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| Titel |
Initial results from a CO2 monitoring network in the Los Angeles megacity |
| VerfasserIn |
S. Newman, Y. K. Hsu, E. A. Kort, S. P. Sander, A. Eldering, R. M. Duren, C. E. Miller, Y. L. Yung |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064816
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| Zusammenfassung |
| Urban regions, such as Los Angeles, CA, contain more than half of the world’s population
and contribute an even larger fraction of its greenhouse gas (GHG) emissions. One
practical method for tracking these emissions is by high-resolution space-borne
remote-sensing instruments, such as the Orbiting Carbon Observatory (OCO-2, spatial
resolution of ~3 km2). In conjunction with space-borne measurements, in situ
measurements can be used to elucidate the details of urban emission patterns and trends.
Indeed, to understand GHG emissions in complex urban regions, we must sample
in multiple locations with the goal of obtaining specific information from each
site.
We have studied CO2 in Los Angeles from three sites that form the anchor points of a
developing megacity monitoring network. The sites form a ~45 km transect that
extends from the Pacific Ocean coastline to the southwest, over the Los Angeles
basin, to the San Gabriel Mountains that form the northern boundary of the basin.
Using in situ measurements of CO2 from Palos Verdes peninsula (PV), Pasadena,
and Mt. Wilson (MW), from May 2010 – April 2011, with additional analysis of
data since 2001 in Pasadena, we determined the seasonal variations of boundary
layer CO2 mixing ratios. The amplitude of the seasonal and diurnal variations is
much larger in Pasadena than at the other two sites, and the PV site shows more
variability than the MW site. PV is on the coast, with dominant westerly breezes
bringing air from the ocean, except when unusual weather patterns occur. The average
patterns here reflect the global clean-air pattern, with lowest mixing ratios during
the summer and highest during the winter. Pasadena is inland, in the San Gabriel
Valley close to the mountains, and is a good receptor site for receiving the emissions
signal from the Los Angeles basin. The CO2 signal here is strongly affected by
diurnal changes in boundary layer height, reflected in diurnal variations averaging 70
ppm during winter, with the lowest mixing ratios during mid-day. Mt. Wilson is
at 1.7 km elevation in the San Gabriel Mountains, and is above the mixed layer
for much of the time, except during mid-day when the boundary layer frequently
expands above its location and when upslope flow brings a small signal from the
basin, resulting in a peak in mid-afternoon. Our calculations indicate that, when
space-borne remote-sensing instruments look at these three sites, they will observe the
clean-air signal at both PV and MW, whereas the anthropogenic signal, including its
seasonal cycle, will be clearly seen within the Los Angeles basin at the Pasadena site. |
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