Air Quality Science: Lab & Fields
Subramaniam, L., Engelsberger, F., Wolf, B., Brüggemann, N.,Philippot, L., Dannenmann, M., Butterbach‑Bahl, K.
Biol. Fertil. Soils; 2020
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Nitric oxide (NO) is a key substance in atmospheric chemistry, influencing the formation and destruction of tropospheric ozone and the atmosphere's oxidizing capacity. It also affects the physiological functions of organisms. NO is produced, consumed, and emitted by soils, the effects of soil NO concentrations on microbial C and N cycling and associated trace gas fluxes remain largely unclear. This study describes a new automated 12-chamber soil mesocosm system that dynamically changes incoming airflow composition. It was used to investigate how varying NO concentrations affect soil microbial C and N cycling and associated trace gas fluxes under different moisture conditions (30% and 50% WFPS). Based on detection limits for NO, NO2, N2O, and CH4 fluxes of < 0.5 µg N or C m−2 h−1 and for CO2 fluxes of < 1.2 mg C m−2 h−1, we found that soil CO2, CH4, NO, NO2, and N2O were significantly affected by different soil moisture levels. After 17 days cumulative fluxes at 50% WFPS increased by 40, 400, and 500% for CO2, N2O, and CH4, respectively, when compared to 30% WFPS. However, cumulative fluxes for NO, and NO2, decreased by 70, and 50%, respectively, at 50% WFPS when compared to 30% WFPS. Different NO concentrations tended to decrease soil C and N fluxes by about 10–20%. However, with the observed variability among individual soil mesocosms and minor fluxes change. In conclusion, the developed system effectively investigates how and to what extent soil NO concentrations affect soil processes and potential plant–microbe interactions in the rhizosphere.
Air Quality Science: Lab & Fields
Aduse-Poku, M., Rohrer F., Winter B., Edelmann H. G.
SSRN; 2023
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How much do specific climbing plants contribute to the cleansing or absorption of harmful greenhouse and pollutant gases; often regarded as the main environmental threat in cities due to their adverse effects on human health? One of the main hurdles in the quantification of such ecosystem services is associated with the difficulty to obtain and design systems that provide detailed information on the interaction between various gases and the plant in question. To tackle these questions, two highly precise and accurate instruments, namely a mid-infrared laser absorption spectrometer (TDL) and a cavity-ring-down spectrometer (CRDS) were used to monitor the fate of gases when exposed to façade climbing plants like ivy. In a laboratory setting, a relaxation type of experiment was used consisting of a reaction chamber equipped with plant species and continuously flushed by synthetic air. This setup was used to determine the timescales of decay after short injections of the above-mentioned gases. After these injections, all gases followed simple exponential decay curves. N2O, a non-reactive (inert) tropospheric gas, was used as a reference to which all other gases were compared and thereby quantified. This paper focuses on the detailed description of methods and processes to analyse the gas-absorptive behaviour of plants when exposed to gaseous pollutants. For demonstration purposes, quantified absorption features of nitrogen oxide (NO2) are presented for ivy of the variety Hedera helix “Plattensee”. Results of this method of quantification showed that - as compared to N2O (control), - NO2 had a reduced residence time (time scale) of 100 s, while N2O resulted in a 600 s residence time (indicating no interference with the plant). This is equivalent to a 0.3 cm/s deposition velocity/ absorption rate of NO2 under light conditions.
Keywords: Hedera helix, Air phytoremediation, Climbing plants, time scale decay, Residence time, Reactivity, Deposition velocity, Nitrogen dioxide (NO2)
Air Quality Science: Lab & Fields
Eckl, M., Roiger, A., Gottschaldt, K., Waldmann, P., Knez, L., Förster, E., Mallaun, C., Röckmann, T., Hutjes, R., Chen, H., Gerbig, C., Galkowski, M., Kiemle, C.
AGU, Annual Meeting, 2023, San Francisco, CA, USA, 11-15 December ; 2023
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Agriculture is the most important anthropogenic emission sector of the long-living greenhouse gases nitrous oxide (N2O) and methane (CH4) and thus significantly contributes to global warming. The Netherlands exhibits one of the most intensive agriculture worldwide and hence constitutes a European and even global hotspot of agricultural N2O and CH4 emissions. However, the challenging nature of these type of emissions (diffuse area source, large temporal variability, spatial heterogeneity) results in sparse observations and poor model estimates. Hence, agricultural emissions are highly uncertain, especially on a regional scale, hindering the development of effective mitigation strategies. For a better understanding of this important source sector new observational methods and better process understanding is needed.
