Eddy Covariance Setup Research Articles

Bidirectional Turbulent Fluxes of Fog at a Subtropical Montane Cloud Forest Covering a Wide Size Range of Droplets

Size-resolved turbulent fluxes of fog droplets are investigated above a subtropical montane cloud forest in Taiwan. By integrating an aerosol spectrometer into an eddy-covariance set-up, we measure droplet number fluxes and liquid water fluxes in a size range of aerosol particles and droplets with diameters ranging from 0.25 {upmu }!mathrm{m} to 17.3 {upmu }!mathrm{m}. We find two flux-direction changes within this size range: a downward flux occurs for accumulation-mode aerosols of diameters between 0.25 {upmu }!mathrm{m} and 0.83 {upmu }!mathrm{m}, an upward flux occurs for hydrated aerosols with diameters between 1.1 {upmu }!mathrm{m} and 2.4 {upmu }!mathrm{m}, and a downward flux occurs again for activated fog droplets between diameters of 3 {upmu }!mathrm{m} and 17.3 {upmu }!mathrm{m}. The droplet size distributions can be modelled by a trimodal log-normal distribution, and the modes correlate with the different flux directions. The formation of the three modes and the establishment of the respective flux directions can be explained by combining the Köhler theory on the basis of measured ion concentrations in fog with the turbulent transport of droplets. Finally, from the combined analysis of droplet fluxes and size distributions, we infer relevant processes of droplet development and dissolving during various phases of the life cycles of the fog events.

Evapotranspiration over agroforestry sites in Germany

Abstract. In the past few years, the interest in growing crops and trees for bioenergy production has increased. One agricultural practice is the mixed cultivation of fast-growing trees and annual crops or perennial grasslands on the same piece of land, which is referred to as one type of agroforestry (AF). The inclusion of tree strips into the agricultural landscape has been shown – on the one hand – to lead to reduced wind speeds and higher carbon sequestration above ground and in the soil. On the other hand, concerns have been raised about increased water losses to the atmosphere via evapotranspiration (ET). Therefore, we hypothesise that short rotation coppice agroforestry systems have higher water losses to the atmosphere via ET compared to monoculture (MC) agriculture without trees. In order to test the hypothesis, the main objective was to measure the actual evapotranspiration of five AF systems in Germany and compare those to five monoculture systems in the close vicinity of the AF systems. We measured actual ET at five AF sites in direct comparison to five monoculture sites in northern Germany in 2016 and 2017. We used an eddy covariance energy balance (ECEB) set-up and a low-cost eddy covariance (EC-LC) set-up to measure actual ET over each AF and each MC system. We conducted direct eddy covariance (EC) measurement campaigns with approximately 4 weeks' duration for method validation. Results from the short-term measurement campaigns showed a high agreement between ETEC-LC and ETEC, indicated by slopes of a linear regression analysis between 0.86 and 1.3 (R2 between 0.7 and 0.94) across sites. Root mean square errors of LEEC-LC vs. LEEC (where LE is the latent heat flux) were half as small as LEECEB vs. LEEC, indicating a superior agreement of the EC-LC set-up with the EC set-up compared to the ECEB set-up. With respect to the annual sums of ET over AF and MC, we observed small differences between the two land uses. We interpret this as being an effect of compensating the small-scale differences in ET next to and in between the tree strips for ET measurements on the system scale. Most likely, the differences in ET rates next to and in between the tree strips are of the same order of magnitude, but of the opposite sign, and compensate each other throughout the year. Differences between annual sums of ET from the two methods were of the same order of magnitude as differences between the two land uses. Compared to the effect of land use and different methods on ET, we found larger mean evapotranspiration indices (∑ET/∑P) across sites for a drier than normal year (2016) compared to a wet year (2017). This indicates that we were able to detect differences in ET due to different ambient conditions with the applied methods, rather than the potentially small effect of AF on ET. We conclude that agroforestry has not resulted in an increased water loss to the atmosphere, indicating that agroforestry in Germany can be a land-use alternative to monoculture agriculture without trees.

