Eddy Covariance Measurements Highlight Sources of Nitrogen Oxide Emissions Missing from Inventories for Central London

Abstract. During March–June 2017 emissions of nitrogen oxides were measured via eddy covariance at the British Telecom Tower in central London, UK. Through the use of a footprint model the expected emissions were simulated from the spatially resolved National Atmospheric Emissions Inventory for 2017, and compared with the measured emissions. These simulated emissions were shown to underestimate measured emissions during the day time by a factor of 1.48, but they agreed well overnight. Furthermore, underestimations were spatially mapped and the areas around the measurement site responsible for differences in measured and simulated emissions inferred. It was observed that areas of higher traffic, such as major roads near national rail stations, showed the greatest underestimation by the simulated emissions. These discrepancies are partially attributed to a combination of the inventory not fully capturing traffic conditions in central London, and both spatial and temporal resolution of the inventory not fully describing the high heterogeneity of the urban centre. Understanding of this underestimation may further improved with longer measurement time series ,to better understand temporal variation, and improved temporal scaling factors, to better simulate sub-annual emissions.

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Spatially resolved flux measurements of NOx from London suggest significantly higher emissions than predicted by inventories

Faraday Discussions ◽

10.1039/c5fd00170f ◽

2016 ◽

Vol 189 ◽

pp. 455-472 ◽

Cited By ~ 20

Author(s):

Adam R. Vaughan ◽

James D. Lee ◽

Pawel K. Misztal ◽

Stefan Metzger ◽

Marvin D. Shaw ◽

...

Keyword(s):

Real World ◽

Road Traffic ◽

Measurement Data ◽

Time Of Day ◽

Atmospheric Emissions ◽

Emissions Inventory ◽

Spatially Resolved ◽

Road Traffic Emissions ◽

Flux Measurements ◽

Emissions Inventories

To date, direct validation of city-wide emissions inventories for air pollutants has been difficult or impossible. However, recent technological innovations now allow direct measurement of pollutant fluxes from cities, for comparison with emissions inventories, which are themselves commonly used for prediction of current and future air quality and to help guide abatement strategies. Fluxes of NOx were measured using the eddy-covariance technique from an aircraft flying at low altitude over London. The highest fluxes were observed over central London, with lower fluxes measured in suburban areas. A footprint model was used to estimate the spatial area from which the measured emissions occurred. This allowed comparison of the flux measurements to the UK's National Atmospheric Emissions Inventory (NAEI) for NOx, with scaling factors used to account for the actual time of day, day of week and month of year of the measurement. The comparison suggests significant underestimation of NOx emissions in London by the NAEI, mainly due to its under-representation of real world road traffic emissions. A comparison was also carried out with an enhanced version of the inventory using real world driving emission factors and road measurement data taken from the London Atmospheric Emissions Inventory (LAEI). The measurement to inventory agreement was substantially improved using the enhanced version, showing the importance of fully accounting for road traffic, which is the dominant NOx emission source in London. In central London there was still an underestimation by the inventory of 30–40% compared with flux measurements, suggesting significant improvements are still required in the NOx emissions inventory.

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VOC emission rates over London and South East England obtained by airborne eddy covariance

Faraday Discussions ◽

10.1039/c7fd00002b ◽

2017 ◽

Vol 200 ◽

pp. 599-620 ◽

Cited By ~ 10

Author(s):

Adam R. Vaughan ◽

James D. Lee ◽

Marvin D. Shaw ◽

Pawel K. Misztal ◽

Stefan Metzger ◽

...

Keyword(s):

Eddy Covariance ◽

Ground Surface ◽

Monitoring And Evaluation ◽

Proton Transfer Reaction ◽

Emission Rates ◽

Eddy Covariance Method ◽

Emissions Inventory ◽

Mixing Ratios ◽

Spatially Resolved ◽

South East England

Volatile organic compounds (VOCs) originate from a variety of sources, and play an intrinsic role in influencing air quality. Some VOCs, including benzene, are carcinogens and so directly affect human health, while others, such as isoprene, are very reactive in the atmosphere and play an important role in the formation of secondary pollutants such as ozone and particles. Here we report spatially-resolved measurements of the surface-to-atmosphere fluxes of VOCs across London and SE England made in 2013 and 2014. High-frequency 3-D wind velocities and VOC volume mixing ratios (made by proton transfer reaction – mass spectrometry) were obtained from a low-flying aircraft and used to calculate fluxes using the technique of eddy covariance. A footprint model was then used to quantify the flux contribution from the ground surface at spatial resolution of 100 m, averaged to 1 km. Measured fluxes of benzene over Greater London showed positive agreement with the UK’s National Atmospheric Emissions Inventory, with the highest fluxes originating from central London. Comparison of MTBE and toluene fluxes suggest that petroleum evaporation is an important emission source of toluene in central London. Outside London, increased isoprene emissions were observed over wooded areas, at rates greater than those predicted by a UK regional application of the European Monitoring and Evaluation Programme model (EMEP4UK). This work demonstrates the applicability of the airborne eddy covariance method to the determination of anthropogenic and biogenic VOC fluxes and the possibility of validating emission inventories through measurements.

