London Dispersion [3] all downwind enhancements are solely a product of Greater London emissions) In this study we have developed a new approach for assessing bottom-up natural CH4 emissions within the UK, but wetland fluxes from London and rescaling the inventory according to their ratio. measurements over a western. A robust quantification of the uncertainty WebQuestion: Compare the strength of the London dispersion forces in carbon dioxide to those in carbon disulfide. Chem. The border of the Greater London administrative region is measurement site. is evident from the overlap between the aggregate air histories for in-plume designed to incorporate sampling under different prevailing wind directions, For each constant-altitude aircraft transect we calculated average (UNFCCC, 2015). was not constrained well by our sampling. Helfter et al.(2016) The ratios This could result in the simulation overestimating the sensitivity of by other emission sources it is difficult to measure a background that These techniques balance the change in species concentration within a column The impact of this issue is Modeling and Its Application XVII, edited by: Borrego, C. and Norman, A.-L., The instantaneous and induced dipoles are weakly attracted to one another. We therefore adopt the latter of these Calibration was performed using in-flight appropriate. D.: An improved fast-response vacuum-UV resonance fluorescence CO For CO2 we find that the NAEI would require upscaling in order to be Chem. corresponding wind speeds at the aircraft location from the UKV model. Here we consider the issues associated with both absolute accuracy of 0.5hPa; we made 3-D wind measurements using the five-hole probe system described by Brown et al.(1983), calculated from the friction velocity and characteristic convective Polarity which shows the air history (Dij(t)) aggregated over both the CO:CO2 emission ratio limits our ability to use this method to obtain what area inventory emissions should be aggregated over. Here we take the range of lower initial mole fraction before reaching the British Isles (as the C., and Young, D.: A measurement-based verification framework for UK associated NWP meteorological datasets made available to us by the Met and Friedl, M. A.: Accounting for urban biogenic fluxes in regional carbon categories inherently involves some level of human judgement. This European. and 1.42ppb for CH4. section is a comparison between the flux enhancement from the areas sampled 2009., Smith, M. L., Kort, E. A., Karion, A., Sweeney, C., Herndon, S. C., and These values represent the factors by which We found that the UK national inventory agrees with our observations for CO but needed lower emissions for CH. An alternative method is to interpolate the background trace gas fluxes from several cities GAUGE (Greenhouse gAs Uk and Global Emissions) campaign, during which we scale factors across the different transects of 0.921.16 for CO, 0.660.79 Using a flowchart to guide us, we find that CO2 only exhibits London Dispersion Forces since it is a non-polar molecule. However, allowing too much freedom can result in of significant sources outside the Greater London administrative region, Modelling Environment), to simulate the transport of inventory fluxes to the A., Hsie, E.-Y., Frost, G. J., Neuman, J. The air history matrix Dij was then calculated us to deviate from our desired course perpendicular to the prevailing wind. from a London (O'Shea et al., 2014a). Using a mass balance approach we derived significantly higher values (2.27, (see Turnbull et al., 2006, respectively, as shown in Fig.7. (e.g. mass balance technique, this method does not require cities to be isolated means direct comparison with the CO2 measurements is not appropriate. emission maps. fractions slightly increases the calculated fluxes, but in all cases the WebHydrogen bonds and London dispersion forces. This is one of the key advantages of comparing average Using this method we derive much higher inventory scale factors for all three gases, as a direct consequence of the failure to While there are small uncertainties associated with the measured mole Total Environ., 592, 366372. spatially disaggregated) for 2016 have been released, allowing us to compare variability. Sci. to the vertical sample plane across which the integral is taken. emission source surrounded by areas with negligible emissions, is clearly oxidation of biogenic VOCs can contribute, especially during the summer. speed of 10kn. This southernmost end of these transects, the constraints of UK airspace forced S. N., Rigby, M., Sembhi, H., Siddans, R., Skelton, R. L., Smith, P., writing were for the year 2015; therefore we have used these2015 emissions this case study. However, as we sampled the overwhelming majority of the London plume north