Low-cost eddy covariance: a case study of evapotranspiration over agroforestry in Germany

Abstract. Heterogeneous land surfaces require multiple measurement units for spatially adequate sampling and representative fluxes. The complexity and cost of traditional eddy covariance (EC) set-ups typically limits the feasible number of sampling units. Therefore, new low-cost eddy covariance systems provide ideal opportunities for spatially replicated sampling. The aim of this study was to test the performance of a compact, low-cost pressure, temperature and relative humidity sensor for the application of evapotranspiration measurements by eddy covariance over agroforestry and conventional agriculture in Germany. We performed continuous low-cost eddy covariance measurements over agroforestry and conventional agriculture for reference at five sites across northern Germany over a period of 2 years from 2016 to 2017. We conducted side-by-side measurements using a roving enclosed-path eddy covariance set-up to assess the performance of the low-cost eddy covariance set-up. Evapotranspiration measured with low-cost eddy covariance compared well with fluxes from conventional eddy covariance. The slopes of linear regressions for evapotranspiration comparing low-cost and conventional eddy covariance set-ups ranged from 0.86 to 1.08 for 5 out of 10 sites, indicating a 14 % flux underestimation and a 8 % flux overestimation relative to the conventional eddy covariance set-up, respectively. Corresponding coefficients of determination, R2, ranged from 0.71 to 0.94 across sites. The root-mean-square error for differences between latent heat fluxes obtained by both set-ups were small compared to the overall flux magnitude, with a mean and standard deviation of 34.23±3.2 W m−2, respectively, across sites. The spectral response characteristics of the low-cost eddy covariance set-up were inferior to the eddy covariance set-up in the inertial sub-range of the turbulent spectrum. The water vapour flux co-spectrum of the low-cost eddy covariance set-up underestimated the theoretical slope of -4/3, stronger than the conventional eddy covariance set-up. This underestimation was mainly caused by the limited response time of the low-cost thermohygrometer being longer than 1 s. We conclude that low-cost eddy covariance sensors are an alternative to conventional eddy covariance sensors when, first, replicates are required and, second, the spatial variability of fluxes of the ecosystems of interest is larger than above-reported set-up-specific differences in fluxes.

Eddy covariance measurements of the dual-isotope composition of evapotranspiration

Measurements of the isotopic composition of water vapor (H2Ov) provide valuable insights into the hydrological cycle, whereas eddy covariance (EC) measurements are widely used to quantify biosphere-atmosphere exchange processes. Yet, the direct combination of water isotope approaches and the EC method remains technically challenging. Here, we present the first EC measurements of δ18O and δD of evapotranspiration (ET) over the full growing season of a beech forest in central Germany. This EC implementation is based on 2 Hz measurements of the mole fraction and isotopic composition of water vapor (CH2O,v, δD and δ18O) with a customized version of a commercially available water vapor isotope analyzer. The isotopic composition of ET showed a seasonal variability from −19 to 0‰ for δ18OET and from −140 to −25‰ for δDET. The setup-specific limitations of our measurements yield a mean bias of 0.03 mmol m−2 s−1 of the measured net water flux. Spectral and cospectral analysis showed that high-frequency dampening was less pronounced for our EC setup (which was equipped with heated tubing) than for the standard EC setup at this site. Thus, we conclude that direct EC measurements of the isotopic composition of ET are feasible for both, δ18OET and δDET. We propose that EC-based measurements of the isotopic composition of ET are feasible to improve our understanding of the hydrological cycle, especially where flux gradient methods show limited applicability. Our simultaneous measurements of δDET and δ18OET reveal the difference between transpiration-dominated and evaporation-dominated periods. This study highlights the potential of simultaneous measurements of δ18OET and δDET.

