scholarly journals Chemical sensor resolution requirements for near-surface measurements of turbulent fluxes

2011 ◽  
Vol 11 (11) ◽  
pp. 5263-5275 ◽  
Author(s):  
M. D. Rowe ◽  
C. W. Fairall ◽  
J. A. Perlinger
Keyword(s):  
Eddy Covariance ◽  
Field Experiments ◽  
Chemical Sensor ◽  
Flux Measurement ◽  
Similarity Function ◽  
Atmospheric Parameter ◽  
Transfer Velocity ◽  
Surface Exchange ◽  
Near Surface ◽  
Sensor Resolution

Abstract. Businger and Delany (1990) presented an approach to estimate the sensor resolution required to limit the contribution of the uncertainty in the chemical concentration measurement to uncertainty in the flux measurement to 10 % for eddy covariance, gradient, and relaxed eddy accumulation flux measurement methods. We describe an improvement to their approach to estimate required sensor resolution for the covariance method, and include disjunct eddy covariance. In addition, we provide data to support selection of a form for the dimensionless scalar standard deviation similarity function based on observations of the variance of water vapor fluctuations from recent field experiments. We also redefine the atmospheric parameter of Businger and Delany in a more convenient, dimensionless form. We introduce a "chemical parameter" based on transfer velocity parameterizations. Finally, we provide examples in which the approach is applied to measurement of carbon dioxide, dimethylsulfide, and hexachlorobenzene fluxes over water. The information provided here will be useful to plan field measurements of atmosphere-surface exchange fluxes of trace gases.

scholarly journals Chemical sensor resolution requirements for near-surface measurements of turbulent fluxes

2010 ◽  
Vol 10 (10) ◽  
pp. 24409-24433 ◽  
Author(s):  
M. D. Rowe ◽  
C. W. Fairall ◽  
J. A. Perlinger
Keyword(s):  
Field Experiments ◽  
Chemical Sensor ◽  
Flux Measurement ◽  
Similarity Function ◽  
Atmospheric Parameter ◽  
Gas Transfer ◽  
Piston Velocity ◽  
Surface Exchange ◽  
Near Surface ◽  
Sensor Resolution

Abstract. Businger and Delany (1990) presented an approach to estimate the sensor resolution required to limit the contribution of the uncertainty in the chemical concentration measurement to the flux measurement uncertainty to 10% for eddy covariance, gradient, and relaxed eddy accumulation flux measurement methods. We describe an improvement to their approach to estimate required resolution for the covariance method. In addition, we provide data to support selection of a form for the dimensionless scalar standard deviation similarity function based on observations of the variance of water vapor fluctuations from recent field experiments. We also redefine the atmospheric parameter of Businger and Delany in a more convenient, dimensionless form. To make the expression convenient for gas transfer applications, we introduce a "chemical parameter" based on the gas transfer (piston) velocity. Finally, we provide examples in which the approach is applied to measurement of carbon dioxide, dimethylsulfide, and hexachlorobenzene fluxes. The information provided here will be useful to plan field measurements of atmosphere-surface exchange fluxes of trace gases.

scholarly journals Eddy covariance flux measurements of pollutant gases in urban Mexico City

2009 ◽  
Vol 9 (19) ◽  
pp. 7325-7342 ◽  
Author(s):  
E. Velasco ◽  
S. Pressley ◽  
R. Grivicke ◽  
E. Allwine ◽  
T. Coons ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Mexico City ◽  
Atmospheric Chemistry ◽  
Anthropogenic Activities ◽  
Flux Measurement ◽  
Proton Transfer Reaction ◽  
Surface Exchange ◽  
Emissions Inventory ◽  
Flux Measurements ◽  
Local Emissions

Abstract. Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded local emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The results show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not reported in the mobile emissions inventory.

scholarly journals Eddy covariance flux measurements of pollutant gases in urban Mexico City

2009 ◽  
Vol 9 (2) ◽  
pp. 7991-8034 ◽  
Author(s):  
E. Velasco ◽  
S. Pressley ◽  
R. Grivicke ◽  
E. Allwine ◽  
T. Coons ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Mexico City ◽  
Atmospheric Chemistry ◽  
Anthropogenic Activities ◽  
Flux Measurement ◽  
Proton Transfer Reaction ◽  
Surface Exchange ◽  
Emissions Inventory ◽  
Flux Measurements ◽  
Residential District

Abstract. Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The data show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not present in the mobile emissions inventory.

scholarly journals Correction of Eddy Covariance Based Crop ET Considering the Heat Flux Source Area

