Surface ozone and its precursors at Summit, Greenland: comparison between observations and model simulations
Recent studies have shown significant challenges for atmospheric models to simulate tropospheric ozone (O<sub>3</sub>) and its precursors in the Arctic. In this study, ground-based data were combined with a global 3-D chemical transport model (GEOS-Chem) to examine the abundance and s...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-12-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/14661/2017/acp-17-14661-2017.pdf |
| Summary: | Recent studies have shown significant challenges for atmospheric
models to simulate tropospheric ozone (O<sub>3</sub>) and its precursors in the
Arctic. In this study, ground-based data were combined with a global 3-D
chemical transport model (GEOS-Chem) to examine the abundance and seasonal
variations of O<sub>3</sub> and its precursors at Summit, Greenland
(72.34° N, 38.29° W; 3212 m a.s.l.). Model simulations for
atmospheric nitrogen oxides (NO<sub><i>x</i></sub>), peroxyacetyl nitrate (PAN), ethane
(C<sub>2</sub>H<sub>6</sub>), propane (C<sub>3</sub>H<sub>8</sub>), carbon monoxide (CO), and O<sub>3</sub>
for the period July 2008–June 2010 were compared with observations. The model
performed well in simulating certain species (such as CO and C<sub>3</sub>H<sub>8</sub>),
but some significant discrepancies were identified for other species and
further investigated. The model generally underestimated NO<sub><i>x</i></sub> and PAN (by ∼ 50 and 30 %, respectively) for March–June. Likely
contributing factors to the low bias include missing NO<sub><i>x</i></sub> and PAN
emissions from snowpack chemistry in the model. At the same time, the model
overestimated NO<sub><i>x</i></sub> mixing ratios by more than a factor of 2 in
wintertime, with episodic NO<sub><i>x</i></sub> mixing ratios up to 15 times higher than
the typical NO<sub><i>x</i></sub> levels at Summit. Further investigation showed that
these simulated episodic NO<sub><i>x</i></sub> spikes were always associated with
transport events from Europe, but the exact cause remained unclear. The model
systematically overestimated C<sub>2</sub>H<sub>6</sub> mixing ratios by approximately
20 % relative to observations. This discrepancy can be resolved by
decreasing anthropogenic C<sub>2</sub>H<sub>6</sub> emissions over Asia and the US by ∼ 20 %, from 5.4 to 4.4 Tg year<sup>−1</sup>. GEOS-Chem was able to reproduce the
seasonal variability of O<sub>3</sub> and its spring maximum. However, compared
with observations, it underestimated surface O<sub>3</sub> by approximately 13 %
(6.5 ppbv) from April to July. This low bias appeared to be driven by several
factors including missing snowpack emissions of NO<sub><i>x</i></sub> and nitrous acid in
the model, the weak simulated stratosphere-to-troposphere exchange flux of
O<sub>3</sub> over the summit, and the coarse model resolution. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |