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| Titel |
On the Validation of Air Quality Models in Megacities using Satellite Measurements: A Case Study in the Pearl River Delta |
| VerfasserIn |
Gerrit Kuhlmann, Hung-Ming Cheung, Andreas Hartl, Mark O. Wenig, Yun-Fat Lam |
| 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 |
250087171
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| Publikation (Nr.) |
 EGU/EGU2014-1191.pdf |
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| Zusammenfassung |
| Recently, many efforts have been made to improve satellite measurements of air pollutants
for applications on a regional scale [1-3]. These improved measurements can be used to
validate chemistry transport simulations in megacities. However, special care must be taken
for such validations, because the trace gas retrieval algorithm depends in part on the
chemistry transport simulation itself. In our study, we compared chemistry transport
simulations with nitrogen dioxide (NO2) measurements of the Ozone Monitoring
Instrument (OMI) in the Pearl River Delta (PRD) megacity (South China). Our
objective was to determine the feasibility to validate models using current satellite
products.
The Community Multiscale Air Quality (CMAQ) Modelling System, has been used to
model air pollutants in winter 2006/2007. The model domain encloses the PRD with a
horizontal grid resolution of 3 km. We included an improved vertical advection scheme and
updated emissions using the newest inventory available.
In the OMI NO2 retrieval algorithms [4,5], an air mass factor (AMF) converts slant
column densities (SCD) to vertical column densities (VCD). The AMF describes the
instrument sensitivity and depends on surface reflectance, atmospheric scattering and the
NO2 profile shape. We computed improved AMFs with the radiative transfer model
SCIATRAN using terrain height, NO2 profile shapes and aerosol profiles taken from
CMAQ. These model-dependent parameter are validated with NO2 and aerosol
concentrations of the PRD air quality network. Updated surface reflectances are taken from
MODIS.
The OMI measurements are mapped to the CMAQ grid using a newly developed gridding
algorithm [6]. Finally, the VCDs have been converted to ground concentrations using the
NO2 profile shapes.
In our validation, we removed the dependency of the trace gase retrieval on a chemistry
transport model. As a result, the retrieval uncertainties of the satellite product were reduced
significantly. The approach allows to analyse every model dependency on the AMFs and to
determine its impact on the VCDs. In our final product, the new gridding algorithm results in
smoother distributions and reconstructs extreme values more accurately. The presented
method is suitable to validate local chemistry transport simulations with satellite
measurements.
References:
[1] Zhou et al.: An improved tropospheric NO2 retrieval for OMI observations in the
vicinity of mountainous terrain, Atmos. Meas. Tech., 2009.
[2] Russel et al.: A high spatial resolution retrieval of NO2 column densities from OMI:
method and evaluation, Atmos. Chem. Phys., 2011.
[3] Lin et al.: Retrieving tropospheric nitrogen dioxide over China from the Ozone
Monitoring Instrument: effects of aerosols, surface reflectance anisotropy and vertical profile
of nitrogen dioxide, Atmos. Chem. Phys. Discuss, 2013.
[4] Bucsela et al.: A new stratospheric and tropospheric NO2 retrieval algorithm
for nadir-viewing satellite instruments: applications to OMI, Atmos. Meas. Tech.,
2013.
[5] Boersma et al.: An improved tropospheric NO2 column retrieval algorithm for the
Ozone Monitoring Instrument, Atmos. Meas. Tech., 2011.
[6] Kuhlmann et al.: A novel gridding algorithm to create regional trace gas maps from
satellite observations, Atmos. Meas. Tech., 2013. |
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