Here we present our first results of the in-situ aircraft campaign Greenhouse Gas Monitoring (GHGMon) which took place in the Netherlands in June 2023. We conducted 14 science flights using the DLR Cessna in order to characterize agricultural N2O and CH4 emissions in selected areas of this important source region. The DLR Cessna was equipped with a newly developed eddy-covariance system capable of measuring fluxes of N2O and CH4 directly. This will provide additional insights about the underlying emission processes. During the 45 flight hours we were able to study different agricultural subsectors repeatedly and under various meteorological conditions (i.e. before and after rainy periods). We observed large gradients of N2O and CH4 both within the planetary boundary layer (PBL) as well as between the free troposphere and the PBL. First analysis of the turbulence spectra shows a strong correlation between the vertical wind and trace gas concentrations, indicating the measured vertical flux of N2O and CH4. This extensive dataset will lead to a better understanding of the summertime agricultural emissions in the Netherlands.
Air Quality Science: Lab & Fields
Hilland, R., Hashemi, J., Rubli, P., Stagakis, S., Emmenegger, L., Hammer, S., Vogt, R., Christen, A.
AGU, Annual Meeting, 2023, San Francisco, CA, USA, 11-15 December; 2023
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In-situ measurements of urban greenhouse gas (GHG) emissions play a critical role in quantifying cities’ contributions to regional and global emissions and help to both create and validate GHG emission inventories and models. Cities are complex environments containing a multitude of anthropogenic emission sources such as traffic, residential, industrial, etc. Correct sectoral attribution of urban GHG emissions is therefore necessary to monitor emission reduction efforts, to improve validation of emission inventories, and to separate anthropogenic from biogenic emissions.
The eddy-covariance (EC) method generally provides a net carbon dioxide (CO2) flux that integrates all emission sources and sinks and their respective source areas, and includes both anthropogenic and biogenic CO2 fluxes. As part of the EU-funded Integrated Carbon Observation System (ICOS) PAUL (Pilot Applications in Urban Landscapes) project, a tall-tower EC system was one of many systems installed in the centre of Zurich, Switzerland, to explore the potential of concurrently measured fluxes of co-emitted species to support the attribution of CO2 fluxes to fossil fuel sources over their characteristic diurnal, weekly, and seasonal cycles at the city scale.
On a 16.5 m communications mast atop a residential building (112 m above ground level), an open-path EC system (IRGASON, Campbell Scientific) was installed to provide EC fluxes of CO2. A co-located closed-path fast-response multi-species gas analyser (MGA7, MIRO Analytical) provided 10 Hz measurements of CO2, CO, CH4, NO, NO2, and N2O, from which EC fluxes were calculated.
Both systems operated for 8 months from August 2022 until March 2023. Both fluxes and flux ratios of co-emitted species relative to CO2 are investigated and show strong variability with time (diurnal, weekly, seasonal) and source area within the city. Flux ratios are generally in line with the ratios reported in emission inventories. We discuss the potential and the challenges of using multi-species EC measurements to separate urban GHG emission sources.
Air Quality
van Dinther, D., de Bie, S., Velzeboer, I., van den Bulk, P., Frumau, A., and Hensen, A.
EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15779; 2021
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Mobile measurements of greenhouse gasses are used more often for emission evaluation studies (https://h2020-memo2.eu). Over the last few years, TNO have carried out multiple studies using a van to measure greenhouse gasses mobile (e.g. Hensen et.al., 2018 and Hensen & Scharff, 2001). Evaluation of the campaign data sets, where nitrous oxide (N2O) is released as a tracer release and meteorological conditions (windspeed and -direction) are measured, has provided a great quantity of information both on the different sources that are investigated as well as on the evaluation method itself. This study examines a subset of the “random” survey datasets that were obtained while driving in the Netherlands. In general, these are single pass plume measurements that can be used to generate a single shot emission estimate as long as the exact location of the source and local meteorological data are known. In order to automatically indicate different sources, it is assumed that different source types emit different mixtures of trace gasses into the atmosphere, which leave behind a typical ‘’fingerprint’’. A combustion source, for instance, might leak methane (CH4) as well as ethane (C2H6) and produce carbon monoxide (CO) and nitric oxide/nitrogen dioxide (NO/NO2). Farms, on the other hand, produce CH4, ammonia (NH3) and potentially N2O, but in principal no C2H6, CO, NO and NO2. For the mobile measurements of greenhouse gasses the Aerodyne TDLAS instrument was used. This instrument measures CH4, C2H6, N2O, CO2, and CO simultaneously and data is stored at a 1 second time resolution. Since December 2020, the MIRO instrument, which measures CH4, N2O, CO, NH3, Sulphur dioxide (SO2), NO and NO2 on a 1 second time resolution, was added in the van as well. The expected co-emitted species are then used in an algorithm to automatically categorize the mixture of gas in the observed gas plumes into five different source types (farms, traffic, burning, fossil and wastewater treatment plants) and can be viewed per category in Google Earth. Emission levels are subsequently calculated using the TNO Gaussian model that is used in many of our emission studies (e.g. Hensen et.al., 2019) and calibrated versus N2O tracer release tests, which can then be compared to emission registration (ER) numbers. In this study, a subset of available datasets will be shown covering a large part of the Netherlands. Different sources were assigned a source category and, if possible, these sources were assigned an emission level. Some of these locations, for instance along major highways, have multiple “hits” in a year. For these sources, an average and standard deviation in the emission level numbers are provided and compared to ER numbers.
