 |
| Titel |
Isoprene emissions over Asia 1979-2012: impact of climate and land-use changes |
| VerfasserIn |
T. Stavrakou, J.-F. Müller, M. Bauwens, I. De Smedt, M. Van Roozendael, A. Guenther, M. Wild, X. Xia |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 9 ; Nr. 14, no. 9 (2014-05-12), S.4587-4605 |
| Datensatznummer |
250118691
|
| Publikation (Nr.) |
 copernicus.org/acp-14-4587-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
Due to the scarcity of
observational constraints and the rapidly changing environment in East and
Southeast Asia, isoprene emissions predicted by models are expected to bear
substantial uncertainties. The aim of this study is to improve upon the
existing bottom-up estimates, and to investigate the temporal evolution of
the fluxes in Asia over 1979–2012. To this purpose, we calculate the hourly
emissions at 0.5°×0.5° resolution using the
MEGAN–MOHYCAN model driven by ECMWF ERA-Interim climatology. In order to
remedy for known biases identified in previous studies, and to improve the
simulation of interannual variability and trends in emissions, this study
incorporates (i) changes in land use, including the rapid expansion of oil
palms, (ii) meteorological variability according to ERA-Interim, (iii)
long-term changes in solar radiation (dimming/brightening) constrained by
surface network radiation measurements, and (iv) recent experimental evidence
that South Asian tropical forests are much weaker isoprene emitters than
previously assumed, and on the other hand, that oil palms have a strong
isoprene emission capacity. These effects lead to a significant lowering
(factor of 2) in the total isoprene fluxes over the studied domain, and to
emission reductions reaching a factor of 3.5 in Southeast Asia. The bottom-up
annual isoprene emissions for 2005 are estimated at 7.0, 4.8, 8.3, and
2.9 Tg in China, India, Indonesia and Malaysia, respectively. The isoprene
flux anomaly over the whole domain and studied period is found to be strongly
correlated with the Oceanic Niño Index (r = 0.73), with positive
(negative) anomalies related to El Niño (La Niña) years.
Changes in temperature and solar radiation are the major drivers of the
interannual variability and trends in the emissions, except over semi-arid
areas such as northwestern China, Pakistan and Kazakhstan, where soil
moisture is by far the main cause of interannual emission changes. In our
base simulation, annual positive flux trends of 0.2% and 0.52%
throughout the entire period are found in Asia and China, respectively,
related to a positive trend in temperature and solar radiation. The impact of
oil palm expansion in Indonesia and Malaysia is to enhance the trends over
that region, e.g., from 1.17% to 1.5% in 1979–2005 in Malaysia. A
negative emission trend is derived in India (−0.4%), owing to the
negative trend in solar radiation data associated with the strong dimming
effect likely due to increasing aerosol loadings.
The bottom-up emissions are compared to field campaign measurements in Borneo
and South China and further evaluated against top-down isoprene emission
estimates constrained by GOME-2/MetOp-A formaldehyde columns through
2007–2012. The satellite-based estimates appear to support our assumptions,
and confirm the lower emission rate in tropical forests of Indonesia and
Malaysia. Additional flux measurements are clearly needed to characterize the
spatial variability of emission factors better. Finally, a
decreasing trend in the inferred top-down Chinese emissions since 2007 is in
line with recorded cooling in China after that year, thus suggesting that the
satellite HCHO columns are able to capture climate-induced changes in
emissions. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|