Aircraft-Based AirCore Sampling for Estimates of N<sub>2</sub>O and CH<sub>4</sub> Emissions

Airborne measurements offer an effective way to quantify urban emissions of greenhouse gases (GHGs). However, it may be challenging due to the requirement of high measurement precision and sufficiently enhanced signals. We developed a new active AirCore system based on the previous unmanned aerial vehicle (UAV) version, which is capable of sampling atmospheric air for several hours aboard a lightweight aircraft for postflight simultaneous and continuous measurements of N2O, CH4, CO2, and CO. We performed 13 flights over the urban areas of Groningen, Utrecht, and Rotterdam and evaluated the aircraft-based AirCore measurements against in situ continuous CH4 measurements. One flight was selected for each of the three urban areas to quantify the emissions of N2O and CH4. Compared to the Dutch inventory, the estimated N2O emissions (364 ± 143 kg h–1) from the Rotterdam area are ∼3 times larger, whereas those for Groningen (95 ± 90 kg h–1) and Utrecht (32 ± 16 kg h–1) are not significantly different. The estimated CH4 emissions for all three urban areas (Groningen: 2534 ± 1774 kg CH4 hr–1, Utrecht: 1440 ± 628 kg CH4 hr–1, and Rotterdam: 2419 ± 922 kg CH4 hr–1) are not significantly different from the Dutch inventory. The innovative aircraft-based active AirCore sampling system provides a robust means of high-precision and continuous measurements of multiple gas species, which is useful for quantifying GHG emissions from urban areas

Aircraft-Based AirCore Sampling for Estimates of N<sub>2</sub>O and CH<sub>4</sub> Emissions

Airborne measurements offer an effective way to quantify urban emissions of greenhouse gases (GHGs). However, it may be challenging due to the requirement of high measurement precision and sufficiently enhanced signals. We developed a new active AirCore system based on the previous unmanned aerial vehicle (UAV) version, which is capable of sampling atmospheric air for several hours aboard a lightweight aircraft for postflight simultaneous and continuous measurements of N2O, CH4, CO2, and CO. We performed 13 flights over the urban areas of Groningen, Utrecht, and Rotterdam and evaluated the aircraft-based AirCore measurements against in situ continuous CH4 measurements. One flight was selected for each of the three urban areas to quantify the emissions of N2O and CH4. Compared to the Dutch inventory, the estimated N2O emissions (364 ± 143 kg h–1) from the Rotterdam area are ∼3 times larger, whereas those for Groningen (95 ± 90 kg h–1) and Utrecht (32 ± 16 kg h–1) are not significantly different. The estimated CH4 emissions for all three urban areas (Groningen: 2534 ± 1774 kg CH4 hr–1, Utrecht: 1440 ± 628 kg CH4 hr–1, and Rotterdam: 2419 ± 922 kg CH4 hr–1) are not significantly different from the Dutch inventory. The innovative aircraft-based active AirCore sampling system provides a robust means of high-precision and continuous measurements of multiple gas species, which is useful for quantifying GHG emissions from urban areas

Magnitude and seasonal variation of N2O and CH4 emissions over a mixed agriculture-urban region

Inventory estimates of N2O and CH4 emissions disregard temporal and spatial variabilities, which hinders the search for effective local strategies to lower greenhouse gas emissions. We have quantified the emissions of N2O and CH4 in a mixed agriculture-urban region using two independent approaches, i.e., the vertical gradient method (VGM) and the radon-tracer method (RTM), compared the estimated annual fluxes with the EDGARv6.0 emissions, revealed the seasonal variations of the VGM fluxes, and inferred the sources that most likely cause the seasonal variations based on the footprint analysis even though our methods cannot attribute different sources. We show that the annual RTM estimates represented by the mode of lognormal fit for N2O and CH4 are 0.4 g m−2 yr−1 and 12 g m−2 yr−1, and the VGM estimates are 0.6 ± 0.3 g m−2 yr−1 and 13 ± 4 g m−2 yr−1, respectively. Furthermore, the average EDGARv6.0 emissions constrained by the VGM and the RTM footprints are 1.3 g m−2 yr−1 and 0.9 g m−2 yr−1 for N2O, and 21 g m−2 yr−1 and 18 g m−2 yr−1 for CH4. Compared to our estimated fluxes, EDGARv6.0 N2O and CH4 emissions are both overestimated; for N2O, it is mainly caused by an overestimation of the chemical industry's emission. Moreover, in contrast to EDGARv6.0′s nearly constant monthly emissions throughout the year, the VGM estimates of N2O and CH4 show seasonal variations with relatively high values from March to September, which is most likely caused by agricultural activities. Our study demonstrates that large nighttime vertical gradients of atmospheric N2O and CH4 mole fractions at a tall tower can be used to derive surface fluxes by the VGM; taken together with the RTM fluxes, both the annual means and the temporal variations of N2O and CH4 emissions can be constrained on a regional scale

