Air pollution is a global environmental problem with serious impacts on human health, climate change, and ecological systems. In China, rapid development in the last several decades has led to a drastic increase in coal consumption and the number of vehicles. As a result, air pollution in China is complicated by the coexistence of high concentrations of primary and secondary trace gases and aerosol particles from multiple sources.
Air pollution complex is a term used to characterize the formation mechanisms of air pollution, and was first proposed by Professor Xiaoyan Tang in 1997. A better understanding of these complex mechanisms is critical for meeting the urgent societal need to reduce air pollution in China as quickly as possible. To meet these challenges, the National Natural Science Foundation of China (NSFC) initiated a major research program, entitled "Fundamental Researches on the Formation and Response Mechanism of Air Pollution Complex in China." The program, which ran from 2016 to 2023, funded 76 projects with 250 million RMB in total.
Through the NSFC program's 76 projects, scientists have achieved tremendous advances in air pollution research. To raise awareness of air pollution complex, the journal Advances in Atmospheric Sciences recently published a special issue on the topic. "The research programs funded by the Chinese government at different levels have provided solid scientific support to the air pollution control policies in China, and led to the fastest reduction in air pollution in the history," said Tong Zhu, professor at Peking University, the leading scientist of the NSFC program, and one of the guest editors of the special topic. The issue consists of eight articles highlighting some of the most recent research advances related to air pollution complex.
"Air pollution and climate change are closed linked. They are caused by the change of atmospheric components, and interact with each other with the change of radiation, planetary boundary layer height, atmospheric circulation, and cloud formation. Coordinated efforts should be made to reduce air pollution, mitigate climate change, and maximize the health benefits of these efforts," said Zhu. "The scientific knowledge, methods, tools, and data obtained by Chinese scientists about air pollution and science-based control polices need to be shared with global community, especially with Global South countries suffering from severe air pollution."
The articles, contributed by scientists from Chinese universities and research institutions, feature different aspects of air pollution complex research, ranging from instrument development to modeling studies:
" Development and Application of Cavity-based Absorption Spectroscopy in Atmospheric Chemistry: Recent Progress ," by Weixiong Zhao and coauthors, is a review focused on instrument development. The review covers cavity-based absorption spectroscopy techniques and their applications in atmospheric chemistry. Cavity-based absorption spectroscopy uses a high-fineness cavity to achieve a very long absorption path-length and ultra-high sensitivity. This paper helps promote communication in the fields of laser spectroscopy and atmospheric chemistry. The authors overview recent key advances in cavity-based absorption spectroscopy, review their application in trace gases detection, and outline future directions for instrument development.
" The Influence of Heterogeneous Processes on the Physicochemical Properties of Atmospheric Aerosols ," written by Maofa Ge and coauthors, reviews recent advances related to the impact of heterogeneous processes on haze chemistry, including the impact on NO2 chemistry, marine aerosols, and the physiochemical properties of atmospheric aerosols. Heterogeneous reactions play a critical role in the formation of air pollution complexes in China. The paper focuses on new insights from the past five years and proposes future research directions.
" Highly Oxidized Molecules Make a Significant Contribution to Enhanced Aromatic-Derived Secondary Organic Aerosol under a Humid Environment " examines the role relative humidity plays in aromatic secondary organic aerosol formation. Enhanced mass concentrations of aromatic-derived secondary organic aerosol are frequently observed during humid-haze events. However, scientists have not fully understood the influencing mechanism of relative humidity in these events till now. This paper by Zhaomin Yang and coauthors is helpful for a better understanding of humid-haze events.
" Compositions and distributions of secondary organic aerosols and their tracers over the Pearl River Estuary region influenced by continental and marine air masses ," written by Zhenhao Ling and coauthors, explores secondary organic aerosol tracers in the Pearl River Estuary in the winter of 2021. Using the tracer-based method and simulations, they estimated the contribution of key volatile organic compounds to secondary organic aerosols. Their findings improve the understanding of the distributions of secondary organic aerosols and their tracers in different air masses at this site, and highlight the fact that the abundance of secondary organic aerosols over the Pearl River Estuary region is mainly related to precursors and already-formed secondary organic aerosols transported from upwind continental areas.
" Elucidating Secondary Organic Aerosol Processes through High-Resolution Aerosol Mass Spectrometry in Beijing " focuses on a new method to investigate secondary organic aerosol formation in Beijing. Written by Weiqi Xu and coauthors, the work focuses on the critical role of photochemical processes in the formation of sulfur-enriched organic aerosols relative to nitrogen-enriched organic aerosols. The authors emphasize the need to integrate these processes into atmospheric models for more accurate predictions of aerosol composition. Their findings are valuable for devising effective pollution mitigation strategies, particularly in regions with high levels of biomass burning and fossil fuel combustion.
" Effectiveness of precursor emission reductions for the control of summertime ozone and PM2.5 in the Beijing–Tianjin–Hebei Region under different meteorological conditions ." written by Jing Qian and Hong Liao, used ozone and PM2.5 observations, reanalyzed meteorological data, and GEOSChem simulations, to examine the relationships between ozone and PM2.5 concentrations and temperature or relative humidity over Beijing–Tianjin–Hebei in the summer of 2019. They investigated the effectiveness of emissions reduction and discovered that the ozone decrease due to precursor emission reductions was more sensitive to temperature, while the decrease in PM2.5 was more sensitive to relative humidity. As a result, reducing precursor emissions will be more effective in controlling the co-pollution of ozone and PM2.5 during hot and humid conditions. These results are helpful for framing effective policies to reduce ozone and PM2.5 pollution in Beijing–Tianjin–Hebei.
" High-resolution simulation dataset of hourly PM2.5 chemical composition in China (CAQRA-aerosol) from 2013 to 2020 ," written by Lei Kong and coauthors, focused on the development of a PM2.5 chemical composition dataset in China called CAQRA-aerosol. The researchers used the Nested Air Quality Prediction Modeling System with an updated inorganic aerosol module and a new inversed emission inventory. The CAQRA-aerosol dataset includes five aerosol components (organic carbon, black carbon, ammonium, nitrate, and sulfate). It currently provides data from 2013 to 2020, and will be renewed annually. This new dataset achieves much better accuracy than previous datasets. The temporal resolution is also higher than previous datasets, meaning it could provide more detailed information on the concentrations of PM2.5 components.
" A newly established air pollution data center in China ," highlights the China Air Pollution Data Center, the first comprehensive data center on air pollution research in China. Written by Mei Zheng and coauthors, this paper focuses on the Data Center with its 258 datasets and 15 technical reports. This data, classified into eight categories, includes emission inventories, chemical reanalysis, field measurements, satellite observations, laboratory work, source profiles, new technology, and online source appointment technology. The bilingual data platform is accessible in Chinese and English versions.
