limits for each compound were 720 and 17 ng m-3 during low-altitude sampling. Intercomparison of EESI with an Aerodyne high-resolution Aerosol Mass Spectrometer (AMS) flown during FIREX-AQ shows the fast response time of EESI in concentrated aerosol plumes. Total EESI signal was well correlated with AMS OA for both EESI(+) and EESI(-) measurements, and we present bulk EESI OA sensitivities. We also compare EESI measurements of levoglucosan to a CHemical Analysis of aeRosol ONline Proton-Transfer Reaction Mass Spectrometer (CHARON PTR-MS) flown during FIREX-AQ, demonstrating quantitative agreement between the two instruments. We also compare compounds detected in-situ by EESI with offline electrospray ionization (ESI) of filter samples collected during FIREX-AQ, showing overlap in the detected spectra of the two techniques.

Positive matrix factorization (PMF) of EESI data shows that the chemical composition of biomass burning OA evolves as it is transported downwind, with production of some species and loss of others. This evolution occurs while dilution-corrected OA concentrations remain roughly constant, suggesting that there is a balance between processes that increase and reduce OA concentrations. 

How to cite: Pagonis, D., Campuzano-Jost, P., Guo, H., Day, D., Brown, W., Schueneman, M., Nault, B., Piel, F., Mikoviny, T., Tomsche, L., Wisthaler, A., and Jimenez, J.: Fast Airborne Extractive Electrospray Mass Spectrometry (EESI) Measurements of the Chemical Composition of Biomass Burning Organic Aerosol, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10511, https://doi.org/10.5194/egusphere-egu2020-10511, 2020.

The Aerodyne Aerosol Mass Spectrometer (AMS) is a widely used instrument to quantify the composition of non-refractory submicron aerosol, in particular, organic aerosol (OA). Past comparisons, particularly of aircraft data in continental areas, have shown good overall agreement with other chemical and optical sensors. Recently, theoretically-based concerns have been raised regarding the overall AMS calibration uncertainties (particularly for OA), although there is no evidence that those apply to aircraft datasets.

The ATom mission sampled the remote marine troposphere from 87S to 82N and from 0 to 12.5 km over the course of four aircraft deployments over the space of 2 years, carrying an advanced aerosol payload that included particle sizing instruments operated by NOAA ESRL, as well as several chemical sensors: UNH Mist Chamber and Filters for inorganic aerosol, NOAA SP2 for black carbon measurements, NOAA PALMS instrument for single particle composition and the CU aircraft high-resolution AMS for non-refractory submicron mass. This provides a unique opportunity to explore the agreement of the different instruments over a very large range of conditions and calibration regimes, and improve our understanding of the various instrumental uncertainties in field data.

Special attention was paid to characterize the AMS size-dependent transmission with in-field calibrations; this provided crucial context when comparing with instruments with very different size cuts. Excellent agreement was found between the AMS calculated volume (including black carbon from the SP2) and the PM1 volume derived from the NOAA particle sizing measurements over three orders of magnitude (slope 0.94). The comparisons for sulfate, OA, and seasalt (the three main components of the remote PM1 aerosol) measured by AMS with the PALMS instrument showed similar consistency once differences in particle detection at different sizes were accounted for. Similarly, comparisons with sulfate from filters showed good consistency once episodes with large supermicron mass were filtered out. Comparisons of the AMS with the mist chamber sulfate were affected by the variable time response of the latter instrument but were overall consistent. Overall, no evidence for AMS calibration artifacts or unknown sources of error was found for these datasets. A comprehensive evaluation of the different sources of uncertainty and their impact on the comparisons was performed, and factors to be considered for performing such intercomparisons and improving the reliability of submicron mass quantification in the future are discussed.

How to cite: Guo, H., Campuzano-Jost, P., Nault, B., Day, D., Williamson, C., Kupc, A., Brock, C., Schill, G., Froyd, K., Murphy, D., Scheuer, E., Dibb, J., Katich, J., and Jimenez, J.: Evaluating the Consistency of All Submicron Aerosol Mass Measurements (Total and Speciated) for the NASA Atmospheric Tomography Aircraft Mission (ATom), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11863, https://doi.org/10.5194/egusphere-egu2020-11863, 2020.

Air pollution and extreme weather patterns have become serious issues over the world, especially in highly urbanized areas.  In order to detailed study the atmospheric environmental change, the capability to perform high spatiotemporal resolution atmospheric environmental data collection is highly desired.  In this research, we develop a cost-effective air quality monitoring system based on as open-source electronics platform (Arduino Uno Rev3) with multiple environmental sensing modules including particulate matter (PM) concentration, temperature, humidity, and sound sensors.  An integrated monitoring system with one weather station (precipitation and wind sensors) and two sets of environmental sensors set up in different heights from the ground costs less than USD$300.  The entire system is powered by a battery for portability, and all the data can be stored in a secure digital (SD) memory card for long-term monitoring. The cost-effectiveness makes it feasible for large-scale field tests with three-dimensional (3D) spatial resolution.  In the experiments, the system is tested in urban areas, and the data collection performance has been confirmed.  The results show that the data with single minute resolution can be successfully achieved in real-world scenarios with high air temperature (> 38^oC) and rain conditions for more than 65 hours with a single-time battery setup.  In addition, the data collected from different heights have shown distinct atmospheric environmental patterns suggesting that it is critical to perform 3D high spatiotemporal measurement and modeling for city-scale studies.

How to cite: Tung, Y.-C., Chang, D.-M., and Kuo, C.-Y.: Cost-Effective Air Quality Monitoring System Based on an Open-Source Electronics Platform for Three-Dimensional Atmospheric Environmental Data Collection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8307, https://doi.org/10.5194/egusphere-egu2020-8307, 2020.