Magnitude and seasonal variation of N2O and CH4 emissions over a mixed agriculture-urban region

Inventory estimates of N2O and CH4 emissions disregard temporal and spatial variabilities, which hinders the search for effective local strategies to lower greenhouse gas emissions. We have quantified the emissions of N2O and CH4 in a mixed agriculture-urban region using two independent approaches, i.e., the vertical gradient method (VGM) and the radon-tracer method (RTM), compared the estimated annual fluxes with the EDGARv6.0 emissions, revealed the seasonal variations of the VGM fluxes, and inferred the sources that most likely cause the seasonal variations based on the footprint analysis even though our methods cannot attribute different sources. We show that the annual RTM estimates represented by the mode of lognormal fit for N2O and CH4 are 0.4 g m−2 yr−1 and 12 g m−2 yr−1, and the VGM estimates are 0.6 ± 0.3 g m−2 yr−1 and 13 ± 4 g m−2 yr−1, respectively. Furthermore, the average EDGARv6.0 emissions constrained by the VGM and the RTM footprints are 1.3 g m−2 yr−1 and 0.9 g m−2 yr−1 for N2O, and 21 g m−2 yr−1 and 18 g m−2 yr−1 for CH4. Compared to our estimated fluxes, EDGARv6.0 N2O and CH4 emissions are both overestimated; for N2O, it is mainly caused by an overestimation of the chemical industry's emission. Moreover, in contrast to EDGARv6.0′s nearly constant monthly emissions throughout the year, the VGM estimates of N2O and CH4 show seasonal variations with relatively high values from March to September, which is most likely caused by agricultural activities. Our study demonstrates that large nighttime vertical gradients of atmospheric N2O and CH4 mole fractions at a tall tower can be used to derive surface fluxes by the VGM; taken together with the RTM fluxes, both the annual means and the temporal variations of N2O and CH4 emissions can be constrained on a regional scale

Evaluation of a field-deployable Nafion (TM)-based air-drying system for collecting whole air samples and its application to stable isotope measurements of CO2

Atmospheric flask samples are either collected at atmospheric pressure by opening a valve of a pre-evacuated flask or pressurized with the help of a pump to a few bar above ambient pressure. Under humid conditions, there is a risk that water vapor in the sample leads to condensation on the walls of the flask, notably at higher than ambient sampling pressures. Liquid water in sample flasks is known to affect the CO2 mixing ratios and also alters the isotopic composition of oxygen (17O and 18O) in CO2 via isotopic equilibration. Hence, for accurate determination of CO2 mole fractions and its stable isotopic composition, it is vital to dry the air samples to a sufficiently low dew point before they are pressurized in flasks to avoid condensation. Moreover, the drying system itself should not influence the mixing ratio and the isotopic composition of CO2 or that of the other constituents under study. For the Airborne Stable Isotopes of Carbon from the Amazon (ASICA) project focusing on accurate measurements of CO2 and its singly substituted stable isotopologues over the Amazon, an air-drying system capable of removing water vapor from air sampled at a dew point lower than -2 °C, flow rates up to 12 L min-1 and without the need for electrical power was needed. Since to date no commercial air-drying device that meets these requirements has been available, we designed and built our own consumable-free, power-free and portable drying system based on multitube Nafion™ gas sample driers (Perma Pure, Lakewood, USA). The required dry purge air is provided by feeding the exhaust flow of the flask sampling system through a dry molecular sieve (type 3A) cartridge. In this study we describe the systematic evaluation of our Nafion™-based air sample dryer with emphasis on its performance concerning the measurements of atmospheric CO2 mole fractions and the three singly substituted isotopologues of CO2 (16O13C16O, 16O12C17O and 16O12C18O), as well as the trace gas species CH4, CO, N2O and SF6. Experimental results simulating extreme tropical conditions (saturated air at 33 °C) indicated that the response of the air dryer is almost instantaneous and that approximately 85 L of air, containing up to 4 % water vapor, can be processed staying below a -2 °C dew point temperature (at 275 kPa). We estimated that at least eight flasks can be sampled (at an overpressure of 275 kPa) with a water vapor content below -2 °C dew point temperature during a typical flight sampling up to 5 km altitude over the Amazon, whereas the remaining samples would stay well below 5 °C dew point temperature (at 275 kPa). The performance of the air dryer on measurements of CO2, CH4, CO, N2O, and SF6 and the CO2 isotopologues 16O13C16O and 16O12C18O was tested in the laboratory simulating real sampling conditions by compressing humidified air from a calibrated cylinder, after being dried by the air dryer, into sample flasks. We found that the mole fraction and the isotopic composition difference between the different test conditions (including the dryer) and the base condition (dry air, without dryer) remained well within or very close to, in the case of N2O, the World Meteorological Organization recommended compatibility goals for independent measurement programs, proving that the test condition induced no significant bias on the sample measurements

