Regional CO pollution in China simulated by the high-resolution nested-grid GEOS-Chem model

Abstract:

An updated version of the nested-grid GEOSChem
model is developed allowing for higher horizontal
(0.5×0.667) resolution as compared to global models. CO
transport over a heavily polluted region, the Beijing-Tianjin-
Hebei (BTH) city cluster in China, and the pattern of outflow
from East China in summertime are investigated. Comparison
of the nested-grid with global models indicates that the
fine-resolution nested-grid model is capable of resolving individual
cities with high associated emission intensities. The
nested-grid model indicates the presence of a high CO column
density over the Sichuan Basin in summer, attributable
to the low-level stationary vortex associated with the Basin’s
topographical features. The nested-grid model provides good
agreement also with measurements from a suburban monitoring
site in Beijing during summer 2005. Tagged CO simulation
results suggest that regional emissions make significant
contributions to elevated CO levels over Beijing on polluted
days and that the southeastward moving cyclones bringing
northwest winds to Beijing are the key meteorological mechanisms
responsible for dispersion of pollution over Beijing in
summer. Overall CO fluxes to the NW Pacific from Asia are
found to decrease by a factor of 3–4 from spring to summer.
Much of the seasonal change is driven by decreasing
fluxes from India and Southeast Asia in summer, while
fluxes from East China are only 30% lower in summer than in
spring. Compared to spring, summertime outflow from Chinese
source regions is strongest at higher latitudes (north of
35 N). The deeper convection in summer transporting CO
to higher altitudes where export is more efficient is largely
responsible for enhanced export in summer.

Notes:

Final Manuscript in DASH