Abstract. A total of 14 chemical transport models (CTMs) participated in
the first topic of the Model Inter-Comparison Study for Asia (MICS-Asia)
phase III. These model results are compared with each other and an extensive
set of measurements, aiming to evaluate the current CTMs' ability in
simulating aerosol concentrations, to document the similarities and
differences among model performance, and to reveal the characteristics of
aerosol components in large cities over East Asia. In general, these CTMs
can well reproduce the spatial–temporal distributions of aerosols in East
Asia during the year 2010. The multi-model ensemble mean (MMEM) shows
better performance than most single-model predictions, with correlation
coefficients (between MMEM and measurements) ranging from 0.65 (nitrate,
NO3-) to 0.83 (PM2.5). The
concentrations of black carbon (BC), sulfate
(SO42-), and PM10 are
underestimated by MMEM, with normalized mean biases (NMBs) of −17.0 %,
−19.1 %, and −32.6 %, respectively. Positive biases are simulated
for NO3- (NMB = 4.9 %), ammonium
(NH4+) (NMB = 14.0 %), and PM2.5
(NMB = 4.4 %). In comparison with the statistics calculated from
MICS-Asia phase II, frequent updates of chemical mechanisms in CTMs during
recent years make the intermodel variability of simulated aerosol
concentrations smaller, and better performance can be found in reproducing
the temporal variations of observations. However, a large variation (about a
factor of 2) in the ratios of SNA (sulfate, nitrate, and ammonium) to
PM2.5 is calculated among participant models. A more intense secondary
formation of SO42- is simulated by Community Multi-scale Air Quality (CMAQ)
models, because of the higher SOR (sulfur oxidation ratio) than other
models (0.51 versus 0.39). The NOR (nitric oxidation ratio) calculated by all
CTMs has larger values (∼0.20) than the observations,
indicating that overmuch NO3- is
simulated by current models. NH3-limited condition (the mole ratio of
ammonium to sulfate and nitrate is smaller than 1) can be successfully
reproduced by all participant models, which indicates that a small reduction
in ammonia may improve the air quality. A large coefficient of variation
(CV > 1.0) is calculated for simulated coarse particles,
especially over arid and semi-arid regions, which means that current CTMs
have difficulty producing similar dust emissions by using different dust
schemes. According to the simulation results of MMEM in six large Asian
cities, different air-pollution control plans should be taken due to
their different major air pollutants in different seasons. The MICS-Asia
project gives an opportunity to discuss the similarities and differences of
simulation results among CTMs in East Asian applications. In order to acquire
a better understanding of aerosol properties and their impacts, more
experiments should be designed to reduce the diversities among air quality
models.
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