A study of uncertainties in the sulfate distribution and its radiative forcing associated with sulfur chemistry in a global aerosol model 1Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan
03 Nov 2011
2Research Institute for Applied Mechanics, Kyusyu University, Kasuga, Fukuoka, Japan
3Graduate School of Environmental Studies, Nagoya University, Nagoya, Aichi, Japan
Received: 23 December 2010 – Published in Atmos. Chem. Phys. Discuss.: 19 April 2011 Abstract. The direct radiative forcing by sulfate aerosols is still uncertain, mainly
because the uncertainties are largely derived from differences in sulfate
column burdens and its vertical distributions among global aerosol models.
One possible reason for the large difference in the computed values is that
the radiative forcing delicately depends on various simplifications of the
sulfur processes made in the models. In this study, therefore, we
investigated impacts of different parts of the sulfur chemistry module in a
global aerosol model, SPRINTARS, on the sulfate distribution and its
radiative forcing. Important studies were effects of simplified and more
physical-based sulfur processes in terms of treatment of sulfur chemistry,
oxidant chemistry, and dry deposition process of sulfur components. The
results showed that the difference in the aqueous-phase sulfur chemistry
among these treatments has the largest impact on the sulfate distribution.
Introduction of all the improvements mentioned above brought the model
values noticeably closer to in-situ measurements than those in the
simplified methods used in the original SPRINTARS model. At the same time,
these improvements also brought the computed sulfate column burdens and its
vertical distributions into good agreement with other AEROCOM model values.
The global annual mean radiative forcing due to the direct effect of
anthropogenic sulfate aerosol was thus estimated to be −0.26 W m−2
(−0.30 W m−2 with a different SO2 inventory), whereas the original
SPRINTARS model showed −0.18 W m−2 (−0.21 W m−2 with a different
SO2 inventory). The magnitude of the difference between original and
improved methods was approximately 50% of the uncertainty among estimates
by the world's global aerosol models reported by the IPCC-AR4 assessment
report. Findings in the present study, therefore, may suggest that the model
differences in the simplifications of the sulfur processes are still a part
of the large uncertainty in their simulated radiative forcings.
Revised: 09 October 2011 – Accepted: 24 October 2011 – Published: 03 November 2011
Citation: Goto, D., Nakajima, T., Takemura, T., and Sudo, K.: A study of uncertainties in the sulfate distribution and its radiative forcing associated with sulfur chemistry in a global aerosol model, Atmos. Chem. Phys., 11, 10889-10910, doi:10.5194/acp-11-10889-2011, 2011.