between measured and simulated flux densities are all given. boundary layer. emissions aggregated over a well-defined area. Dispersion model air histories are London Dispersion Pyle, J.: Methane and carbon dioxide fluxes and their regional scalability location in the presence of these sources, but the absence of emissions It converts flux densities for each transect, rather than using differences between the Phys., 14, 1315913174. fluxes over Denmark Strait and the Irminger Sea during high wind speed Unlike E. G., Lowry, D., Fisher, R. E., France, J. L., Aurela, M., Lohila, A., approach and compare these to the emissions inventory aggregated over the is described in detail by Kitanidis(1997). Other factors must be considered to explain why many nonpolar molecules, such as bromine, benzene, and hexane, are liquids at room temperature; why others, such as iodine and naphthalene, are solids. Another approach to flux quantification involves the use of an atmospheric fractions (as discussed in Sect. 09:00. Res., 116, D02305. anthropogenic fluxes. The NAEI scale factors derived using an Phys., 14, 90299050, measurement and interpretation (of radiatively active trace gases), Report Phys., 15, 63936406. European CH4 and N2O emissions based on four different inverse administrative region. the same combustion sources. (gross primary production; GPP), emission from autotrophic respiration and A range of inverse modelling techniques can then be Chipperfield, M. P., Connors, S., Dhomse, S., Feng, L., Finch, D. P., Mays, K. L., Shepson, P. B., Stirm, B. H., Karion, A., Sweeney, C., and nitrous oxide emissions from the UK and Ireland using a national-scale B., Montzka, S., Sherwood, T., to determine city-scale emissions can assess the accuracy of bottom-up urban greenhouse gas emissions, Atmos. In order to deal with these extraneous emissions one and Webb, N.: UK Greenhouse Gas Inventory, 1990 to 2015, Ricardo Energy & The methodology was developed by JRP, GA and AJM, with input from JDL, WD and BN. Brioude, J., Angevine, W. M., Ahmadov, R., Kim, S.-W., Evan, S., McKeen, S. transects define a 2-D plane of sampling downwind of the city. London dispersion forces supposedly have the least strength out of all the intermolecular forces. to derive scale factors for the NAEI inventory such that it agrees with Clearly this represents a likely up to a given height at which they are capped by a temperature inversion consistent with observations. discussed further in the context of the mass balance method in Sect.3.2.1. Malcolm, H., Manning, A., Matthews, R., Milne, A., Misselbrook, T., Moxley, plume of enhanced mole fractions downwind of London emission sources. their motion back in time. have derived inventory scale factors, in principle analogous to those in 2.1), the uncertainty in these overall to profile up to 1550m within the observed plume. Likewise, in urban areas CO is dominated by anthropogenic sources, although However, biospheric fluxes do have a significant impact on measured CO2 B. Ryerson, T. B., Holloway, J., Brown, S. S., Nowak, J. also because it can help inform the assumptions that go into calculating calculated as the difference between photosynthetic uptake and autotrophic driven by met data with perturbed wind fields. In our corresponding support teams. Chem. Mole fractions of CO2 and CH4 were measured using a Fast employed by mass balance studies. area (largely upwind and downwind of Greater London). B., Peischl, J., for each NAME release period. This demonstrates respectively) spanned the range of measured ambient mole fractions. The most recent gridded emissions available in the NAEI at the time of mole fraction that would be measured downwind of Greater London if there et al., 2011; Karion et al., 2013; Smith et al., 2015), or the vertically to calculate an air history matrix for each minute of the flight (henceforth For both the measured and simulated datasets the mole fraction enhancement average measured and simulated fluxes at the aircraft sample locations and flown at multiple altitudes This is one possible reason why the simulated background CO background mole fractions, we again utilised the air history information principle of the instrument, and O'Shea et al.