Significant fluxes of methane over tropical wetlands and their associated δ13C isotopic source signatures

2020 ◽  
Author(s):  
James L. France ◽  
Anna Jones ◽  
Tom Lachlan-Cope ◽  
Alex Weiss ◽  
Marcos Andrade ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Mixed Boundary ◽  
Ground Level ◽  
Isotopic Analysis ◽  
Isotopic Signature ◽  
Direct Access ◽  
Atmospheric Methane ◽  
Tropical Wetlands ◽  
Mixing Ratios ◽  
Methane Fluxes

<p>Tropical wetlands have been proposed as a potential driver for the recent rise in global atmospheric methane. However, direct access and quantification of emissions is difficult. In March 2019, a pilot study was given permission to overfly the Bolivian Llanos de Moxos wetlands to measure atmospheric mixing ratios of methane and collect spot samples for isotopic analysis. Combined with this was a short ground campaign to collect isotopic samples directly above the wetland edge to compare with the integrated atmospheric signature.</p><p>Atmospheric mixing ratios of methane reached a maximum of 2400 ppb (500 ppb above baseline concentrations) in the well mixed boundary layer flying at 400m above the wetland. Upwind and downwind transects were a maximum of 300 km, and methane mixing ratios increased roughly linearly with distance downwind. The isotopic data from the airborne surveys and ground surveys give a bulk isotopic signature for δ<sup>13</sup>C<sub>CH4</sub> of ~-59 ‰ ± 4, which is less negative than Amazon floodplain work focusing on emission of methane through trees, but match well with bulk isotopic values from the Amazon Basin. Ground based wetland samples taken concurrently near Trinidad, Bolivia, gave a source signature of -56 ‰ ± 4 re-enforcing the likelihood that the atmospheric enhancements measured are related to the wetland emissions. For comparison, tropical wetlands measured at ground level during a recent Ugandan and Zambian campaign gave heavier δ<sup>13</sup>C<sub>CH4</sub> isotopic source signatures of -50 to -54 ‰. Based on this snap shot study, flux estimations suggest that the Bolivian wetlands could be emitting ~10mg CH<sub>4</sub> m<sup>-2 </sup>h<sup>-1</sup>. The observed mole fractions will be compared to model simulations to determine how well the Bolivian wetland methane fluxes are represented.</p>

scholarly journals Natural and anthropogenic methane fluxes in Eurasia: a meso-scale quantification by generalized atmospheric inversion

2014 ◽  
Vol 11 (10) ◽  
pp. 14587-14637 ◽  
Author(s):  
A. Berchet ◽  
I. Pison ◽  
F. Chevallier ◽  
J.-D. Paris ◽  
P. Bousquet ◽  
...  
Keyword(s):  
Atmospheric Transport ◽  
Region Of Interest ◽  
Methane Emissions ◽  
Surface Fluxes ◽  
Atmospheric Methane ◽  
Mixing Ratios ◽  
Methane Fluxes ◽  
Meso Scale ◽  
Atmospheric Inversion

Abstract. Eight surface observation sites providing quasi-continuous measurements of atmospheric methane mixing ratios have been operated since the mid-2000's in Siberia. For the first time in a single work, we assimilate all of these in situ data in an atmospheric inversion. Our objective is to quantify methane surface fluxes from anthropogenic and wetland sources at the meso-scale in the Siberian Lowlands for the year 2010. To do so, we first inquire into the way the inversion uses the observations and the fluxes are constrained by the observation sites. As atmospheric inversions at the meso-scale suffer from mis-quantified sources of uncertainties, we follow recent innovations in inversion techniques and use a new inversion approach which quantifies the uncertainties more objectively than the previous inversions. We find that, due to errors in the representation of the atmospheric transport and redundant pieces of information, only one observation every few days is found valuable by the inversion. The remaining high-resolution signals are representative of very local emission patterns. An analysis of the use of information by the inversion also reveals that the observation sites constrain methane emissions within a radius of 500 km. More observation sites are necessary to constrain the whole Siberian Lowlands. Still, the fluxes within the constrained areas are quantified with objectified uncertainties. At the end, the tolerance intervals for posterior methane fluxes are of roughly 20% (resp. 50%) of the fluxes for anthropogenic (resp. wetland) sources. About 50–70% of emissions are constrained by the inversion on average on an annual basis. Extrapolating the figures on the constrained areas to the whole Siberian Lowlands, we find a regional methane budget of 5–28 Tg CH4 for the year 2010, i.e. 1–5% of the global methane emissions. As very few in situ observations are available in the region of interest, observations of methane total columns from the Greenhouse Gas Observing SATellite (GOSAT) are used for the evaluation of the inversion results, but they exhibit marginal signal from the fluxes within the region of interest.

