Interannual variation, decadal trend, and future change in ozone outflow from East Asia
We examine the past and future changes in the O<sub>3</sub> outflow from East Asia using a global 3-D chemical transport model, GEOS-Chem. The simulations of Asian O<sub>3</sub> outflow for 1986–2006 are driven by the assimilated GEOS-4 meteorological fields, and those for 20...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/3729/2017/acp-17-3729-2017.pdf |
| Summary: | We examine the past and future changes in the O<sub>3</sub> outflow from
East Asia using a global 3-D chemical transport model,
GEOS-Chem. The simulations of Asian O<sub>3</sub> outflow for 1986–2006 are
driven by the assimilated GEOS-4 meteorological fields, and those for
2000–2050 are driven by the meteorological fields archived by the NASA Goddard
Institute for Space Studies (GISS) general circulation model (GCM) 3 under
the IPCC SRES A1B scenario. The evaluation of the model results against
measurements shows that the GEOS-Chem model captures the
seasonal cycles and interannual variations of tropospheric O<sub>3</sub>
concentrations fairly well with high correlation coefficients of 0.82–0.93 at four
ground-based sites and 0.55–0.88 at two ozonesonde sites where
observations are available. The increasing trends in surface-layer O<sub>3</sub>
concentrations in East Asia over the past 2 decades are captured by the
model, although the modeled O<sub>3</sub> trends have low biases. Sensitivity
studies are conducted to examine the respective impacts of meteorological
parameters and emissions on the variations in the outflow flux of O<sub>3</sub>.
When both meteorological parameters and anthropogenic emissions varied
from 1986–2006, the simulated Asian O<sub>3</sub> outflow fluxes exhibited a
statistically insignificant decadal trend; however, they showed large interannual variations
(IAVs) with seasonal values of 4–9 % for the absolute percent departure from the mean (APDM)
and an annual APDM value of 3.3 %. The sensitivity simulations
indicated that the large IAVs in O<sub>3</sub> outflow fluxes were mainly caused
by variations in the meteorological conditions. The variations in meteorological
parameters drove the IAVs in O<sub>3</sub> outflow fluxes by altering the O<sub>3</sub>
concentrations over East Asia and by altering the zonal winds; the latter
was identified to be the key factor, since the O<sub>3</sub> outflow was highly
correlated with zonal winds from 1986–2006. The simulations of the
2000–2050 changes show that the annual outflow flux of O<sub>3</sub> will
increase by 2.0, 7.9, and 12.2 % owing to
climate change alone, emissions change alone, and changes in both climate
and emissions, respectively. Therefore, climate change will aggravate the effects of the
increases in anthropogenic emissions on future changes in the Asian O<sub>3</sub>
outflow. Future climate change is predicted to greatly increase the Asian
O<sub>3</sub> outflow in the spring and summer seasons as a result of the
projected increases in zonal winds. The findings from the present study help us to
understand the variations in tropospheric O<sub>3</sub> in the downwind regions of
East Asia on different timescales and have important implications for
long-term air quality planning in the regions downwind of China, such as
Japan and the US. |
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| ISSN: | 1680-7316 1680-7324 |