Marc D. Coleman

Airborne and satellite remote sensing of the mid-infrared water vapour continuum.

Remote sensing of the atmosphere from space plays an increasingly important role in weather forecasting. Exploiting observations from the latest generation of weather satellites relies on an accurate knowledge of fundamental spectroscopy, including the water vapour continuum absorption. Field campaigns involving the Facility for Airborne Atmospheric Measurements research aircraft have collected a comprehensive dataset, comprising remotely sensed infrared radiance observations collocated with accurate measurements of the temperature and humidity structure of the atmosphere. These field measurements have been used to validate the strength of the infrared water vapour continuum in comparison with the latest laboratory measurements. The recent substantial changes to self-continuum coefficients in the widely used MT_CKD (Mlawer–Tobin–Clough–Kneizys–Davies) model between 2400 and 3200 cm−1 are shown to be appropriate and in agreement with field measurements. Results for the foreign continuum in the 1300–2000 cm−1 band suggest a weak temperature dependence that is not currently included in atmospheric models. A one-dimensional variational retrieval experiment is performed that shows a small positive benefit from using new laboratory-derived continuum coefficients for humidity retrievals.

Absolute high spectral resolution measurements of surface solar radiation for detection of water vapour continuum absorption

Solar-pointing Fourier transform infrared (FTIR) spectroscopy offers the capability to measure both the fine scale and broadband spectral structure of atmospheric transmission simultaneously across wide spectral regions. It is therefore suited to the study of both water vapour monomer and continuum absorption behaviours. However, in order to properly address this issue, it is necessary to radiatively calibrate the FTIR instrument response. A solar-pointing high-resolution FTIR spectrometer was deployed as part of the ‘Continuum Absorption by Visible and Infrared radiation and its Atmospheric Relevance’ (CAVIAR) consortium project. This paper describes the radiative calibration process using an ultra-high-temperature blackbody and the consideration of the related influence factors. The result is a radiatively calibrated measurement of the solar irradiation at the ground across the IR region from 2000 to 10 000 cm−1 with an uncertainty of between 3.3 and 5.9 per cent. This measurement is shown to be in good general agreement with a radiative-transfer model. The results from the CAVIAR field measurements are being used in ongoing studies of atmospheric absorbers, in particular the water vapour continuum.

State of UK emissions monitoring of stacks and flues: an evaluation of proficiency testing data for SO2, NO and particulates

We report an examination of the UK stack testing industry’s proficiency for monitoring industrial emissions of SO2, NO and particulates from 2000 to 2011. Data were taken from three proficiency testing schemes run by the National Physical Laboratory (NPL), UK; Calibration Gas Scheme (gas bottle certified reference materials), Gas Measurement Scheme (using a Stack Simulator Facility to test the entire measurement system) and Particulate Scheme (foil shims and salt solutions—i.e., filter and probe washing simulants). In each round of each scheme, participants’ deviations from assigned value were normalised to an allowable deviation based on the required uncertainty for stack emission measurements stipulated in the European Union’s Industrial Emissions Directive. This normalisation produced a z-score and limits were set to define satisfactory, warning and unsatisfactory participant performance. As a function of time, it was found that across all schemes, the number of unsatisfactory/outlier scores decreased, evidencing an overall improvement in industry proficiency. With regard to the gas schemes, it was found that the industry had a poorer proficiency for SO2 than NO and that there was a distribution bias toward negative scores in the Gas Measurement scheme consistent with SO2 sample losses in drying units. It was evident that this industry bias was insufficient to force the vast majority of the industry outside of the satisfactory z-score limits; however, it was noted that this issue should be carefully monitored in the future.