scholarly journals Characterisation of interferences to in-situ observations of δ<sup>13</sup>CH<sub>4</sub> and C<sub>2</sub>H<sub>6</sub> when using a Cavity Ring Down Spectrometer at industrial sites

2016 ◽  
Author(s):  
Sabina Assan ◽  
Alexia Baudic ◽  
Ali Guemri ◽  
Philippe Ciais ◽  
Valerie Gros ◽  
...  
Keyword(s):  
Natural Gas ◽  
Radiative Forcing ◽  
Industrial Revolution ◽  
Near Infrared ◽  
Isotope Analysis ◽  
Isotopic Signature ◽  
Atmospheric Methane ◽  
Ambient Conditions ◽  
Identification Methods ◽  
Mixing Ratios

Abstract. The increase of atmospheric methane (CH4) is the second largest contributor to the increased radiative forcing since the industrial revolution. Natural gas extraction and distribution is associated with CH4 leaks of uncertain magnitude that has spurred interest for developing new methods to measure them. Using a CRDS instrument we evaluate two methane identification methods commonly used to better constrain emission estimates from natural gas leaks, namely stable isotope analysis and the ethane: methane ratio (C2H6 : CH4). Recently it has come to light that CRDS measurements of δ13CH4 and C2H6 in the near infrared spectral domain are subject to cross sensitivities due to absorption from multiple gases. These sensitivities translate into biases in the retrieval of δ13CH4 and C2H6 concentrations in air samples, and should thus be accounted for during data processing. Here we present extensive laboratory tests using two CRDS instruments to characterize their cross sensitivities and propose corrections to calculate unbiased δ13CH4 and C2H6. Methane isotopic measurements were found to be subject to interference from elevated C2H6 concentrations (a secondary component in many natural gas types) resulting in heavier δ13CH4 by +23.5 ‰ per ppm C2H6 / ppm CH4. Measured C2H6 is subject to absorption interference from a number of other trace gases, the predominant being H2O (with an average linear sensitivity of 0.9 ppm C2H6 per % H2O in ambient conditions, meaning that the presence of H2O causes the inference of too high C2H6 mixing ratios if no correction is applied). Yet, this sensitivity was found to be discontinuous with a strong hysteresis effect. Throughout the range of C2H6 concentrations measured in this study (0–5 ppm C2H6), both CRDS instruments consistently measure concentrations double that reported by a GC, thus we have calculated a calibration factor of 0.5. To demonstrate the significance of the corrections we test the source identification methods on air measured at a natural gas compressor station. The presence of C2H6 in gas emissions at an average level of 0.3 ppm was found to shift the isotopic signature by 2.5 ‰. We find that after correction and calibration the average C2H6 : CH4 ratio shifts by +0.06. These results indicate that when using such a CRDS instrument in conditions of elevated C2H6 for CH4 source determination it is imperative to account for the biases discussed within this study.

scholarly journals Long-term O<sub>3</sub>–precursor relationships in Hong Kong: field observation and model simulation

2017 ◽  
Vol 17 (18) ◽  
pp. 10919-10935 ◽  
Author(s):  
Yu Wang ◽  
Hao Wang ◽  
Hai Guo ◽  
Xiaopu Lyu ◽  
Hairong Cheng ◽  
...  
Keyword(s):  
Hong Kong ◽  
Model Simulation ◽  
Ground Level ◽  
Effective Control ◽  
Photochemical Pollution ◽  
Mixing Ratios ◽  
The Past ◽  
Total Volatile Organic Compounds

Abstract. Over the past 10 years (2005–2014), ground-level O3 in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e. nitrogen oxides (NOx =  NO + NO2), total volatile organic compounds (TVOCs), and carbon monoxide (CO). To explain the contradictory phenomena, an observation-based box model (OBM) coupled with CB05 mechanism was applied in order to understand the influence of both locally produced O3 and regional transport. The simulation of locally produced O3 showed an increasing trend in spring, a decreasing trend in autumn, and no changes in summer and winter. The O3 increase in spring was caused by the net effect of more rapid decrease in NO titration and unchanged TVOC reactivity despite decreased TVOC mixing ratios, while the decreased local O3 formation in autumn was mainly due to the reduction of aromatic VOC mixing ratios and the TVOC reactivity and much slower decrease in NO titration. However, the decreased in situ O3 formation in autumn was overridden by the regional contribution, resulting in elevated O3 observations. Furthermore, the OBM-derived relative incremental reactivity indicated that the O3 formation was VOC-limited in all seasons, and that the long-term O3 formation was more sensitive to VOCs and less to NOx and CO in the past 10 years. In addition, the OBM results found that the contributions of aromatics to O3 formation decreased in all seasons of these years, particularly in autumn, probably due to the effective control of solvent-related sources. In contrast, the contributions of alkenes increased, suggesting a continuing need to reduce traffic emissions. The findings provide updated information on photochemical pollution and its impact in Hong Kong.