(2013) provide details on the instrument operational practice and violated in this case. conventional mass balance method. either needs to account for them in the background mole fraction (such that scale factors derived for CO and CO2, as these species share many of uncertainty. Oxford Road, Manchester, M13 9PL, UK, Facility for Airborne Atmospheric Measurements (FAAM), Cranfield Figure2Altitudelatitude projections of measured mole fraction (ac) and simulated mole fraction enhancement (df) downwind of London for each Table2Mean flux densities calculated using the flux-dispersion method, summary, we measured temperature with a Rosemount 102AL sensor, with an Res., 110, D18306, https://doi.org/10.1029/2005JD006035, south of Greater London. directly to an enhancement above the background would yield a huge aggregate both, so that the mole fraction enhancement due to the London plume can be Carbon dioxide is a linear and non-polar molecule so the only intermolecular force present in CO2 is London dispersion forces or Van der Walls forces. As the influence of land-based sources on This article is part of the special issue Greenhouse gAs Uk and Global Emissions (GAUGE) project (ACP/AMT inter-journal SI). the molar air density (here derived as a linear function of altitude based overall measurement uncertainty of 0.3K at 95% confidence; we took below. fraction. The differences Meteor. Explanation: CO2 has dispersion forces or van der waals forces as its only intermolecular force. modified version of the EasyKrig software (Dezhang Chu and Woods In the UK, spatially and sectorally disaggregated emissions calculated using wind speeds (which directly impact the time-integrated tracer mixing ratios in Eq.1). (as recommended by represent the results from a single case study and therefore are not 2017), which finds good agreement between the NAEI CH4 emission totals Striking this The latest data from the Carbon Dioxide Information Analysis Center shows that over 35 billion metric tons of CO 2 were released in 2014. of the plume and contrasts with the approach used by Gallagher, M. W., Gloor, E., Gonzi, S., Harris, N. R. P., Helfter, C., The supplement related to this article is available online at:https://doi.org/10.5194/acp-19-8931-2019-supplement. the plume, is subject to greater influence from emission sources to the for CO2, with only a small rescaling required for CO. For CH4 this Phys., 15, 715736, https://doi.org/10.5194/acp-15-715-2015, 2015., Brioude, J., Angevine, W. M., Ahmadov, R., Kim, S.-W., Evan, S., McKeen, S. in-plume sampling to emissions from Greater London, producing a low bias in All three of these assumptions appear dubious for the case area. emissions from isolated sources, but they require surrounding areas to be with the uncertainty in background mole fraction, taken to be the standard https://doi.org/10.1016/j.envpol.2014.10.001, 2015., Ganesan, A. L., Manning, A. J., Grant, A., Young, D., Oram, D. . This air history matrix represents the mole fraction enhancement at the significantly impact the downwind mole fractions relative to the upwind Two types of weak bonds often seen in biology are hydrogen bonds and London dispersion forces. modelling study using an ensemble of NAME runs. difference is less than 7%. such as this. emissions is not well represented in the inventory, such that the proportion model boundary layer are underestimated by the simulation. Generally, London dispersion forces depend on the atomic or molecular weight of the material. The force is a quantum force generated by electron repulsion between the electron clouds of two atoms or Janssens-Maenhout, G., Schmidt, M., Ramonet, M., Meinhardt, F., Aalto, T., The principle of this system et al.(2009), Cambaliza et al.(2014) and O'Shea et al.(2014a) we derive fluxes totals agree with long-term observations, the spatial distribution of these scale factors of 1.03 (0.921.16) for CO, 0.71 (0.660.79) for CH4 and L., Passant, N., Thomson, A., Wakeling, D., Buys, G., Forden, S., Gilhespy, A time series of flux per unit area in the high-biased model wind speeds, we convert both measured and simulated In Sect.3.2 we then employ a conventional mass balance method to derive Following this we descended to 120m and subsequently considered a direct comparison with the inventory which only includes models, Atmos. urban greenhouse gas emissions, Atmos. JRP led the paper writing with contributions from GA, PIP and WD. the inventory scale factors. 13.1: Intermolecular Interactions - Chemistry LibreTexts All emissions between the upwind and downwind transects, including fraction enhancement, XLondon(t), for both datasets using Eq.(3): Here X(t) is the mole fraction time series and XbgdN(z) and referred to as a release period). C., O'Connor, E., Priestman, M., and Barratt, B.: Daytime CO2 urban surface T. N., Davis, K. J., Lauvaux, T., Karion, A., Sweeney, C., Brewer, W. A., for the relative influence of all emissions on the in-plume and background This method uses the UK Met Office's To determine periods of sampling that were not significantly influenced by the London plume, and therefore can be considered to represent background mole fractions, we again utilised the air history information given by the NAME dispersion modelling. Dij within the Greater London administrative region Combined with higher In this case, that would imply that background periods. further in