Mass emissions and carbon trading: a critical review of available reference methods for industrial stack flow measurement

Flow measurements in industrial ducts and stacks are combined with pollutant or greenhouse gas concentrations to deduce mass emissions. These are then used to populate pollutant emission inventories and are traded under emissions trading schemes. Reference methods for flow are described in ISO 10780 and more recently in EN ISO 16911-1. This paper discusses the key differences between the two standards. We consider sources of error in flow measurement and discuss how each standard addresses them. We find that EN ISO 16911-1 introduces a series of improvements that when combined provide critical uncertainty gains that support compliance with the EU’s Emissions Trading System (EU ETS). All these areas are either not addressed or only partially dealt with in ISO 10780. More specifically, EN ISO 16911-1, (a) specifies a wider range of reference techniques enabling the optimal one to be used for different flue gas environments. (b) Provides a method to correct for cyclonic flow effects. (c) Addresses measurement assembly misalignment and specifies tolerance values for it and (d) provides wall effect correction factors. Most importantly, it has been validated through laboratory and field work. However, the quality control specified in EN ISO 16911-1 is more suitable for measurements to support EU ETS requirements and at times can be too onerous for pollutant mass emission reporting that will usually have less stringent uncertainty requirements.

Testing equivalency of an alternative method based on portable FTIR to the European Standard Reference Methods for monitoring emissions to air of CO, NOx, SO2, HCl, and H2O

We compare the performance of an alternative method based on portable Fourier-transform infrared (FTIR) spectroscopy described in TGN M22, “Measuring Stack Gas Emissions Using FTIR Instruments,” to the Standard Reference Methods (SRMs) for CO (EN 15058), NOx (EN 14792), SO2 (EN 14791), HCl (EN 1911), and H2O (EN 14790). Testing was carried out using a Stack Simulator facility generating complex gas matrices of the measurands across concentration ranges of 0–75 mg m−3 and 0–100 mg m−3 CO, 0–200 mg m−3 and 0–300 mg m−3 NO, 0–75 mg m−3 and 0–200 mg m−3 SO2, 0–15 mg m−3 and 0–60 mg m−3 HCl, and 0–14 vol% H2O. The former values are the required monitoring range for each measurand as described in the European Union (EU) Industrial Emissions Directive (2010/75/EU) for waste incineration processes, and the latter are supplementary ranges representative of emissions from some large combustion plant processes. Test data were treated in accordance with CEN/TS 14793, and it was found that equivalency test criteria could be met across all concentration ranges with the exception of the NO supplementary range. The results demonstrated in principle where TGN M22/FTIR could be used in place of the existing SRMs to provide, as required under the Industrial Emissions Directive, annual validation/calibration of automated measuring systems (AMSs being permanently installed on industrial stacks to provide continuous monitoring of emissions to air). These data take a step toward the wider regulatory acceptance of portable FTIR providing the advantages of real-time calibration and quantification of all measurands on a single technique. Implications: Portable FTIR offers significant advantages for the calibration (as is required by the EU’s Industrial Emissions Directive, 2010/75/EU) of process plant operators instrumentation installed for continuous monitoring of emissions to air. All key gaseous emission species regulated under the directive can be calibrated using a single technique, and the real-time calibration data allows issues with plant instrumentation to be identified sooner, reducing the amount of time where unreliable emissions data might be reported from the plant. This work takes an important step toward the regulatory acceptance of portable FTIR for the validation/calibration of in situ emissions monitoring systems.

Flow rate measurement in stacks with cyclonic flow – Error estimations using CFD modelling

Abstract Two methods of flow measurement in stacks are investigated to determine their errors in presence of cyclonic flow. One method – based on velocity measurements with a Pitot tube in a grid of points – is the standard reference method according to EN ISO 16911-1. The second method – ultrasonic flow measurement – is often used as the automated measurement system in stacks according to EN ISO 16911-2. Several typical stack configurations are considered and the flow field in the stacks is obtained using validated computational fluid dynamics (CFD) modelling with OpenFoam software. We show that possible errors of the standard reference method due to the cyclonic flow are significant compared to the requirements of the EU’s Emissions Trading System. For the ultrasonic flow meter we compare various configurations (number, orientation, position) of the ultrasound beams and we demonstrate the flow profile pre-investigation by CFD as prescribed in section 8.3 of EN ISO 16911-2.