Near real-time CO₂ fluxes from CarbonTracker Europe for high resolution atmospheric modeling

We present the CarbonTracker Europe High-Resolution system that estimates carbon dioxide (CO2) exchange over Europe at high-resolution (0.1 x 0.2°) and in near real-time (about 2 months latency). It includes a dynamic fossil fuel emission model, which uses easily available statistics on economic activity, energy-use, and weather to generate fossil fuel emissions with dynamic time profiles at high spatial and temporal resolution (0.1 x 0.2°, hourly). Hourly net biosphere exchange (NEE) calculated by the Simple Biosphere model Version 4 (SiB4) is driven by meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis 5th Generation (ERA5) dataset. This NEE is downscaled to 0.1 x 0.2° using the high-resolution Coordination of Information on the Environment (CORINE) land-cover map, and combined with the Global Fire Assimilation System (GFAS) fire emissions to create terrestrial carbon fluxes. An ocean flux extrapolation and downscaling based on wind speed and temperature for Jena CarboScope ocean CO2 fluxes is included in our product. Jointly, these flux estimates enable modeling of atmospheric CO2 mole fractions over Europe. We assess the ability of the CTE-HR CO2 fluxes (a) to reproduce observed anomalies in biospheric fluxes and atmospheric CO2 mole fractions during the 2018 drought, (b) to capture the reduction of fossil fuel emissions due to COVID-19 lockdowns, (c) to match mole fraction observations at Integrated Carbon Observation System (ICOS) sites across Europe after atmospheric transport with the Transport Model, version 5 (TM5) and the Stochastic Time-Inverted Lagrangian Transport (STILT), driven by ERA5, and (d) to capture the magnitude and variability of measured CO2 fluxes in the city centre of Amsterdam (The Netherlands). We show that CTE-HR fluxes reproduce large-scale flux anomalies reported in previous studies for both biospheric fluxes (drought of 2018) and fossil fuel emissions (COVID-19 pandemic in 2020). After transport with TM5, the CTE-HR fluxes have lower root mean square errors (RMSEs) relative to mole fraction observations than fluxes from a non-informed flux estimate, in which biosphere fluxes are scaled to match the global growth rate of CO2 (poor-person inversion). RSMEs are close to those of the reanalysis with the data assimilation system CarbonTracker Europe (CTE). This is encouraging given that CTE-HR fluxes did not profit from the weekly assimilation of CO2 observations as in CTE. We furthermore compare CO2 observations at the Dutch Lutjewad coastal tower with high-resolution STILT transport to show that the high-resolution fluxes manifest variability due to different sectors in summer and winter. Interestingly, in periods where synoptic scale transport variability dominates CO2 variations, the CTE-HR fluxes perform similar to low-resolution fluxes (5–10x coarsened). The remaining 10 % of simulated CO2 mole fraction differ by > 2ppm between the low-resolution and high-resolution flux representation, and are clearly associated with coherent structures ("plumes") originating from emission hotspots, such as power plants. We therefore note that the added resolution of our product will matter most for very specific locations and times when used for atmospheric CO2 modeling. Finally, in a densely-populated region like the Amsterdam city centre, our fluxes underestimate the magnitude of measured eddy-covariance fluxes, but capture their substantial diurnal variations in summer- and wintertime well. We conclude that our product is a promising tool to model the European carbon budget at a high-resolution in near real-time. The fluxes are freely available from the ICOS Carbon Portal (CC-BY-4.0) to be used for near real-time monitoring and modeling, for example as a-priori flux product in a CO2 data-assimilation system. The data is available at https://doi.org/10.18160/20Z1-AYJ2