Performance Evaluation of an Integrated Open-Path Eddy Covariance System in a Cold Desert Environment

AbstractPerformance evaluation of an integrated eddy covariance (EC) instrument called the IRGASON, with a separated EC for reference, was conducted in a desert riparian Populus euphratica stand in the lower Tarim River basin in northwestern China. The separated EC consisted of an open-path gas analyzer and a sonic anemometer separated by 20 cm. The IRGASON integrates an open-path gas analyzer and a sonic anemometer into the same sensing volume, thus eliminating sensor separation in comparison to the traditional open-path EC setup. Integrating the infrared gas analyzer’s sensing head into the sensing volume of the sonic anemometer had negligible effects on wind speed and friction velocity observations of the IRGASON. Physiologically unreasonable daytime CO2 uptake was observed by both systems during the cold winter season (mean air temperature of −6.7°C), when the trees were dormant without any photosynthetic activities. The mean midday CO2 flux was −1.65 and −1.61 μmol m−2 s−1 for the IRGASON and the separated EC setup, respectively. No evidence was found for sensor self-heating as the cause of the apparent uptake CO2 flux. Instead, the uptake CO2 flux appeared to be an artifact of the spectroscopic effect of the IRGASON’s gas analyzer. After adjusting for this spectroscopic effect using a relationship with the sensible heat flux, the wintertime IRGASON CO2 flux became physiologically reasonable (mean value of −0.04 μmol m−2 s−1).

Impact of grazing on carbon dioxide exchanges in an intensively managed Belgian grassland

Given that the soil carbon (C) sequestration potential by grasslands can be used to partly mitigate the total greenhouse gas emissions of livestock production systems, a better understanding of the effects of management practices, and especially grazing, on grassland carbon dioxide (CO2) exchanges has become a major concern. This study aimed at quantifying grazing impact on CO2 fluxes measured by eddy covariance by using innovative data analyses and experiments. For that, we distinguished direct and indirect grazing impact. Indirect impact results from biomass consumption, excretion deposits and soil compaction by cattle that modify CO2 exchanges. Direct impact results from livestock CO2 emissions through respiration that add to total ecosystem respiration. For the indirect impact, the variation during periods with fixed stocking rate of gross primary productivity at light saturation (GPPmax) and normalized dark respiration (Rd,10) was analyzed. On average, GPPmax decreased during grazing periods and increased during non-grazing periods which could be explained by aboveground biomass reduction and re-growth, respectively. In addition, GPPmax variations were negatively correlated to grazing intensity (defined as the product of the stocking rate and the grazing duration). On the contrary, no significant evolution of Rd,10 was found during both grazing and non-grazing periods, probably due to a combination of opposing effects of grazing on the total ecosystem respiration components. The direct impact was emphasized through four specific designed confinement experiments. Each experiment extended over three successive days. On the first and third day, there was no cattle on the plot, while, on the second day, cattle were confined in the main wind direction area of the eddy covariance set-up to increase the stocking rate (≈26livestockunitsha−1). The average livestock CO2 emissions during confinement, FCO2,livestock, were deduced from the differences between half-hourly measurements taken at 24h interval with or without cattle and under similar environmental conditions. They were estimated to be 2.59±0.58kgClivestockunit−1d−1 on average. This result was corroborated by independent estimates based on the C ingested by cattle during confinement. Using an annual average stocking of 2livestockunitsha−1, we found that livestock CO2 emissions represent only 8% of this grassland annual total ecosystem respiration. To our knowledge, this study is the first to quantify both direct and indirect livestock contribution to CO2 fluxes exchanged at the ecosystem scale using the eddy covariance technique.

Fluxes of total reactive atmospheric nitrogen (ΣNr) using eddy covariance above arable land

ABSTRACTThe amount and timing of reactive nitrogen exchange between agricultural land and the atmosphere play a key role in evaluating ecosystem productivity and in addressing atmospheric nitrogen budgets and transport. With the recent development of the Total Reactive Atmospheric Nitrogen Converter (TRANC) apparatus, a methodology has been provided for continuous measurement of the sum of all airborne nitrogen containing species (ΣNr) allowing for diurnal and seasonal investigations. We present ΣNr concentration and net flux data from an 11-month field campaign conducted at an arable field using the TRANC system within an eddy-covariance setup. Clear diurnal patterns of both ΣNr concentrations and fluxes with significant dependencies on atmospheric stability and stomatal regulation were observed in the growing season. TRANC data were compared with monthly-averaged concentrations and dry deposition rates of selected Nr compounds using DELTA denuders and ensemble-averages of four inferential models, respectively. Similar seasonal trends were found for Nr concentrations from DELTA and TRANC measurements with values from the latter being considerably higher than those of DELTA denuders. The variability of the difference between these two systems could be explained by seasonally changing source locations of NOx contributions to the TRANC signal. As soil and vegetation Nr emissions to the atmosphere are generally not treated by inferential (dry deposition) models, TRANC data showed lower monthly deposition rates than those obtained from inferential modelling. Net ΣNr exchange was almost neutral (~0.072 kg N ha−1) at the end of the observation period. However, during most parts of the year, slight but permanent net ΣNr deposition was found. Our measurements demonstrate that fertilizer addition followed by substantial ΣNr emissions plays a crucial role in a site's annual atmospheric nitrogen budget. As long-term Nr measurements with high temporal resolution are usually cost and labour-intensive, field application of the TRANC helps improve the understanding of ecosystem functioning, atmospheric transport and revising definitions of ecosystem-specific critical loads at a relatively moderate operational cost level.

