Tall tower measurements of methane, carbon monoxide and carbon dioxide emissions in London, UK

Helfter, Carole; Tremper, Anja; Nemitz, Eiko; Barlow, Janet F.. 2014 Tall tower measurements of methane, carbon monoxide and carbon dioxide emissions in London, UK. [Speech] In: InGOS 2nd Periodic Project Meeting, Florence, Italy, 14-16 Oct 2014. (Unpublished)

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London, with a population of 8.2 million, is the largest city in Europe. It is heavily built-up (typically 8% vegetation cover within the central boroughs) and boasts some of the busiest arteries in Europe despite efforts to reduce traffic in the city centre with the introduction of a congestion charging scheme in 2007. We report on over two years of continuous measurements atop a tall tower in the heart of London between October 2011 and present. Fluxes of methane (CH4), carbon monoxide (CO) and carbon dioxide (CO2) are measured by eddy-covariance from the top of the British Telecom (BT) tower in central London (51° 31’ 17.4” N, 0° 8’ 20.04” W). The eddy-covariance system consists of a Gill R3-50 ultrasonic anemometer located 192 m above street level , a Picarro G2301-f cavity ring-down spectrometer for the measurement of CH4, CO2 and water, and an Aero-Laser AL5002 carbon monoxide analyser. Air is sampled 0.3 m below the sensor head of the ultrasonic anemometer and pulled down 45 m of 12.7 mm OD Teflon tubing. CO2 emissions were found to be mainly controlled by fossil fuel combustion (e.g. traffic, commercial and domestic heating) and diurnal averages of CO2 fluxes are highly correlated to traffic. However changes in heating-related natural gas consumption and, to a lesser extent, photosynthetic activity in two large city centre green spaces (Hyde Park and Regent’s Park) explained the seasonal variability. Annual estimates of net exchange of CO2 (41 ktons m-2) obtained by eddy-covariance agreed well with up-scaled data from the UK National Atmospheric Emissions Inventory (NAEI). CO fluxes were correlated to both CO2 and CH4; the estimated net emissions of CO for 2013 were 156 ± 40 tons km-2 which is in reasonable agreement with the 2012 London Atmospheric Emissions Inventory (LAEI) value of 90 tons km-2 and with independent measurement-based estimates which report a range of 105 to 220 tons km-2 (Harrison et al., 2012; O’Shea et al., 2014). Methane emissions from central London exhibit diurnal trends both for concentrations and fluxes. Fluxes are strongly correlated to those of carbon dioxide and although flux ratios exhibit diurnal cycles they are relatively constant on an annual basis. The baseline for methane fluxes is thought to result from leaks in the natural gas distribution network at a rate of 30 tons km-2 yr-1. However, a two- to three-fold difference was found between inventory and measured total fluxes, which could indicate an underestimation of CH4 emissions from combustion sources by the inventory (e.g. road traffic, domestic and commercial heating). Central London methane emissions are estimated at 70 tons km-2 yr-1 and the global warming effect of CO2 was found to be 25 times greater than that of CH4 (100-year horizon). References: Harrison et al., 2012, Atmospheric Chemistry and Physics, 12(6), 3065-3114. O’Shea et al., 2014, Journal of Geophysical Research: Atmospheres, 119(8), 4940–4952.

Item Type: Publication - Conference Item (Speech)
UKCEH and CEH Sections/Science Areas: Dise
NORA Subject Terms: Atmospheric Sciences
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Date made live: 13 Nov 2014 16:25 +0 (UTC)

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