JRC – Ispra Atmosphere – Biosphere – Climate Integrated monitoring Station : 2011 report

The Institute for Environment and Sustainability provide long-term observations of the atmosphere within international programs and research projects. These observations are performed from the research infrastructure named ABC-IS: Atmosphere-Biosphere-Climate Integrated monitoring station. Most measurements are performed at the JRC-Ispra site. Observations are also carried out from two other platforms: the forest station in San Rossore, and a ship cruising in the Western Mediterranean sea. This document reports about measurement programs, the equipment which is deployed, and the data quality assessment for each site. Our observations are presented, compared to each other, as well as to historical data obtained over the past 25 years at the Ispra site.JRC.H.2-Air and Climat

Evaluation of a field-deployable Nafion (TM)-based air-drying system for collecting whole air samples and its application to stable isotope measurements of CO2

Atmospheric flask samples are either collected at atmospheric pressure by opening a valve of a pre-evacuated flask or pressurized with the help of a pump to a few bar above ambient pressure. Under humid conditions, there is a risk that water vapor in the sample leads to condensation on the walls of the flask, notably at higher than ambient sampling pressures. Liquid water in sample flasks is known to affect the CO2 mixing ratios and also alters the isotopic composition of oxygen (17O and 18O) in CO2 via isotopic equilibration. Hence, for accurate determination of CO2 mole fractions and its stable isotopic composition, it is vital to dry the air samples to a sufficiently low dew point before they are pressurized in flasks to avoid condensation. Moreover, the drying system itself should not influence the mixing ratio and the isotopic composition of CO2 or that of the other constituents under study. For the Airborne Stable Isotopes of Carbon from the Amazon (ASICA) project focusing on accurate measurements of CO2 and its singly substituted stable isotopologues over the Amazon, an air-drying system capable of removing water vapor from air sampled at a dew point lower than &minus;2&thinsp;∘C, flow rates up to 12&thinsp;L&thinsp;min&minus;1 and without the need for electrical power was needed. Since to date no commercial air-drying device that meets these requirements has been available, we designed and built our own consumable-free, power-free and portable drying system based on multitube Nafion&trade; gas sample driers (Perma Pure, Lakewood, USA). The required dry purge air is provided by feeding the exhaust flow of the flask sampling system through a dry molecular sieve (type&nbsp;3A) cartridge. In this study we describe the systematic evaluation of our Nafion&trade;-based air sample dryer with emphasis on its performance concerning the measurements of atmospheric CO2 mole fractions and the three singly substituted isotopologues of CO2 (16O13C16O, 16O12C17O and 16O12C18O), as well as the trace gas species CH4, CO, N2O and SF6. Experimental results simulating extreme tropical conditions (saturated air at 33&thinsp;∘C) indicated that the response of the air dryer is almost instantaneous and that approximately 85&thinsp;L of air, containing up to 4&thinsp;% water vapor, can be processed staying below a &minus;2&thinsp;∘C dew point temperature (at 275&thinsp;kPa). We estimated that at least eight flasks can be sampled (at an overpressure of 275&thinsp;kPa) with a water vapor content below &minus;2&thinsp;∘C dew point temperature during a typical flight sampling up to 5&thinsp;km altitude over the Amazon, whereas the remaining samples would stay well below 5&thinsp;∘C dew point temperature (at 275&thinsp;kPa). The performance of the air dryer on measurements of CO2, CH4, CO, N2O, and SF6 and the CO2 isotopologues 16O13C16O and 16O12C18O was tested in the laboratory simulating real sampling conditions by compressing humidified air from a calibrated cylinder, after being dried by the air dryer, into sample flasks. We found that the mole fraction and the isotopic composition difference between the different test conditions (including the dryer) and the base condition (dry air, without dryer) remained well within or very close to, in the case of N2O, the World Meteorological Organization recommended compatibility goals for independent measurement programs, proving that the test condition induced no significant bias on the sample measurements. </div