Four-year (2006–2009) eddy covariance measurements of CO<sub>2</sub> flux over an urban area in Beijing

Abstract. Long-term measurements of carbon dioxide flux (Fc) and the latent and sensible heat fluxes were performed using the eddy covariance (EC) method in Beijing, China over a 4-yr period in 2006–2009. The EC setup was installed at a height of 47 m on the Beijing 325-m meteorological tower in the northwest part of the city. Latent heat flux dominated the energy exchange between the urban surface and the atmosphere in summer, while sensible heat flux was the main component in the spring. Winter and autumn were two transition periods of the turbulent fluxes. The source area of Fc was highly heterogeneous, which consisted of buildings, parks, and highways. It was of interest to study of the temporal and spatial variability of Fc in this urban environment of a developing country. Both on diurnal and monthly scale, the urban surface acted as a net source for CO2 and downward fluxes were only occasionally observed. The diurnal pattern of Fc showed dependence on traffic and the typical two peak traffic patterns appeared in the diurnal cycle. Also Fc was higher on weekdays than on weekends due to the higher traffic volumes on weekdays. On seasonal scale, Fc was generally higher in winter than during other seasons likely due to domestic heating during colder months. Total annual average CO2 emissions from the neighborhood of the tower were estimated to be 4.90 kg C m−2 yr−1 over the 4-yr period. Total vehicle population was the most important factor controlling the inter-annual variability of Fc in this urban area.

TRANC – a novel fast-response converter to measure total reactive atmospheric nitrogen

Abstract. The input and loss of plant available nitrogen (reactive nitrogen: Nr) from/to the atmosphere can be an important factor for the productivity of ecosystems and thus for its carbon and greenhouse gas exchange. We present a novel converter for reactive nitrogen (TRANC: Total Reactive Atmospheric Nitrogen Converter), which offers the opportunity to quantify the sum of all airborne reactive nitrogen compounds (∑Nr) in high time resolution. The basic concept of the TRANC is the full conversion of all Nr to nitrogen monoxide (NO) within two reaction steps. Initially, reduced Nr compounds are being oxidised, and oxidised Nr compounds are thermally converted to lower oxidation states. Particulate Nr is being sublimated and oxidised or reduced afterwards. In a second step, remaining higher nitrogen oxides or those generated in the first step are catalytically converted to NO with carbon monoxide used as reduction gas. The converter is combined with a fast response chemiluminescence detector (CLD) for NO analysis and its performance was tested for the most relevant gaseous and particulate Nr species under both laboratory and field conditions. Recovery rates during laboratory tests for NH3 and NO2 were found to be 95 and 99%, respectively, and 97% when the two gases were combined. In-field longterm stability over an 11-month period was approved by a value of 91% for NO2. Effective conversion was also found for ammonium and nitrate containing particles. The recovery rate of total ambient Nr was tested against the sum of individual measurements of NH3, HNO3, HONO, NH4+, NO3−, and NOx using a combination of different well-established devices. The results show that the TRANC-CLD system precisely captures fluctuations in ∑Nr concentrations and also matches the sum of all individual Nr compounds measured by the different single techniques. The TRANC features a specific design with very short distance between the sample air inlet and the place where the thermal and catalytic conversions to NO occur. This assures a short residence time of the sample air inside the instrument, and minimises wall sorption problems of water soluble compounds. The fast response time (e-folding times of 0.30 to 0.35 s were found during concentration step changes) and high accuracy in capturing the dominant Nr species enables the converter to be used in an eddy covariance setup. Although a source attribution of specific Nr compounds is not possible, the TRANC is a new reliable tool for permanent measurements of the net ∑Nr flux between ecosystem and atmosphere at a relatively low maintenance and reasonable cost level allowing for diurnal, seasonal and annual investigations.