Exploring the variation in ecosystem scale methane fluxes and its drivers within a boreal mire complex

2021 ◽  
Author(s):  
Koffi Dodji Noumonvi ◽  
Joshua L. Ratcliffe ◽  
Mats Öquist ◽  
Mats B. Nilsson ◽  
Matthias Peichl
Keyword(s):  
Eddy Covariance ◽  
Land Surface ◽  
Chemical Properties ◽  
Growing Season ◽  
Small Scale ◽  
Atmospheric Methane ◽  
Flux Footprint ◽  
Growing Season Length ◽  
Methane Fluxes ◽  
Northern Peatlands

&lt;p&gt;Northern peatlands cover a small fraction of the earth&amp;#8217;s land surface, and yet they are one of the most important natural sources of atmospheric methane. With climate change causing rising temperatures, changes in water balance and increased growing season length, peatland contribution to atmospheric methane concentration is likely to increase, justifying the increased attention given to northern peatland methane dynamics. Northern peatlands often occur as heterogeneous complexes characterized by hydromorphologically distinct features from &lt; 1 m&amp;#178; to tens of km&amp;#178;, with differing physical, hydrological and chemical properties. The more commonly understood small-scale variation between hummocks, lawns and hollows has been well explored using chamber measurements. Single tower eddy covariance measurements, with a typical 95% flux footprint of &lt; 0.5 km&amp;#178;, have been used to assess the ecosystem scale methane exchange. However, how representative single tower flux measurements are of an entire mire complex is not well understood. To address this knowledge gap, the present study takes advantage of a network of four eddy covariance towers located less than 3 km apart at four mires within a typical boreal mire complex in northern Sweden. The variation of methane fluxes and its drivers between the four sites will be explored at different temporal scales, i.e. half-hourly, daily and at a growing-season scale.&lt;/p&gt;

scholarly journals An Optimized Snowmelt Lysimeter System for Monitoring Melt Rates and Collecting Samples for Stable Water Isotope Analysis

2019 ◽  
Vol 67 (1) ◽  
pp. 20-31 ◽  
Author(s):  
Andrea Rücker ◽  
Massimiliano Zappa ◽  
Stefan Boss ◽  
Jana von Freyberg
Keyword(s):  
Isotopic Composition ◽  
Isotope Analysis ◽  
Ground Level ◽  
Isotopic Signature ◽  
Small Scale ◽  
Spatial And Temporal Variability ◽  
Environmental Tracers ◽  
Hydrograph Separation ◽  
Stable Water Isotopes ◽  
Restricted Volume

Abstract The contribution of snow meltwater to catchment streamflow can be quantified through hydrograph separation analyses for which stable water isotopes (18O, 2H) are used as environmental tracers. For this, the spatial and temporal variability of the isotopic composition of meltwater needs to be captured by the sampling method. This study compares an optimized snowmelt lysimeter system and an unheated precipitation collector with focus on their ability to capture snowmelt rates and the isotopic composition of snowmelt. The snowmelt lysimeter system consists of three individual unenclosed lysimeters at ground level with a surface of 0.14 m2 each. The unheated precipitation collector consists of a 30 cm-long, extended funnel with its orifice at 2.3 m above ground. Daily snowmelt samples were collected with both systems during two snowfall-snowmelt periods in 2016. The snowmelt lysimeter system provided more accurate measurements of natural melt rates and allowed for capturing the small-scale variability of snowmelt process at the plot scale, such as lateral meltwater flow from the surrounding snowpack. Because of the restricted volume of the extended funnel, daily melt rates from the unheated precipitation collector were up to 43% smaller compared to the snowmelt lysimeter system. Overall, both snowmelt collection methods captured the general temporal evolution of the isotopic signature in snowmelt.

scholarly journals Development and application of a new mobile LOPAP instrument for the measurement of HONO altitude profiles in the planetary boundary layer

