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Journal article

Nested-grid simulation of mercury over North America

Zhang Y, Jaegl?? L, Van Donkelaar A, Martin R, Holmes C, Amos H, Wang Q, Talbot R, Artz R, Brooks S, Luke W, Holsen T, Felton D, Miller E, Perry K, Schmeltz D, Steffen A, Tordon R, Weiss-Penzias P, Zsolway R ...see all

Atmospheric Chemistry and Physics, vol. 12, issue 14 (2012) pp. 6095-6111

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Abstract

We have developed a new nested-grid mercury (Hg) simulation over North
America with a 1/2A degrees latitude by 2/3A degrees longitude
horizontal resolution employing the GEOS-Chem global chemical transport
model. Emissions, chemistry, deposition, and meteorology are
self-consistent between the global and nested domains. Compared to the
global model (4A degrees latitude by 5A degrees longitude), the nested
model shows improved skill at capturing the high spatial and temporal
variability of Hg wet deposition over North America observed by the
Mercury Deposition Network (MDN) in 2008-2009. The nested simulation
resolves features such as higher deposition due to orographic
precipitation, land/ocean contrast and and predicts more efficient
convective rain scavenging of Hg over the southeast United States.
However, the nested model overestimates Hg wet deposition over the Ohio
River Valley region (ORV) by 27%. We modify anthropogenic emission
speciation profiles in the US EPA National Emission Inventory (NEI) to
account for the rapid in-plume reduction of reactive to elemental Hg
(IPR simulation). This leads to a decrease in the model bias to -2.3%
over the ORV region. Over the contiguous US, the correlation coefficient
(r) between MDN observations and our IPR simulation increases from 0.60
to 0.78. The IPR nested simulation generally reproduces the seasonal
cycle in surface concentrations of speciated Hg from the Atmospheric
Mercury Network (AMNet) and Canadian Atmospheric Mercury Network
(CAMNet). In the IPR simulation, annual mean gaseous and
particulate-bound Hg(II) are within 140% and 11% of observations,
respectively. In contrast, the simulation with unmodified anthropogenic
Hg speciation profiles overestimates these observations by factors of 4
and 2 for gaseous and particulate-bound Hg(II), respectively. The nested
model shows improved skill at capturing the horizontal variability of Hg
observed over California during the ARCTAS aircraft campaign. The nested
model suggests that North American anthropogenic emissions account for
10-22% of Hg wet deposition flux over the US, depending on the
anthropogenic emissions speciation profile assumed. The modeled percent
contribution can be as high as 60% near large point sources in ORV. Our
results indicate that the North American anthropogenic contribution to
dry deposition is 13-20%.

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