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 281
Author(s):  
Stuart L. Joy ◽  
José L. Chávez
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Agricultural Land ◽  
Flux Measurement ◽  
Source Area ◽  
Mean Bias Error ◽  
Bias Error ◽  
Crop Water ◽  
The Past ◽  
Measurement Results

Eddy covariance (EC) systems are being used to measure sensible heat (H) and latent heat (LE) fluxes in order to determine crop water use or evapotranspiration (ET). The reliability of EC measurements depends on meeting certain meteorological assumptions; the most important of such are horizontal homogeneity, stationarity, and non-advective conditions. Over heterogeneous surfaces, the spatial context of the measurement must be known in order to properly interpret the magnitude of the heat flux measurement results. Over the past decades, there has been a proliferation of ‘heat flux source area’ (i.e., footprint) modeling studies, but only a few have explored the accuracy of the models over heterogeneous agricultural land. A composite ET estimate was created by using the estimated footprint weights for an EC system in the upwind corner of four fields and separate ET estimates from each of these fields. Three analytical footprint models were evaluated by comparing the composite ET to the measured ET. All three models performed consistently well, with an average mean bias error (MBE) of about −0.03 mm h−1 (−4.4%) and root mean square error (RMSE) of 0.09 mm h−1 (10.9%). The same three footprint models were then used to adjust the EC-measured ET to account for the fraction of the footprint that extended beyond the field of interest. The effectiveness of the footprint adjustment was determined by comparing the adjusted ET estimates with the lysimetric ET measurements from within the same field. This correction decreased the absolute hourly ET MBE by 8%, and the RMSE by 1%.

scholarly journals Microanchored borehole fiber optics allows strain profiling of the shallow subsurface

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Cheng-Cheng Zhang ◽  
Bin Shi ◽  
Song Zhang ◽  
Kai Gu ◽  
Su-Ping Liu ◽  
...  
Keyword(s):  
Fiber Optics ◽  
Field Experiments ◽  
Fiber Optic ◽  
Strain Sensing ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Buried Cables ◽  
Capacity Theory ◽  
Confining Pressures ◽  
Strain Determination

AbstractVertical deformation profiles of subterranean geological formations are conventionally measured by borehole extensometry. Distributed strain sensing (DSS) paired with fiber-optic cables installed in the ground opens up possibilities for acquiring high-resolution static and quasistatic strain profiles of deforming strata, but it is currently limited by reduced data quality due to complicated patterns of interaction between the buried cables and their surroundings, especially in upper soil layers under low confining pressures. Extending recent DSS studies, we present an improved approach using microanchored fiber-optic cables—designed to optimize ground-to-cable coupling at the near surface—for strain determination along entire lengths of vertical boreholes. We proposed a novel criterion for soil–cable coupling evaluation based on the geotechnical bearing capacity theory. We applied this enhanced methodology to monitor groundwater-related vertical motions in both laboratory and field experiments. Corroborating extensometer recordings, acquired simultaneously, validated fiber optically determined displacements, suggesting microanchored DSS as an improved means for detecting and monitoring shallow subsurface strain profiles.

scholarly journals Micrometeorological measurement of hexachlorobenzene and polychlorinated biphenyl compound air-water gas exchange in Lake Superior and comparison to model predictions

2012 ◽  
Vol 12 (10) ◽  
pp. 4607-4617 ◽  
Author(s):  
M. D. Rowe ◽  
J. A. Perlinger
Keyword(s):  
Water Exchange ◽  
Polychlorinated Biphenyl ◽  
Lake Superior ◽  
Estimation Method ◽  
Internal Boundary ◽  
Transfer Model ◽  
Atmospheric Concentration ◽  
Transfer Velocity ◽  
Near Surface ◽  
Flux Measurements

Abstract. Air-water exchange fluxes of persistent, bioaccumulative and toxic (PBT) substances are frequently estimated using the Whitman two-film (W2F) method, but micrometeorological flux measurements of these compounds over water are rarely attempted. We measured air-water exchange fluxes of hexachlorobenzene (HCB) and polychlorinated biphenyls (PCBs) on 14 July 2006 in Lake Superior using the modified Bowen ratio (MBR) method. Measured fluxes were compared to estimates using the W2F method, and to estimates from an Internal Boundary Layer Transport and Exchange (IBLTE) model that implements the NOAA COARE bulk flux algorithm and gas transfer model. We reveal an inaccuracy in the estimate of water vapor transfer velocity that is commonly used with the W2F method for PBT flux estimation, and demonstrate the effect of use of an improved estimation method. Flux measurements were conducted at three stations with increasing fetch in offshore flow (15, 30, and 60 km) in southeastern Lake Superior. This sampling strategy enabled comparison of measured and predicted flux, as well as modification in near-surface atmospheric concentration with fetch, using the IBLTE model. Fluxes estimated using the W2F model were compared to fluxes measured by MBR. In five of seven cases in which the MBR flux was significantly greater than zero, concentration increased with fetch at 1-m height, which is qualitatively consistent with the measured volatilization flux. As far as we are aware, these are the first reported ship-based micrometeorological air-water exchange flux measurements of PCBs.