2009 ◽  
Vol 2 (4) ◽  
pp. 2027-2054 ◽  
Author(s):  
R. Häseler ◽  
T. Brauers ◽  
F. Holland ◽  
A. Wahner
Keyword(s):  
Nitrous Acid ◽  
Ground Level ◽  
Concentration Profiles ◽  
Mixing Ratio ◽  
Above Ground Level ◽  
Mixing Ratios ◽  
New Instrument ◽  
Mobile Measurements ◽  
Southwest Germany ◽  
Absorption Technique

Abstract. The LOPAP (long path absorption) technique has been shown to be very sensitive for the detection of nitrous acid (HONO) in the atmosphere. However, current instruments were mainly built for ground based applications. Therefore, we designed a new LOPAP instrument to be more versatile for mobile measurements and to meet the requirements for airborne application. The detection limit of the new instrument is below 1 ppt at a time resolution of 5 to 7 min. As a first test, the instrument was successfully employed during the ZEPTER-1 campaign in July 2007 on board of the Zeppelin NT airship. During 15 flights on six days we measured HONO concentration profiles over southwest Germany, predominantly in the range between 100 m and 650 m above ground level. On average, a mixing ratio of 34 ppt was observed, almost independently of height. Within a econd campaign, ZEPTER-2 in fall 2008, higher HONO mixing ratios were observed in the Lake Constance area.

scholarly journals No detectable aerobic methane efflux from plant material, nor from adsorption/desorption processes

2008 ◽  
Vol 5 (6) ◽  
pp. 1551-1558 ◽  
Author(s):  
M. U. F. Kirschbaum ◽  
A. Walcroft
Keyword(s):  
Zea Mays ◽  
High Surface ◽  
High Surface Area ◽  
Atmospheric Methane ◽  
Plant Materials ◽  
Methane Fluxes ◽  
Detached Leaves ◽  
Filter Papers ◽  
Adsorption Desorption ◽  
Methane Efflux

Abstract. In early 2006, Keppler et al. (Nature, 439:187–191) reported a novel finding that plant leaves, and even simple organic materials, can release methane under aerobic conditions. We investigated here whether the reported methane release might simply arise from methane desorption from sample surfaces after prior exposure to higher methane concentrations. We exposed standard cellulose filter papers (i.e. organic material with a high surface area) to atmospheric methane concentration and then transferred them to a low-methane atmosphere. Our results suggest that any desorption flux was extremely small (−0.0001±0.0019 ngCH4 kgDW−1 s−1) and would play no quantitatively significant role in modifying any measured methane fluxes. We also incubated fresh detached leaves of several species and intact Zea mays seedlings under aerobic and low-light conditions. After correcting for a small measured methane influx into empty chambers, measured rates of methane emission by plant materials were zero or, at most, very small, ranging from −0.25±1.1 ngCH4 kgDW−1 s−1 for Zea mays seedlings to 0.10±0.08 ngCH4 kgDW−1 s−1 for a mixture of freshly detached grasses. These rates were much smaller than the rates originally reported by Keppler et al. (2006).

scholarly journals Low levels of nitryl chloride at ground level: nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia

2018 ◽  
Vol 18 (9) ◽  
pp. 6293-6315 ◽  
Author(s):  
Hans D. Osthoff ◽  
Charles A. Odame-Ankrah ◽  
Youssef M. Taha ◽  
Travis W. Tokarek ◽  
Corinne L. Schiller ◽  
...  
Keyword(s):  
British Columbia ◽  
Nitrogen Oxides ◽  
Ground Level ◽  
Ambient Air ◽  
Data Set ◽  
Mixing Ratios ◽  
Nitryl Chloride ◽  
Short Period ◽  
Lower Fraser Valley ◽  
Fraser Valley

