High-resolution modeling of the distribution of surface air pollutants and their intercontinental transport by a global tropospheric atmospheric chemistry source–receptor model (GNAQPMS-SM)
Authors: Ye Qian , Li Jie , Chen Xueshun , Chen Huansheng , Yang Wenyi , Du Huiyun , Pan Xiaole , Tang Xiao , Wang Wei , Zhu Lili , Li Jianjun , Wang Zhe , Wang Zifa 
Published: December 2021

Abstract. Many efforts have been devoted to quantifying the impact
of intercontinental transport on global air quality by using global chemical
transport models with horizontal resolutions of hundreds of kilometers in
recent decades. In this study, a global online air quality source–receptor
model (GNAQPMS-SM) is designed to effectively compute the contributions of
various regions to ambient pollutant concentrations. The newly developed
model is able to quantify source–receptor (S-R) relationships in one
simulation without introducing errors by nonlinear chemistry. We calculate
the surface and planetary boundary layer (PBL) S-R relationships in 19
regions over the whole globe for ozone (O3), black carbon (BC), and
non-sea-salt sulfate (nss-sulfate) by conducting a high-resolution
(0.5∘ × 0.5∘) simulation for the year 2018.
The model exhibits a realistic capacity in reproducing the spatial
distributions and seasonal variations of tropospheric O3, carbon
monoxide, and aerosols at global and regional scales – Europe (EUR), North
America (NAM), and East Asia (EA). The correlation coefficient (R) and
normalized mean bias (NMB) for seasonal O3 at global background and
urban–rural sites ranged from 0.49 to 0.87 and −2 % to 14.97 %,
respectively. For aerosols, the R and NMB in EUR, NAM, and EA mostly exceed
0.6 and are within ±15 %. These statistical parameters based on this
global simulation can match those of regional models in key regions. The
simulated tropospheric nitrogen dioxide and aerosol optical depths are
generally in agreement with satellite observations. The model overestimates
ozone concentrations in the upper troposphere and stratosphere in the
tropics, midlatitude, and polar regions of the Southern Hemisphere due to
the use of a simplified stratospheric ozone scheme and/or biases in
estimated stratosphere–troposphere exchange dynamics. We find that surface
O3 can travel a long distance and contributes a non-negligible fraction
to downwind regions. Non-local source transport explains approximately
35 %–60 % of surface O3 in EA, South Asia (SAS), EUR, and NAM. The
O3 exported from EUR can also be transported across the Arctic Ocean to
the North Pacific and contributes nearly 5 %–7.5 % to the North Pacific. BC
is directly linked to local emissions, and each BC source region mainly
contributes to itself and surrounding regions. For nss-sulfate,
contributions of long-range transport account for 15 %–30 % within the PBL
in EA, SAS, EUR, and NAM. Our estimated international transport of BC and
nss-sulfate is lower than that from the Hemispheric Transport of Air
Pollution (HTAP) assessment report in 2010, but most surface O3 results
are within the range. This difference may be related to the different
simulation years, emission inventories, vertical and horizontal resolutions,
and S-R revealing methods. Additional emission sensitivity simulation shows
a negative O3 response in receptor region EA in January from EA. The
difference between two methods in estimated S-R relationships of
nss-sulfate and O3 are mainly due to ignoring the nonlinearity of
pollutants during chemical processes. The S-R relationship of aerosols
within EA subcontinent is also assessed. The model that we developed creates
a link between the scientific community and policymakers. Finally, the
results are discussed in the context of future model development and
analysis opportunities.