Eddy covariance measurements of CO 2 isotopologues with a quantum cascade laser absorption spectrometer

Stable isotope measurements of the biosphere–atmosphere CO 2 exchange can be used to constrain carbon budget estimates on different spatial and temporal scales. Eddy covariance (EC) measurements can provide a direct measure of the isotope flux ratio of CO 2 and thus indicate the ecosystem fingerprint on the isotope budget of the atmosphere. For the first time we report on EC flux measurements of stable CO 2 isotopologues over a forest canopy. We used a quantum cascade laser absorption spectrometer (QCLAS, Aerodyne Research Inc.) for the simultaneous measurement of 12CO 2, 13CO 2 and CO 18O isotopologue fluxes with a sampling rate of 10 Hz over the Lägeren mixed forest site in Switzerland during an intensive field campaign in 2008. The total CO 2 flux measured with the closed-path QCLAS matches well the half-hourly fluxes measured with a conventional open-path infrared gas analyzer ( R 2 = 0.988). The 18O isotope discrimination is strongly reduced after precipitation events, reflecting 18O isotope exchange of CO 2 with water in various water pools of the ecosystem. The 13CO 2/ 12CO 2 flux ratio is surprisingly constant on a diurnal timescale, but the substantial random noise in the half-hourly EC flux ratio puts a limit on resolving diurnal variations of only a few permil. Hence, we explore which component in our EC set-up is limiting the precision of the measured flux ratios. On the one hand we use data simulations to estimate the error contribution from the QCLAS instrument. On the other hand different EC data processing procedures are examined to quantify the uncertainty inherently associated with turbulent flux measurements and calculations. We show that the random error associated with EC data processing is of the same order of magnitude as the flux ratio uncertainty from the instrument precision. Therefore, a direct determination of ecosystem discrimination on hourly or diurnal time scales with the EC technique remains a challenge.

Spatial and temporal dynamics in eddy covariance observations of methane fluxes at a tundra site in northeastern Siberia

In the past two decades, the eddy covariance technique has been used for an increasing number of methane flux studies at an ecosystem scale. Previously, most of these studies used a closed path setup with a tunable diode laser spectrometer (TDL). Although this method worked well, the TDL has to be calibrated regularly and cooled with liquid nitrogen or a cryogenic system, which limits its use in remote areas. Recently, a new closed path technique has been introduced that uses off-axis integrated cavity output spectroscopy that does not require regular calibration or liquid nitrogen to operate and can thus be applied in remote areas. In the summer of 2008 and 2009, this eddy covariance technique was used to study methane fluxes from a tundra site in northeastern Siberia. The measured emissions showed to be very dependent on the fetch area, due to a large contrast in dry and wet vegetation in between wind directions. Furthermore, the observed short-and long-term variation of methane fluxes could be readily explained with a nonlinear model that used relationships with atmospheric stability, soil temperature, and water level. This model was subsequently extended to fieldwork periods preceding the eddy covariance setup and applied to evaluate a spatially integrated flux. The model result showed that average fluxes were 56.5, 48.7, and 30.4 nmol CH4 m(-2) s(-1) for the summers of 2007 to 2009. While previous models of the same type were only applicable to daily averages, the method described can be used on a much higher temporal resolution, making it suitable for gap filling. Furthermore, by partitioning the measured fluxes along wind direction, this model can also be used in areas with nonuniform terrain but nonetheless provide spatially integrated fluxes. (Less)

Field intercomparison of two optical analyzers for CH<sub>4</sub> eddy covariance flux measurements

Abstract. Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane exchange. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

Measurement of the Sensible Eddy Heat Flux Based on Spatial Averaging of Continuous Ground-Based Observations

