Abstract
Long-range pollution transport (LRT) events have a wide impact across East Asia, but are often difficult to track due to imprecise emission inventories and changing domain scales as the plume moves from source to receptor locations. This study adjusts a bottom-up emission inventory based on changes in remotely sensed NO2 column densities for a source region of East Asia, then with CMAQv5.2.1 simulates transport of LRT plumes to Taiwan. Adjustment of an emissions inventory based on satellite measurements during the COVID-19 lockdown in China led to a ~59% reduction in emissions over the relevant source area in China compared to base emissions. As a result, PM2.5 mass concentrations were reproduced to match observations (mean fractional bias, MFB of -13.9% and 18.5% at a remote and urban station) as the plume passed through northern Taiwan. Furthermore, the OMI-adjusted emissions simulation brought all of the major PM2.5 components to within ~50% of the measured values. Another LRT event from 2018 with more subtle OMI-adjustments to the emissions was also simulated and with improved overall PM2.5 mass concentration at the northern tip of Taiwan (MFB: -91.5%) compared to the base model (MFB: -102.1%), and an acceptable index of agreement (0.78). For the 2018 event, non sea-salt sulfate concentrations were consistently underpredicted (0.2–0.4), while nitrate concentrations were overpredicted by up to factor of 11. Copernicus Atmosphere Monitoring Service (CAMS) reanalysis of the PM2.5 concentrations shows high sulfate concentrations in eastern China in the areas associated with 72-h back-trajectories from northern Taiwan during both events, lending support for future model investigations of sulfate source area production and transport to Taiwan. In order to better track these LRT events out of East Asia and optimize OMI-adjustment methodology, it is recommended to explore other satellite-based products to map unaccounted for SO2 sources upstream of Taiwan.
Highlights
For more than a decade, there have been frequent haze incidents in eastern China during winter and spring, generating and exporting excessive amounts of PM2.5, particulate matter smaller than 2.5 microns in diameter (Fu et al, 2014; Yang et al, 2016)
Long-range pollution transport (LRT) events have a wide impact across East Asia, but are often difficult to track due to imprecise emission inventories and changing domain scales as the plume moves from source to receptor locations
OMI-adjustment of the emissions inventory during the 2020 long-range transport event at the beginning of the COVID-19 lockdown in China led to ~59% lower NOx emissions than the base emissions scenario, in the area associated with the event backtrajectories (Griffith et al, 2020)
Summary
For more than a decade, there have been frequent haze incidents in eastern China during winter and spring, generating and exporting excessive amounts of PM2.5, particulate matter smaller than 2.5 microns in diameter (Fu et al, 2014; Yang et al, 2016). Aerosol and Air Quality Research | https://aaqr.org et al, 2008; Zhang et al, 2015; Wang et al, 2016; Chuang et al, 2017; Hsu and Cheng, 2019). During these long-range transport (LRT) events, the northern and western parts of Taiwan, accounting for 95% of its population, are primarily impacted by this transported PM2.5, posing an excess health risk to the island’s residents (Song et al, 2011; Loftus et al, 2015; Griffith et al, 2020). All of the aforementioned studies were focused on improving the simulation of monthly to annual averages
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