title: Marked long-term decline in ambient CO mixing ratio in SE England, 1997-2014: evidence of policy success in improving air quality.
abstract: Atmospheric CO at Egham in SE England has shown a marked and progressive decline since 1997, following adoption of strict controls on emissions. The Egham site is uniquely positioned to allow both assessment and comparison of 'clean Atlantic background' air and CO-enriched air downwind from the London conurbation. The decline is strongest (approximately 50 ppb per year) in the 1997-2003 period but continues post 2003. A 'local CO increment' can be identified as the residual after subtraction of contemporary background Atlantic CO mixing ratios from measured values at Egham. This increment, which is primarily from regional sources (during anticyclonic or northerly winds) or from the European continent (with easterly air mass origins), has significant seasonality, but overall has declined steadily since 1997. On many days of the year CO measured at Egham is now not far above Atlantic background levels measured at Mace Head (Ireland). The results are consistent with MOPITT satellite observations and 'bottom-up' inventory results. Comparison with urban and regional background CO mixing ratios in Hong Kong demonstrates the importance of regional, as opposed to local reduction of CO emission. The Egham record implies that controls on emissions subsequent to legislation have been extremely successful in the UK.
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
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authors.initials: D
authors.lastname: Lowry
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
authors.forename: M E
authors.initials: ME
authors.lastname: Lanoisellé
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
authors.forename: R E
authors.initials: RE
authors.lastname: Fisher
authors.affiliation: Institute of Technology in Architecture, ETH, CH-8093 Hönggerberg, Zürich, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Martin
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.|Darwin College, Cambridge, CB3 9EU, UK.
authors.forename: C M R
authors.initials: CM
authors.lastname: Fowler
authors.affiliation: School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: J L
authors.initials: JL
authors.lastname: France
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.|Escuela de Ingeniería y Ciencias, Tecnologico de Monterrey, Campus Monterrey, Av. Eugenio Garza Sada 2501, Monterrey, N.L., México, 64849.
authors.forename: I Y
authors.initials: IY
authors.lastname: Hernández-Paniagua
authors.affiliation: NOAA/ESRL Global Monitoring Division, 325 Broadway GMD-1, Boulder CO 80303, USA.
authors.forename: P C
authors.initials: PC
authors.lastname: Novelli
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Sriskantharajah
authors.affiliation: Irish Environmental Protection Agency, Richview, Clonskeagh Rd., Dublin 14, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: O'Brien
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
authors.forename: N D
authors.initials: ND
authors.lastname: Rata
authors.affiliation: St. Richard's Church, Forge Lane, Hanworth, Middlesex, TW13 6UN, UK.
authors.forename: C W
authors.initials: CW
authors.lastname: Holmes
authors.affiliation: National Centre for Atmospheric Science (NCAS), Department of Chemistry, University of Leicester, Leicester, LE1 7RH, UK.
authors.forename: Z L
authors.initials: ZL
authors.lastname: Fleming
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
authors.forename: K C
authors.initials: KC
authors.lastname: Clemitshaw
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Zazzeri
authors.affiliation: Sorbonne Universités, UPMC Univ. Paris 06, Université Versailles St-Quentin; UMR8190, CNRS/INSU, LATMOS-IPSL, Paris, France.
authors.forename: M
authors.initials: M
authors.lastname: Pommier
authors.affiliation: Environment and Climate Change Canada, Air Quality Research Division, Toronto, Ontario MTH 5T4, Canada.
authors.forename: C A
authors.initials: CA
authors.lastname: McLinden
authors.affiliation: Dept. of Earth Sciences, Royal Holloway, Univ. of London, Egham, Surrey, TW20 0EX, United Kingdom.
authors.forename: E G
authors.initials: EG
authors.lastname: Nisbet