Using the standard eddy-covariance (EC) method to quantify mass and energy exchange at a single location usually results in an underestimation of vertical eddy fluxes at the surface. In order to better understand the reasons for this underestimation, an experimental set-up is presented that is based on spatial averaging of air temperature data from a network of ground-based sensors over agricultural land. For eight days during the 34-day observational period in May and June 2007, additional contributions to the sensible heat flux of more than 50Wm−2 were measured in the lower surface layer by applying the spatial EC method as opposed to the standard temporal EC method. Smaller but still significant additional sensible heat fluxes were detected for four more days. The additional energy is probably transported in organised convective structures resulting in a mean vertical wind velocity unequal to zero at the tower location. The results show that convective transport contributes significantly to the surface energy budget for measurement heights as low as 2–3 m. Since these structures may be quasi-stationary, they can hardly be captured by a single-location measurement. The spatial EC set-up presented here is capable of quantifying contributions to the sensible heat flux from structures up to the scale of our spatial sensor network, which covered an area 3.5 × 3.5 km. For future experiments aiming at closing the energy balance, the spatial EC method should be employed to measure both the sensible and latent heat fluxes. Experimental determination of the horizontal advection of sensible and latent heat should also be considered, since such transport must occur due to convergence and divergence related to convection.

A compact and stable eddy covariance set-up for methane measurements using off-axis integrated cavity output spectroscopy

Abstract. A Fast Methane Analyzer (FMA) is assessed for its applicability in a closed path eddy covariance field set-up in a peat meadow. The FMA uses off-axis integrated cavity output spectroscopy combined with a highly specific narrow band laser for the detection of CH4 and strongly reflective mirrors to obtain a laser path length of 2–20×103 m. Statistical testing and a calibration experiment showed high precision (7.8×10−3 ppb) and accuracy (<0.30%) of the instrument, while no drift was observed. The instrument response time was determined to be 0.10 s. In the field set-up, the FMA is attached to a scroll pump and combined with a 3-axis ultrasonic anemometer and an open path infrared gas analyzer for measurements of carbon dioxide and water vapour. The power-spectra and co-spectra of the instruments were satisfactory for 10 Hz sampling rates. Due to erroneous measurements, spikes and periods of low turbulence the data series consisted for 26% of gaps. Observed CH4 fluxes consisted mainly of emission, showed a diurnal cycle, but were rather variable over. The average CH4 emission was 29.7 nmol m−2 s−1, while the typical maximum CH4 emission was approximately 80.0 nmol m−2 s−1 and the typical minimum flux was approximately 0.0 nmol m−2 s−1. The correspondence of the measurements with flux chamber measurements in the footprint was good and the observed CH4 emission rates were comparable with eddy covariance CH4 measurements in other peat areas. Additionally, three measurement techniques with lower sampling frequencies were simulated, which might give the possibility to measure CH4 fluxes without an external pump and save energy. Disjunct eddy covariance appeared to be the most reliable substitute for 10 Hz eddy covariance, while relaxed eddy accumulation gave reliable estimates of the fluxes over periods in the order of days or weeks.

Methanol and acetaldehyde fluxes over ryegrass

Oxygenated volatile organic compounds (OVOCs) play an active role in tropospheric chemistry but our knowledge concerning their release and ultimate fate is limited. However, the recent introduction of Proton Transfer Reaction Mass Spectrometry (PTRMS) has improved our capability to make direct field observations of OVOC mixing ratios and fluxes. We used PTRMS in an eddy covariance setup to measure selected OVOC exchange rates above a well-characterized agricultural plot in Northern Germany. In fall 2003, mixing ratios of methanol and acetaldehyde 2m above the field ranged from 1 to 10 and 0.4 to 2.1 ppb, respectively, well correlated with one another. Fluxes of both gases were followed for growing Italian ryegrass (Lolium multiflorum) over a significant portion of its life cycle. Diurnally fluctuating emissions of methanol and very small acetaldehyde fluxes were observed up to the cutting and removal of the grass. Methanol emissions were exponentially related to ambient temperatures and appeared to be higher during the grass’ rapid leaf area expansion and after a rain event. Acetaldehyde exchanges averaged over the whole period indicated very slow deposition. Our measurements confirm previous, similar results, as well as presumptions that grasses are comparatively low methanol emitters compared to non-grass species.