scholarly journals Air–surface exchange of gaseous mercury over permafrost soil: an investigation at a high-altitude (4700 m a.s.l.) and remote site in the central Qinghai-Tibet Plateau

2016 ◽  
Author(s):  
Zhijia Ci ◽  
Fei Peng ◽  
Xian Xue ◽  
Xiaoshan Zhang
Keyword(s):  
High Altitude ◽  
Field Experiments ◽  
Tibet Plateau ◽  
Permafrost Soil ◽  
Remote Site ◽  
Water Addition ◽  
Surface Exchange ◽  
Entire Study ◽  
Gaseous Mercury ◽  
Qinghai Tibet Plateau

Abstract. The pattern of air–surface gaseous mercury (mainly Hg(0)) exchange in the Qinghai-Tibet Plateau (QTP) may be unique because this region is characterized by low temperature, great temperature variation, intensive solar radiation, and pronounced freeze-thaw process of permafrost soils. However, air–surface Hg(0) flux in the QTP is poorly investigated. In this study, we performed filed measurements and controlled field experiments with dynamic flux chambers technique to examine the flux, temporal variation and influencing factors of air–surface Hg(0) exchange at a high-altitude (4700 m a.s.l.) and remote site in the central QTP. The results of field measurements showed that surface soils were net emission source of Hg(0) in the entire study. Hg(0) flux showed remarkable seasonality with net high emission in the warm campaigns and net low deposition in winter campaign, and also showed the diurnal pattern with emission in daytime and deposition in nighttime, especially on days without precipitation. Rainfall events on the dry soils induced large and immediate increase in Hg(0) emission. Snowfall events did not induce the pulse of Hg(0) emission, but snow melt resulted in the immediate increase in Hg(0) emission. Daily Hg(0) fluxes on rainy or snowy days were higher than those of days without precipitation. Controlled field experiments suggested that water addition to dry soils significantly increased Hg(0) emission both in short and relatively long timescales, and also showed that UV radiation was primarily attributed to Hg(0) emission in the daytime. Our findings imply that a warm climate and environmental change could facilitate Hg release from the permafrost terrestrial ecosystem in the QTP.

scholarly journals Field Measurements of Surface and Near-Surface Turbulence in the Presence of Breaking Waves

2015 ◽  
Vol 45 (4) ◽  
pp. 943-965 ◽  
Author(s):  
Peter Sutherland ◽  
W. Kendall Melville
Keyword(s):  
Field Experiments ◽  
North Pacific Ocean ◽  
Large Fraction ◽  
Field Measurements ◽  
Breaking Waves ◽  
Sea Surface ◽  
Near Surface ◽  
Wave Energy Dissipation ◽  
Eddy Simulation ◽  
The North

AbstractWave breaking removes energy from the surface wave field and injects it into the upper ocean, where it is dissipated by viscosity. This paper presents an investigation of turbulent kinetic energy (TKE) dissipation beneath breaking waves. Wind, wave, and turbulence data were collected in the North Pacific Ocean aboard R/P FLIP, during the ONR-sponsored High Resolution Air-Sea Interaction (HiRes) and Radiance in a Dynamic Ocean (RaDyO) experiments. A new method for measuring TKE dissipation at the sea surface was combined with subsurface measurements to allow estimation of TKE dissipation over the entire wave-affected surface layer. Near the surface, dissipation decayed with depth as z−1, and below approximately one significant wave height, it decayed more quickly, approaching z−2. High levels of TKE dissipation very near the sea surface were consistent with the large fraction of wave energy dissipation attributed to non-air-entraining microbreakers. Comparison of measured profiles with large-eddy simulation results in the literature suggests that dissipation is concentrated closer to the surface than previously expected, largely because the simulations did not resolve microbreaking. Total integrated dissipation in the water column agreed well with dissipation by breaking for young waves, (where cm is the mean wave frequency and is the atmospheric friction velocity), implying that breaking was the dominant source of turbulence in those conditions. The results of these extensive measurements of near-surface dissipation over three field experiments are discussed in the context of observations and ocean boundary layer modeling efforts by other groups.

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