Abstract. The nocturnal nitrogen oxides, which include the nitrate radical (NO3), dinitrogen pentoxide (N2O5), and its uptake product on chloride containing aerosol, nitryl chloride (ClNO2), can have profound impacts on the lifetime of NOx (= NO + NO2), radical budgets, and next-day photochemical ozone (O3) production, yet their abundances and chemistry are only sparsely constrained by ambient air measurements. Here, we present a measurement data set collected at a routine monitoring site near the Abbotsford International Airport (YXX) located approximately 30 km from the Pacific Ocean in the Lower Fraser Valley (LFV) on the west coast of British Columbia. Measurements were made from 20 July to 4 August 2012 and included mixing ratios of ClNO2, N2O5, NO, NO2, total odd nitrogen (NOy), O3, photolysis frequencies, and size distribution and composition of non-refractory submicron aerosol (PM1). At night, O3 was rapidly and often completely removed by dry deposition and by titration with NO of anthropogenic origin and unsaturated biogenic hydrocarbons in a shallow nocturnal inversion surface layer. The low nocturnal O3 mixing ratios and presence of strong chemical sinks for NO3 limited the extent of nocturnal nitrogen oxide chemistry at ground level. Consequently, mixing ratios of N2O5 and ClNO2 were low (< 30 and < 100 parts-per-trillion by volume (pptv) and median nocturnal peak values of 7.8 and 7.9 pptv, respectively). Mixing ratios of ClNO2 frequently peaked 1–2 h after sunrise rationalized by more efficient formation of ClNO2 in the nocturnal residual layer aloft than at the surface and the breakup of the nocturnal boundary layer structure in the morning. When quantifiable, production of ClNO2 from N2O5 was efficient and likely occurred predominantly on unquantified supermicron-sized or refractory sea-salt-derived aerosol. After sunrise, production of Cl radicals from photolysis of ClNO2 was negligible compared to production of OH from the reaction of O(1D) + H2O except for a short period after sunrise.

scholarly journals In situ measurements of isoprene and monoterpenes within a south-east Asian tropical rainforest

2011 ◽  
Vol 11 (14) ◽  
pp. 6971-6984 ◽  
Author(s):  
C. E. Jones ◽  
J. R. Hopkins ◽  
A. C. Lewis
Keyword(s):  
Tropical Rainforest ◽  
East Asian ◽  
Ground Level ◽  
Ambient Air ◽  
Tropical Rainforests ◽  
Light Conditions ◽  
Mixing Ratios ◽  
Volatile Carbon ◽  
Malaysian Borneo

Abstract. Biogenic volatile organic compounds (BVOCs) emitted from tropical rainforests comprise a substantial fraction of global atmospheric VOC emissions, however there are only relatively limited measurements of these species in tropical rainforest regions. We present observations of isoprene, α-pinene, camphene, Δ-3-carene, γ-terpinene and limonene, as well as oxygenated VOCs (OVOCs) of biogenic origin such as methacrolein, in ambient air above a tropical rainforest in Malaysian Borneo during the Oxidant and Particle Photochemical Processes above a south-east Asian tropical rainforest (OP3) project in 2008. Daytime composition was dominated by isoprene, with an average mixing ratio of the order of ~1 ppb. γ-terpinene, limonene and camphene were the most abundant monoterpenes, with average daytime mixing ratios of 102, 71 and 66 ppt respectively, and with an average monoterpene toisoprene ratio of 0.3 during sunlit hours, compared to 2.0 at night. Limonene and camphene abundances were seen to be related to both temperature and light conditions. In contrast, γ-terpinene emission continued into the late afternoon/evening, under relatively low temperature and light conditions. The contributions of isoprene, monoterpenes and other classes of VOC to the volatile carbon budget and OH reactivity have been summarised for this rainforest location. We observe good agreement between surface and aircraft measurements of boundary layer isoprene and methacrolein above the natural rainforest, suggesting that the ground-level observations are broadly representative of isoprene emissions from this region.

scholarly journals Methane and Global Environmental Change

2018 ◽  
Vol 43 (1) ◽  
pp. 165-192 ◽  
Author(s):  
Dave S. Reay ◽  
Pete Smith ◽  
Torben R. Christensen ◽  
Rachael H. James ◽  
Harry Clark
Keyword(s):  
Climate Change ◽  
Environmental Change ◽  
Industrial Revolution ◽  
Net Primary Production ◽  
Global Climate ◽  
Global Environmental Change ◽  
Climate Change Policy ◽  
Climate Feedback ◽  
Atmospheric Methane ◽  
Methane Fluxes

Global atmospheric methane concentrations have continued to rise in recent years, having already more than doubled since the Industrial Revolution. Further environmental change, especially climate change, in the twenty-first century has the potential to radically alter global methane fluxes. Importantly, changes in temperature, precipitation, and net primary production may induce positive climate feedback effects in dominant natural methane sources such as wetlands, soils, and aquatic ecosystems. Anthropogenic methane sources may also be impacted, with a risk of enhanced emissions from the energy, agriculture, and waste sectors. Here, we review the global sources of methane, the trends in fluxes by source and sector, and their possible evolution in response to future environmental change. We discuss ongoing uncertainties in flux estimation and projection, and highlight the great potential for multisector methane mitigation as part of wider global climate change policy.

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