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Preserving the variance in imputed eddy-covariance measurements: Alternative methods for defensible gap filling

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2016.10.018 ◽

2017 ◽

Vol 232 ◽

pp. 635-649 ◽

Cited By ~ 3

Author(s):

Sujit Kunwor ◽

Gregory Starr ◽

Henry W. Loescher ◽

Christina L. Staudhammer

Keyword(s):

Eddy Covariance ◽

Alternative Methods ◽

Gap Filling ◽

Eddy Covariance Measurements

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Corrigendum to “Surface energy balance of an extensive green roof as quantified by full year eddy-covariance measurements” [577 (2017) 220–230/article number]

The Science of The Total Environment ◽

10.1016/j.scitotenv.2021.149698 ◽

2022 ◽

Vol 802 ◽

pp. 149698

Author(s):

Jannik Heusinger ◽

Stephan Weber

Keyword(s):

Energy Balance ◽

Surface Energy ◽

Eddy Covariance ◽

Surface Energy Balance ◽

Green Roof ◽

Extensive Green Roof ◽

Eddy Covariance Measurements

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Comparison of three evapotranspiration models with eddy covariance measurements for a Populus euphratica Oliv. forest in an arid region of northwestern China

Journal of Arid Land ◽

10.1007/s40333-015-0017-0 ◽

2015 ◽

Vol 8 (1) ◽

pp. 146-156 ◽

Cited By ~ 6

Author(s):

Guanlong Gao ◽

Xiaoyou Zhang ◽

Tengfei Yu ◽

Bing Liu

Keyword(s):

Eddy Covariance ◽

Arid Region ◽

Populus Euphratica ◽

Northwestern China ◽

Eddy Covariance Measurements ◽

Populus Euphratica Oliv

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Application of an alternative method to derive reliable estimates of nighttime respiration from eddy covariance measurements in moderately complex topography

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2008.01.015 ◽

2008 ◽

Vol 148 (6-7) ◽

pp. 1174-1180 ◽

Cited By ~ 45

Author(s):

Eva van Gorsel ◽

Ray Leuning ◽

Helen A. Cleugh ◽

Heather Keith ◽

Miko U.F. Kirschbaum ◽

...

Keyword(s):

Eddy Covariance ◽

Complex Topography ◽

Alternative Method ◽

Eddy Covariance Measurements

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Multi-year eddy covariance measurements of net ecosystem exchange in tropical dry deciduous forest of India

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2021.108351 ◽

2021 ◽

Vol 301-302 ◽

pp. 108351

Author(s):

Suraj Reddy Rodda ◽

Kiran Chand Thumaty ◽

MSS Praveen ◽

Chandra Shekhar Jha ◽

Vinay Kumar Dadhwal

Keyword(s):

Eddy Covariance ◽

Deciduous Forest ◽

Net Ecosystem Exchange ◽

Dry Deciduous Forest ◽

Eddy Covariance Measurements

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Estimating evaporation with thermal UAV data and two-source energy balance models

Hydrology and Earth System Sciences ◽

10.5194/hess-20-697-2016 ◽

2016 ◽

Vol 20 (2) ◽

pp. 697-713 ◽

Cited By ~ 57

Author(s):

H. Hoffmann ◽

H. Nieto ◽

R. Jensen ◽

R. Guzinski ◽

P. Zarco-Tejada ◽

...

Keyword(s):

Heat Flux ◽

Energy Balance ◽

High Resolution ◽

Eddy Covariance ◽

Land Surface ◽

Weather Conditions ◽

Heat Fluxes ◽

Thermal Camera ◽

Model Input ◽

Eddy Covariance Measurements

Abstract. Estimating evaporation is important when managing water resources and cultivating crops. Evaporation can be estimated using land surface heat flux models and remotely sensed land surface temperatures (LST), which have recently become obtainable in very high resolution using lightweight thermal cameras and Unmanned Aerial Vehicles (UAVs). In this study a thermal camera was mounted on a UAV and applied into the field of heat fluxes and hydrology by concatenating thermal images into mosaics of LST and using these as input for the two-source energy balance (TSEB) modelling scheme. Thermal images are obtained with a fixed-wing UAV overflying a barley field in western Denmark during the growing season of 2014 and a spatial resolution of 0.20 m is obtained in final LST mosaics. Two models are used: the original TSEB model (TSEB-PT) and a dual-temperature-difference (DTD) model. In contrast to the TSEB-PT model, the DTD model accounts for the bias that is likely present in remotely sensed LST. TSEB-PT and DTD have already been well tested, however only during sunny weather conditions and with satellite images serving as thermal input. The aim of this study is to assess whether a lightweight thermal camera mounted on a UAV is able to provide data of sufficient quality to constitute as model input and thus attain accurate and high spatial and temporal resolution surface energy heat fluxes, with special focus on latent heat flux (evaporation). Furthermore, this study evaluates the performance of the TSEB scheme during cloudy and overcast weather conditions, which is feasible due to the low data retrieval altitude (due to low UAV flying altitude) compared to satellite thermal data that are only available during clear-sky conditions. TSEB-PT and DTD fluxes are compared and validated against eddy covariance measurements and the comparison shows that both TSEB-PT and DTD simulations are in good agreement with eddy covariance measurements, with DTD obtaining the best results. The DTD model provides results comparable to studies estimating evaporation with similar experimental setups, but with LST retrieved from satellites instead of a UAV. Further, systematic irrigation patterns on the barley field provide confidence in the veracity of the spatially distributed evaporation revealed by model output maps. Lastly, this study outlines and discusses the thermal UAV image processing that results in mosaics suited for model input. This study shows that the UAV platform and the lightweight thermal camera provide high spatial and temporal resolution data valid for model input and for other potential applications requiring high-resolution and consistent LST.

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