image: The proportion of combustion-related isoprene emission to the total from both biogenic and combustion sources in February of 2000 (a) and 2016 (b).
Credit: ©Science China Press
This study is led by Dr. Guofeng Shen (Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University) and Prof. Xinming Wang (State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences). The role of isoprene, a highly reactive organic gas, as a precursor for secondary organic aerosols (SOA) has been well-established. However, compared to biogenic sources, isoprene emissions from incomplete fuel combustions and their contribution to SOA formation remain poorly understood, with data and knowledge gaps related to emissions, transport, and contributions to SOA formation. In most simulations, the modelled SOA levels are significantly lower than observed values, with the lack of non-biogenic isoprene emissions being a key factor leading to this discrepancy.
The research team from Peking University and Guangzhou Institute of Geochemistry, CAS developed a new isoprene emission inventory that includes both biogenic and combustion sources. This bottom-up inventory was established by compiling available emission factor data for various sources and fuel consumption data from the GEMS database (formerly known as PKU-fuel, https://gems.pku.edu.cn). The new inventory was subsequently incorporated into CMAQ model simulations to quantitatively analyze the seasonal and annual variations of isoprene-derived SOA.
The study found that combustion-related isoprene emissions from outdoor biomass burning and residential fuel use were estimated at approximately 52.0 Gg in 2000, decreasing to 14.8 Gg in 2016, primarily due to the transition from solid fuels to cleaner energy sources. “This again highlights the significant environmental and health benefits of the energy transition, as reducing reactive organic gases like isoprene contributes to improved air quality, particularly in underdeveloped regions where solid fuels are still widely used,” says Guofeng Shen. While annual emissions of combustion-related isoprene are much lower than those from biogenic sources, in cold winters, they can account for 32-80% of total isoprene emissions in northern and western provinces of China (see image NO.1).
Previous studies often found that winter SOA values simulated by atmospheric models were lower than observed values. By incorporating the new inventory that includes combustion-related sources, this study demonstrated significant improvements in simulation accuracy, with the discrepancy between model outputs and observed values reduced to within a factor of 2, compared to previous discrepancies up to 66 (see image NO.2). Model simulations suggest that combustion-related isoprene may contribute 25-40% of winter SOA in northern regions.
In winter, when emissions from fuel combustions¾especially for space heating in north and western regions¾are higher, combustion-related isoprene can account for up to 40% of the total SOA. This highlights the importance of incorporating combustion sources into isoprene emission inventories and their contribution to ambient aerosols. Future research could expand from regional to global scales, with more accurate and reliable data supporting effective air quality management strategies.
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See the article:
Combustion-related isoprene contributes substantially to the formation of wintertime secondary organic aerosols
https://doi.org/10.1093/nsr/nwae474
Journal
National Science Review