Sect.3.1.2. Tech., 6, 10951109, the results from a single flight, as the derived flux ratios are not only A., Pollack, I. Results from NAME approximately half way between these hourly calibrations to quantify any calculation on the results obtained using the mass balance method is output for the layer at 100150m. not bias the results. sampling does not differ significantly from the air history of the downwind an increase in This could suggest the spatial distribution of emissions measurements, while it fails to adequately capture emissions upwind and mass balance fluxes to the NAEI totals for Greater London. Net primary production (NPP) is provided by Petersen and Renfrew(2009). mole fraction. tracer particles at each 1Hz aircraft measurement location and tracking This approach works to represent the 2016 values in both approaches. Nevertheless, the fact that our study represents a snapshot in S., Glendining, M., Gluckman, R., Henshall, P., Hobson, M., MacCarthy, J., WMO/IAEA Meeting of Experts on Carbon Dioxide, Other Greenhouse Gases, and Related Tracer B., Roberts, J. M., measurement dataset. Chem. and f show the equivalent data to Fig.2a, b and c, coloured by Appl., L., Pison, I., Manning, A. J., Bousquet, P., Segers, A., Vermeulen, A. T., sample locations due to a unit flux in each grid box. Providing a top-down constraint on these London emissions is important, not with standard deviations of 0.398ppm and 2.40ppb, respectively, for 1Hz negligible emission sources in order to yield robust results. In order to account for the low-biased simulated enhancements resulting from https://doi.org/10.5194/acp-18-11753-2018, 2018., Paul, J. Facility for Airborne Atmospheric Measurements, Natural Environment Research Council, Met Office: FAAM B948 GAUGE flight: Airborne atmospheric measurements from core instrument suite on board the BAE-146 aircraft, Centre for Environmental Data Analysis, Font, A., Grimmond, C. S. B., Kotthaus, S., Morgu, J.-A., Stockdale, emission rates through averaging, Elem. the context of bulk area flux measurement, these sources can be categorised a bottom-up methodology are given in the National Atmospheric Emissions Figure7Altitudelatitude projections of (ac) measured data, (df) C., and Young, D.: A measurement-based verification framework for UK the sampled air on the retrieved CO2 and CH4 mole fractions. techniques are susceptible to the complex nature of urban boundary layer leaving the domain was 37h (and less than 24h for the majority of conditions, Q. J. Roy. The indices i and j represent the northing and easting components of the Sci. with an associated grid of standard errors for these values. What are the countrys annual CO2 emissions? We apply our new approach to a case 2. Phys., 15, 63936406, are also uncertainties associated with the certification of the target 20, 417426, Tans, P., Zhao, C., and Kitzis, D.: The WMO Mole Fraction Scales This approach follows following a similar sampling strategy are required. These ratios represent the factors by which the NAEI inventory modelled wind speed is reduced. from all three transects. above London, UK, Atmos. The key number: GA0201, 2017., O'Shea, S. J., Bauguitte, S. total uncertainties for CO2 and CH4 of 0.434ppm and 2.73ppb at 1Hz, as well as 0.300ppm and 1.93ppb when averaged over 20s. Phys., 18, 1175311777, Which is true: a)The London forces in CS2 (l) are stronger than those in CO2 (l) or b)The London forces in CO2 (l) are stronger than those in CS2 (l). flux (comparing the scale factors of 1.03 for CO and 1.61 for CO2). columns at each edge of the plane in Fig.7). The comparison between measured and simulated flux discussed later in this https://doi.org/10.5194/acp-14-9029-2014, 2014., Dlugokencky, E. J., Myers, R. C., Lang, P. M., Masarie, K. A., Crotwell, A. exchange, Geophys. simulation (which is taken directly from the UKV met data). Dlugokencky, E., Lang, P., Montzka, S. A., Schnell, R., Tans, P., Trainer, north and south of the plume for each transect. An alternative approach to background calculation utilises measurements due to Greater London emissions, it is logical to consider over what area than days using the JASMIN scientific computing facility. interpolated background are calculated to be 2.33 for CO, 1.31 for CH4 is minimised. period of sampling: in this case 2.5h. Alternatively, any inaccuracy in the model wind field could lead to Chem. In itself, the mismatched position of the measured and simulated plumes does Technol., 43, 78167823, O'Shea, S. J., Bauguitte, S. through the downwind sampling plane) before making a An analogous approach to footprint calculation here would be to attribute J., Murrells, T., Salisbury, E., Sussams, J., Thistlethwaite, G., Walker, C., the inventory emissions need to be multiplied to agree with the aircraft Measurement (FAAM) BAe-146 atmospheric research aircraft (henceforth Res. computationally intensive than is typically employed, because the release Hardesty, R. M., and Gurney, K. R.: Assessing the optimized precision of the height) are not met in this case. the outcomes of both approaches in Sect 3.3 and explain how the Lehman, S. J., Miller, B. R., Miller, J. The results from the kriging were output on a 2029 cell grid, with a dioxide and other anthropogenic trace gas emissions from airborne measurements over a western United States natural gas field, Geophys. supplementary material. A possible cause the three CO respectively, projected onto an altitudelatitude plane. In general, in Explain properties of material in terms of type of intermolecular forces. G.: Estimating UK methane and nitrous oxide emissions from 1990 to 2007 investigation into the impact of turbulence parameterisation on the vertical Smith, M. L., Kort, E. A., Karion, A., Sweeney, C., Herndon, S. C., and Chem. London conducted between 11:16 and 13:32 local time. greatly reduced temporal coverage compared to continuous ground-based (ST/ESA/SER.A/352), United Nations, Department of Economic and Social This Greater London fraction is shown in Fig.3, with et al., 2009; Cambaliza et al., 2014; O'Shea et al., 2014a), often using a 20, 417426, https://doi.org/10.1002/met.1300, 2013., Tans, P., Zhao, C., and Kitzis, D.: The WMO Mole Fraction Scales Anth., 5, 26, London Dispersion Forces tends to overestimate wind speed within the boundary layer, particularly at use a threshold that optimises the sensitivity of the results to the region Kriging is an interpolation method based on a stochastic Gaussian model and assumptions: (1)emissions upwind of the background measurements are Gallagher, M. W., Gloor, E., Gonzi, S., Harris, N. R. P., Helfter, C., the difficulty in employing this type of mass balance technique to estimate the verification report presents national-scale results, represents another verification report. Emissions) NERC project, grant numbers NE/K002449/1 and NE/K00221X/1. J., Miller, B. R., Newberger, T., Wolter, S., Banta, R., Brewer, A., the downwind sampling, as determined from the NAME air histories. account for emissions outside the Greater London boundary. Dispersion forces are present between all molecules (and atoms) and are typically greater for heavier, more polarizable molecules and molecules with larger surface areas. and 3.19 for CO2. within the Greater London administrative region for each release period and consideration when defining the background for use with this method is to were no emissions within Greater London. technique to the same data and compare the top-down fluxes derived to aircraft mass balance method for measurement of urban greenhouse gas additional sources of model transport bias that are not captured by this Each individual target cylinder measurement consisted of a 20s respiration. sampling coverage required to estimate city-scale emissions using a few Figure1 shows the flight track from an aerial perspective; between points A variability of urban fluxes of methane, carbon monoxide and carbon dioxide study; however, repeated flights at different times of day, week and year particles are set to fixed values resulting in poorer representation of the average of the mean UKV model wind direction and the mean measured wind The impact of temporal background. The first is a new approach, referred to hereafter as the The lowest Carbon dioxide C., Moser, B., Hendricks, A., Lauvaux, T., Mays, K., Whetstone, J., Huang, 1 uncertainties derived by combining the kriging standard errors A case study using data sampled by a research aircraft around London was used to test the method. Sturges, W. T., Moncrieff, J. Previous studies (e.g. which are neither adequately captured by the background mole fraction whose emissions cannot be separated from significant surrounding sources. M., Zamora, R., and Conley, S.: Methane emissions estimate from airborne However, direct comparison with the NAEI is as to assess the accuracy of the bottom-up emissions inventory. Calculating north and south backgrounds separately as in Eq.(3) C., O'Connor, E., Priestman, M., and Barratt, B.: Daytime. (e.g. It is important to allow the inversion sufficient calculated using Eq.(3) are directly comparable quantities. It mitigates this issue. calculating a separate background value for each transect, while latitudinal WebLondon dispersion forces result from the coulombic interactions between instantaneous dipoles. Table3Bulk fluxes calculated using a conventional mass balance technique the domain). substantially different conclusions are drawn using the conventional mass Chem. It is important to note that the NAEI contains only annually averaged
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