“Bottoming” toxic and harmful trace element atmospheric emissions

Whether it is resource utilization or pollution control, understanding the bottom line is a basic and necessary work.

Recently, the team of Professor Tian Hezhong of Beijing Normal University evaluated the driving force of different emission control measures on the atmospheric emissions of toxic and harmful trace elements in various departments during the implementation of the “Ten Atmospheric Rules” (Air Pollution Prevention and Control Action Plan) based on the fusion of multi-source data. The effects of emission changes in typical industries (coal-fired, metallurgy, etc.) on atmospheric exposure concentration and health risks of toxic and harmful trace elements were quantitatively analyzed by using the atmospheric transport model and exposure risk evaluation model. On May 1, the paper was published online in One Earth.

Illustration of atmospheric transport and exposure risks of trace elements. Photo courtesy of interviewee

Trace elements are about health

The International Agency for Research on Cancer (IARC) has identified arsenic, nickel, cadmium, hexavalent chromium, lead, cobalt, antimony and their compounds as carcinogens. These heavy metal elements are very small in the atmosphere, but have the characteristics of toxicity, accumulation and carcinogenicity, and long-term exposure to higher concentrations of harmful trace elements in the atmospheric environment will pose a serious threat to the human respiratory system and cardiovascular system.

In September 2013, the State Council issued the Action Plan for the Prevention and Control of Air Pollution, taking multiple measures to prevent and control air pollution. From the rectification and closure of key industries, to the comprehensive rectification of small boilers, the control of motor vehicle ownership, the control of catering pollution, and then to the vigorous development of clean new energy. A series of measures soon showed results, the air quality in key areas of China improved significantly, and the heavily polluted weather was greatly reduced. In 2017, the first national survey of pollution sources provided an overall understanding of the emission reduction effect, but it is still unclear how these emission reduction measures affect the emission of harmful trace elements in China’s atmosphere, their exposure concentration levels and related health risks.

“The treatment measures in the ‘Ten Atmospheric Rules’ and the survey around this measure mainly focus on conventional air pollutants such as particulate matter, sulfur dioxide and nitrogen oxides, in fact, we should also pay attention to the toxic and harmful trace elements that are more harmful to human health, such as arsenic, lead, cadmium, etc.” Tian Hezhong told China Science News, “Based on the fusion of multi-source data, this study establishes a gridded air emission inventory model of toxic and harmful trace elements in China, evaluates the driving force of different emission control measures on the emission changes of toxic and harmful trace elements in various departments, provinces and regions, and uses the atmospheric transport model and exposure risk evaluation model to quantitatively analyze and study the impact of emission changes in typical industries on the exposure concentration and health risks of harmful trace elements.” ”

The benefits of “coordinated emission reduction” are obvious

“In general, the emission reduction of toxic and harmful trace elements during the implementation of the ‘Ten Atmospheric Rules’ has achieved remarkable results, but its risks are still worth paying attention to.” Tian Hezhong said.

By investigating and studying the point source emissions of typical industrial emission sources such as coal-fired power plants, ferrous metal smelting, non-ferrous metal smelting, cement production, and waste incineration power plants in China, as well as the spatial distribution of coal consumption and installed capacity in different provinces, the researchers found that the emissions of harmful trace elements in China’s five major urban agglomerations (North China Plain, Yangtze River Delta, Pearl River Delta, Sichuan-Chongqing and Fenwei Plain) accounted for 42% of the total emissions in China. In addition to the five major urban agglomerations, Hunan, Inner Mongolia, Yunnan, Liaoning and Henan Provinces are also provinces with high emissions of harmful trace elements. During the “Ten Atmospheric Rules”, the average annual exposure concentration of 11 harmful trace elements in China decreased by about 28.1%. Among them, emission reductions in the coal-fired sector have driven the reduction of cobalt, arsenic, selenium, chromium and zinc concentrations the most significantly, contributing more than 50%; Changes in emissions from the ferrous metal smelting sector have led to reductions in cadmium and lead concentrations.

