DEVELOPMENT AND APPLICATION OF DISJUNCT EDDY COVARIANCE TECHNIQUES FOR THE MEASUREMENT AND INTERPRETATION OF FLUXES OF VOLATILE ORGANIC COMPOUNDS FROM URBAN AND RURAL CANOPIES Ben Langford BSc. (Hons.) A thesis submitted for the degree of Doctor of Philosophy, Lancaster University. Faculty of Science Environmental Science Department Lancaster University May 2008 ProQuest Number: 11003731 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 11003731 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ii Abstract Acknowledgements I offer my sincere gratitude to my supervisors here at Lancaster University, Professor Nick Hewitt and Dr Brian Davison without whose support, guidance and patience none of this work would have been possible. I would also like to pay special tribute to Dr Eiko Nemitz (CEH, Edinburgh), not only for his supervision, but for sharing his knowledge and enthusiasm for the subject and for offering up his valuable time to answer my many questions. I offer my gratitude to Dr Malcolm Possell and Dr Mick Wilkinson for their continued support and advice, as well as to Annette Ryan and Jullada Laothawornkitkul who provided a welcome distraction whenever needed. I also thank my colleagues at CEH Edinburgh, Dr Gavin Phillips, Dr Daniela Famulari, Dr Claire Campbell, Pawel Misztal and Emily House without whose sense of fun, the days spent in the field would have felt much longer. I would like to acknowledge the technical skills of both Geoff Johnson and Ian Edmondson which were invaluable to this project. I am indebted to the Natural Environmental Research Council for financing this studentship and supplying funds for conferences and research meetings. Finally, for her patience, support, understanding and brew making skills, I owe my partner, Jen, a huge debt of gratitude. Development and application of disjunct eddy covariance techniques for the measurement and interpretation of fluxes of volatile organic compound from urban and rural canopies Ben Langford BSc. (Hons.) This thesis is submitted for the degree of Doctor of Philosophy and is the work of the above author. It has not been submitted for a higher degree elsewhere. May 2008 Abstract Two disjunct eddy covariance systems for the measurement of volatile organic compound (VOC) fluxes were developed. The first, disjunct eddy covariance (DEC), was validated against the standard eddy covariance (EC) technique, in a study of CO 2 and EbO fluxes from a grassland field (Easter Bush, Edinburgh, Scotland). The comparison convincingly showed fluxes measured by the DEC technique to be comparable to those measured using the EC technique. A second, simplified approach, virtual disjunct eddy covariance (vDEC), was developed and compared against standard DEC during the CityFlux project, where measurements of VOC fluxes were made from Portland Tower in Manchester. Averaged daily fluxes measured by the vDEC system typically ranged between 19 and 90 pg m'2 h'1 for individual VOC species and were comparable to those measured by the DEC system, but were typically 19% higher than the latter. The discrepancies between the two methods were thought to relate to both the reduced response time of the DEC system which attenuated higher frequency flux contributions iv Abstract and the high level of noise in the covariance function which may have led to a systematic overestimation of the flux. The vDEC technique was subsequently deployed on the Telecom Tower in central London to give very detailed flux information on seven VOC species. Individual average fluxes ranged between 5 and 100 jug m'2 h'1 and were well correlated with traffic density. Fluxes of benzene were extrapolated to give an annual emission estimate for the city, which was found to be 1.8 times lower than that suggested by the National Atmospheric Emission Inventory. Finally, two vDEC systems, one using a high sensitivity (HS) proton transfer reaction mass spectrometer (PTR-MS) and the other a standard model (Std), were used alongside each other to measure biogenic VOC fluxes from macchia vegetation at the Castelporziano nature reserve near Rome, Italy. The two systems compared well, although the HS system appeared to give fluxes with greater amplitude than the Std model. This highlighted the importance of the allocation of correct lag times when using vDEC, particularly at night. Fluxes of isoprene and monoterpenes were compared with the Guenther algorithm of 1995 and showed excellent agreement between the modelled and measured values. The results presented in this study have convincingly demonstrated the capacity of the DEC and vDEC techniques to give very detailed VOC flux information over a range of non-ideal canopies, which can be used to both validate and constrain “bottom-up” style emission inventories. Table of contents v Table of Contents Acknowledgements ..................................................................................... ii A b s t r a c t.................................................................................................................. iii Table of contents......................................................................................... v List of figures................................................................................................... x List of tables......................................................................................................vi Nomenclature ...................................................................................................xiii Chapter I i. Introduction....................................................................................l 1.1 Biosphere /Atmosphere interactions........................................1 1.2 Bottom up approach to quantifying trace gas exchange.. 4 1.3 Top up approach to quantifying trace gas exchange..........7 1.4 Atmospheric transport processes............................................. 8 1.5 The conservation equation...................................................... 9 1.6 Enclosure techniques (non aerodynamic technique) .......... 11 1.7 Micrometeorological approaches (aerodynamic)................ 13 1.8 Eddy Covariance........................................................................... 16 1.8.1 Theoretical requirements ................................................................18 1.8.2 Coordinate rotation .........................................................................18 1.8.3 Sensor requirements........................................................................19 1.9 Eddy Accumulation...................................................................... 21 1.10 Relaxed Eddy Accumulation..................................................... 22 1.11 Disjunct Eddy Covariance ..........................................................24 1.12 Aims and objectives......................................................................27 Chapter II II. Methods......................................................................................... 29 2.1 The proton transfer reaction — mass spectrometer.............29 2.1.1 Mass detection................................................................................. 32 2.1.2 Instrument background..................................................................33 2.1.3 The PTR-MS control software ...................................................... 37 2.1.4 Maintaining optimum SEM operating voltage .......................... 39 2.2 Disjunct eddy covariance - concept and design...................40 2.2.1 Theoretical testing of DEC concept ............................................. 41 2.3 The disjunct flux sampler........................................................... 46 2.4 Laboratory testing...................................................................... 47 2.4.1 Effects of changing drift tube pressure ....................................... 49 Table of contents 2.4.2 Correction for sample carryover ..................................................51 2.5 Field testing - evaluation against EC...................................... 52 2.5.1 Field experiment and setup............................................................53 2.5.2 Disjunct flux sampler - setup ..................................................... 54 2.5.3 Eddy covariance - setup .............................................................. 56 2.5.4 Results and discussion................................................................. 56 2.5.5 Concentrations .................................................................................56 2.5.6 Comparison of sensible heat fluxes ..............................................57 2.5.7 Comparison of CO 2 & H 2 O fluxes ................................................60 2.5.8 Potential experiment improvements............................................ 61 2.5.9 Conclusions.......................................................................................62 2.6 Virtual disjunct eddy covariance (vDEC) .......................... 63 2.7