Air Quality
Wegener, R. and the The MetNO2 SAPHIR intercomparison team
EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6069; 2020
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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.
Air Quality Industry Science: Lab & Fields
Tillmann, R., Gkatzelis, G. I., Rohrer, F., Winter, B., Wesolek, C., Schuldt, T., Lange, A. C., Franke, P., Friese, E., Decker, M., Wegener, R., Hundt, M., Aseev, O., and Kiendler-Scharr, A.
Atmos. Meas. Tech., 15, 3827–3842; 2022
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A Zeppelin airship was used as a platform for in situ measurements of greenhouse gases and short-lived air pollutants within the planetary boundary layer
(PBL) in Germany. A novel quantum cascade laser-based multi-compound gas analyzer (MIRO Analytical AG) was deployed to simultaneously measure in situ
concentrations of greenhouse gases (CO2, N2O, H2O, and CH4) and air pollutants (CO, NO, NO2, O3, SO2, and NH3) with high precision at a measurement rate of
1 Hz. These measurements were complemented by electrochemical sensors for NO, NO2, O
x (NO2 + O3), and CO, an optical particle counter, temperature,
humidity, altitude, and position monitoring. Instruments were operated remotely without the need for on-site interactions. Three 2-week campaigns were
conducted in 2020 comprising commercial passenger as well as targeted flights over multiple German cities including Cologne, Mönchengladbach, Düsseldorf,
Aachen, Frankfurt, but also over industrial areas and highways.
Vertical profiles of trace gases were obtained during the airship landing and take-off. Diurnal variability of the Zeppelin vertical profiles was compared to
measurements from ground-based monitoring stations with a focus on nitrogen oxides and ozone. We find that their variability can be explained by the
increasing nocturnal boundary layer height from early morning towards midday, an increase in emissions during rush hour traffic, and the rapid photochemical
activity midday. Higher altitude (250–450 m) NO
x to CO ratios are further compared to the 2015 EDGAR emission inventory to find that pollutant concentrations
are influenced by transportation and residential emissions as well as manufacturing industries and construction activity. Finally, we report NO
x and CO
concentrations from one plume transect originating from a coal power plant and compare it to the EURopean Air pollution Dispersion-Inverse Modell (EURAD-
IM) model to find agreement within 15 %. However, due to the increased contribution of solar and wind energy and the impact of lockdown measures the
power plant was operating at max. 50 % capacity; therefore, possible overestimation of emissions by the model cannot be excluded.
Air Quality Science: Lab & Fields
Schuldt, T., Gkatzelis, G. I., Wesolek, C., Rohrer, F., Winter, B., Kuhlbusch, T. A. J., Kiendler-Scharr, A., and Tillmann, R.
Atmos. Meas. Tech.; 2023
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In this work, we used a Zeppelin NT equipped with six sensor setups, each composed of four different low-cost electrochemical sensors (ECSs) to measure nitrogen
oxides (NO and NO2), carbon monoxide, and O
x (NO2+O3) in Germany. Additionally, a MIRO MGA laser absorption spectrometer was installed as a reference device for
in-flight evaluation of the ECSs. We report not only the influence of temperature on the NO and NO2 sensor outputs but also find a shorter timescale (1 s) dependence
of the sensors on the relative humidity gradient. To account for these dependencies, we developed a correction method that is independent of the reference
instrument. After applying this correction to all individual sensors, we compare the sensor setups with each other and to the reference device. For the intercomparison
of all six setups, we find good agreements with
R2≥0.8 but different precisions for each sensor in the range from 1.45 to 6.32 ppb (parts per billion). The comparison to
the reference device results in an
R2 of 0.88 and a slope of 0.92 for NO
x (NO+NO2). Furthermore, the average noise (1σ) of the NO and NO2 sensors reduces significantly
from 6.25 and 7.1 to 1.95 and 3.32 ppb, respectively. Finally, we highlight the potential use of ECSs in airborne applications by identifying different pollution sources
related to industrial and traffic emissions during multiple commercial and targeted Zeppelin flights in spring 2020. These results are a first milestone towards the
quality-assured use of low-cost sensors in airborne settings without a reference device, e.g., on unmanned aerial vehicles (UAVs).