“Despite this, toxic and harmful trace element pollution in China in 2017 was still serious. Higher trace element concentrations are concentrated in parts of eastern China, north and southwest China. Liu Shuhan, the first author of the paper and an associate researcher at the State Key Laboratory of Marine Resources Utilization in the South China Sea at Hainan University, said, “In addition, the national average annual concentration of hexavalent chromium is 15 times higher than the national air quality standard, with the maximum value occurring in Shandong Province.” The concentrations of arsenic and nickel were slightly above the standard limits in Shandong Province and Shanghai. ”

The study found that during the “Atmospheric Ten” period, the national average annual carcinogenic risk of 7 carcinogenic elements decreased by about 39.5%. Among them, cobalt, hexavalent chromium and arsenic recorded the largest declines. However, in 2017, the average annual carcinogenic risk value of harmful trace elements still exceeded the threshold, and the higher carcinogenic risk mainly occurred in eastern China. The carcinogenic risks of arsenic and nickel in Shandong and Shanghai reached 9 times and 1.6 times the risk thresholds, respectively.

The scenario analysis shows that changes in emissions from the coal-fired sector led the reduction in carcinogenic risk from 2012 to 2017, resulting in a 1.5×10-6 reduction in carcinogenic risk. Changes in emissions from the ferrous and non-ferrous metal smelting sectors led to a decrease in carcinogenic risk of 0.8×10-6 and 0.3×10-6, respectively.

“The ‘Ten Atmospheric Rules’ mainly target conventional pollutants such as PM2.5, but they have played a good ‘synergistic emission reduction benefit’ for harmful trace elements.” Tian Hezhong explained, “The upgrading of dust removal, desulfurization and denitrification processes in key industrial industries such as the ultra-low emission transformation of coal-fired power plants has also reduced harmful trace element emissions. ”

Multi-source data fusion is powerful

“The implementation of the ‘Ten Atmospheric Rules’ not only has a significant effect on emission reduction, but also promotes the disclosure of relevant information in various industry sectors, which provides us with a lot of basic data for quantitative research.” In addition, the development of geographic information technology, digitalization and artificial intelligence technology has also made it possible for us to use ‘multi-source data fusion’ to conduct more refined ‘point sourced’ research. Tian Hezhong said.

In the past, the data source was single, and macro data such as statistical yearbooks usually did not show the specific location of emission sources. In recent years, with the increasing degree of information openness in various industries, provinces, regions, industries, enterprises, and even some associations and organizations will disclose information and data on some key emission sources from different perspectives. Although these data originate from different departments, serve different objects, and even have different data focus, statistical methods, and presentation methods, after data cleaning and technical processing, these data from different sources can complement each other for verification.

“For example, the statistical yearbooks and monthly statistical bulletins of each province have annual and monthly cement production data, and we will combine local economic data, combined with relevant data information such as water, coal, electricity, etc., and the allowable discharge amount of pollution discharge permits, etc., through multi-channel analysis and research to find out its emissions.” Tian Hezhong added, “Understanding what production process equipment an enterprise uses, mastering its dust removal, desulfurization, denitrification technology path, knowing how much coal and raw materials it consumes, etc., you can establish a set of technical methods to account for how much arsenic, lead, cadmium and other elements it emits, which is ‘multi-source data fusion’.” ”

Using these data, the researchers accurately locate the latitude and longitude of key industrial sources such as major coal-fired power plants, ferrous smelting, nonferrous smelting, cement production, and waste incineration in China, use various direct and indirect data, combined with local GDP, population, land use, traffic flow and other data, and then use mathematical statistical analysis methods to accurately calculate the emissions close to the actual emissions through sampling verification such as field research and on-site measurement, and accurately locate them on the grid.

“The health risks of heavy metal components are a prerequisite for fine control of air pollution.” The paper’s anonymous reviewer commented, “The innovative contribution of this paper is to provide up-to-date emission inventories and health risk estimates. Based on an evaluation of the benefits of specific measures, the study provides key insights for mitigating toxic and harmful trace element contamination and associated health risks. It provides a scientific basis for the precise control of toxic trace elements under China’s clean air and low-carbon policies, and also provides a reference for other countries and regions to quantify trace element emissions. (Source: Zhang Shuanghu, China Science News)

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