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| Titel |
Aircraft observations of the urban CO2 dome in London and calculated daytime CO2 fluxes at the urban-regional scale |
| VerfasserIn |
Anna Font, Josep Anton Morguí, Sue Grimmond, Benjamin Barratt |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082479
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| Zusammenfassung |
| Traffic, industry and energy production and consumption within urban boundaries emit great
amounts of CO2 into the atmosphere, creating an urban increment of CO2 mixing ratios
compared to the surrounding rural atmosphere. Monitoring CO2 within these ‘urban domes’
has been proposed as a means to evaluate the effectiveness of policies aiming to mitigate and
reduce CO2 urban emissions (CMEGGE, 2010).
London is the biggest urban conurbation in Western Europe with more than 8 million
inhabitants, and it emitted roughly 45000 ktn CO2 in 2010 (DECC, 2012). In order
to develop and implement observational strategies to measure the contribution of
urban areas into the global carbon cycle, two airborne surveys were deployed using
the Natural and Environment Research Council - Airborne Research and Survey
Facility (NERC-ARSF). High frequency measurements of atmospheric CO2, O3,
particles and meteorological variables were taken over London in October 2011 and
July 2012. CO2 mixing ratios were measured by a Non-Dispersive IR instrument
developed by AOS. In July 2012, a Cavity Ring-Down Spectroscopy (CDRS) instrument
developed by PICARRO was deployed measuring CO2, CH4 and water vapour at
1Hz resolution. The objectives of the campaigns were to measure the CO2 dome
over London and to calculate CO2 emissions at the urban-regional-scale. London
was crossed by two transects (SW-NE and SSE-NNW) at an altitude of 360 m and
vertical profiles up to 2000 m were carried out to characterize the structure of the
atmosphere.
Aircraft measurements allowed observation on how CO2 domes were shaped by
meteorological conditions. In October 2011, the mean CO2 mixing ratio measured in London
was on average 2 ppmv higher than the suburban measurements within the boundary layer.
However, under low wind speeds, the CO2 mixing ratio in the urban mixing ratio
peaked in central London (>10 ppmv) and decreased towards the city boundaries.
Under windy conditions, the structure of the urban dome was dispersed downwind,
with peak concentrations displaced from the urban centre along the main wind
direction.
The urban-regional surface CO2 flux was calculated for four days in October 2011 by
either the Integrative Mass Boundary Layer (IMBL) or the Column Integration
method (CIM), dependent on meteorological conditions. The diurnal CO2 flux in
London obtained from the aircraft observations ranged from 36 to 71 μmol CO2
m-2 s-1 during the day time. This compared well with continuous measurements
of CO2 exchange by an eddy-covariance system located in central London. The
day-to-day variability observed in the calculated CO2 fluxes responded to the spatial
variability of the influence area and emissions that observations were sensitive
to.
This study provides an example how aircraft surveys in urban areas can be used to
estimate CO2 surface fluxes at the urban-regional scale. It also presents an important
cross-validation of two independent measurement-based methods to infer the contribution of
urban areas to climate change in terms of CO2 emissions that complement bottom-up
emissions inventories.
References
Committee on Methods for Estimating Greenhouse Gas Emissions (2010), The National
Academia Press.
DECC (2012), http://www.decc.gov.uk/en/content/cms/statistics/indicators/ni186/ni186.aspx |
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