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| Titel |
Airborne Flux Measurements of Volatile Organic Compounds and NOx over a European megacity |
| VerfasserIn |
Marvin Shaw, James Lee, Brian Davison, Pawel Misztal, Thomas Karl, Nick Hewitt, Alistair Lewis |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089280
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| Publikation (Nr.) |
 EGU/EGU2014-3477.pdf |
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| Zusammenfassung |
| Ground level ozone (O3) and nitrogen dioxide (NO2) are priority pollutants whose
concentrations are closely regulated by European Union Air Quality Directive 2008/50/EC.
O3 is a secondary pollutant, produced from a complex chemical interplay between oxides of
nitrogen (NOx = NO + NO2) and volatile organic compounds (VOCs). Whilst the basic
atmospheric chemistry leading to O3 formation is generally well understood, there
are substantial uncertainties associated with the magnitude of emissions of both
VOCs and NOx. At present our knowledge of O3 precursor emissions in the UK is
primarily derived from National Atmospheric Emission inventories (NAEI) that provide
spatially disaggregated estimates at 1x1km resolution, and these are not routinely
tested at city or regional scales. Uncertainties in emissions propagate through into
uncertainties in predictions of air quality in the future, and hence the likely effectiveness of
control policies on both background and peak O3 and NO2 concentrations in the
UK.
The Ozone Precursor Fluxes in the Urban Environment (OPFUE) project aims to quantify
emission rates for NOx and selected VOCs in and around the megacity of London using
airborne eddy covariance (AEC). The mathematical foundation for AEC has been extensively
reviewed and AEC measurements of ozone, dimethyl sulphide, CO2 and VOCs have been
previously reported.
During the summer of 2013, approximately 30 hours of airborne flux measurements of
toluene, benzene, NO and NO2 were obtained from the NERC Airborne Research and Survey
Facility’s (ARSF) Dornier-228 aircraft. Over SE England, flights involved repeated south
west to north east transects of ~50 km each over Greater London and it’s surrounding
suburbs and rural areas, flying at the aircraft’s minimum operating flight altitude and airspeed
(~300m, 80m/s). Mixing ratios of benzene and toluene were acquired at 2Hz using
a proton transfer reaction mass spectrometer (PTR-MS) and compared to twice
hourly whole air canister samples (WAS) which were quantitatively determined
post-flight via TD-GCMS. Mixing ratios between the PTR-MS and WAS-TD-GCMS
were in good agreement with R2 values of 0.8 and 1.0 for Toluene and Benzene
respectively. Mixing ratios of NO and NO2 were acquired at 10Hz using a 2 channel NOx
chemiluminescence detector with photolytic converter. These measurements were
used with 20 Hz 3-D wind vector data from an AIMMS-20 turbulence probe on
the aircraft to calculate highly spatially resolved (1 km) surface-to-atmosphere
emission flux rates of these compounds using the eddy covariance method of Karl et al.
(2013).
Measured surface to atmosphere emission fluxes of NOx, benzene and toluene from London
were between 40 – 91 mg m2 h-1, 0.1 – 0.4 mg m2 h-1 and 0.2 – 2 mg m2 h-1 respectively,
showing the spatial flux heterogeneity over the city.
This demonstrates for the first time the feasibility of airborne eddy covariance flux
measurements of reactive NOx species. We also show the applicability of wavelet analysis
using virtually disjunct eddy covariance measurements of anthropogenic compounds in
estimating regional fluxes over a European megacity. We compare our measured emission
rates with those estimated from “bottom-up” emissions inventories and highlight the
agreement between the two. |
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