Evaluation the effects of BC/OC based on the updated emissions inventory in northern China
BC/OC is receiving increasing attention from both the scientific community and the public in China, as the rapidly developing areas in northern China have observed visible air pollution. Providing accurate present-day modelled atmospheric composition of BC/OC, as well as possible future developments, to society and policymakers is critical. A key step towards this is to use up-to-date emission inventories and carefully evaluated models.
Based on the up-to-date emission inventory, the CRAES-CMAQ model simulates air pollutant concentrations (BC,OC,O3,SO2, NO2, PM2.5, PM10 and CO, etc.) in the Chinese region from January 1, 2018 to December 31, 2018. The monthly average BC/OC concentration in key cities in northern China showed (Fig.1) that the simulation results with the up-to-date emission inventory could well simulate the BC/OC concentration in northern China, and the overestimation of the baseline emission inventory and the simulated pollutant concentration could be significantly improved. The simulated BC/OC concentration showed a trend of high in autumn and winter and low in spring and summer. Figure 2 shows the spatial distribution of the simulated annual mean values of BC and OC during 2018. The simulated spatial distribution trend of BC/OC shows that the concentration of BC/OC is higher in Beijing-Tianjin-Hebei and its surrounding areas, the three eastern provinces and some cities in the northwest. The regional distribution of BC/OC concentration in Beijing-Tianjin-Hebei region is more extensive. The average annual concentration of BC was less than 25μg/m3 and that of OC was less than 45μg/m3.
Figure 1 - Simulated monthly mean concentration of BC/OC in key cities of northern China
Figure 2 - The spatial distribution of simulated annual BC/OC concentration
Atmospheric concentrations of air pollutants are also simulated with the global chemical-transport model OsloCTM3 using the new Chinese emissions provided within the project. Results are evaluated against measurements and compared with corresponding output using the most recent global emission inventory, the Community Emission Data System 2021 release (CEDSv21). For the simulations, we replace CEDSv21 emissions with the new inventory in China, keeping the former for the rest of the world. Figure 3 shows the resulting annual mean burden of BC, primary organic aerosol (POA), sulfate, and nitrate aerosols using the new emissions (top) and the ratio between the new inventory and CEDSv21 (bottom).
As shown by the top panels, the air pollution levels are higher in the more densely populated eastern China region, whereas lower pollution levels are seen further west, in agreement with the emission patterns. We note that while local emissions dominate the pollution levels, some pollution is also transported in over China from neighbouring regions such as India in these global simulations. For China as a whole, emissions from the new inventory are lower than in CEDSv21 for all provided species except OC, ranging from 9% lower for total annual BC emissions to 43% lower for SO2 emissions. This result in lower regionally averaged atmospheric burdens for BC, sulfate, and nitrate but higher burden of organic aerosols, compared to model simulations using CEDSv21. Underlying these regional means are regional differences. For instance, while the sulfate burden is consistently lower across China with the new emissions, by up to 20-30% in some areas, BC and POA burdens are higher in the northeast and northwest by up to 60-70%, but lower to the southeast. Hence, both absolute magnitudes and spatial distribution of emissions contribute to the differences between inventories, sometimes in opposing directions.
Figure 3 - (top) Annual mean atmospheric burden of BC, primary organic aerosol (POA), sulfate, and nitrate aerosol simulated with the OsloCTM3 with new year 2018 Chinese emissions and CEDSv21 emissions for the rest of the world and (bottom) Ratio of burdens simulated with the new emissions and with CEDSv21 Chinese emissions.