Identifying pollutant origins: combustion vs. historical emissions in Yangtze River Estuary air

A detailed atmospheric study in the Yangtze River Estuary has successfully distinguished the sources of harmful polychlorinated biphenyls, or PCBs, in the air. Researchers led by Tian Lin from Shanghai Ocean University, in collaboration with scientists from the Chinese Academy of Sciences and Fudan University, found that nearly one-third of these persistent pollutants originate from active combustion, while the majority comes from non-combustion sources, including historical industrial materials.

A Year of Atmospheric Monitoring

To understand the behavior of these pollutants, the scientific team collected air samples for one year at a remote monitoring site on Huaniao Island, a background location influenced by air masses from the heavily industrialized Yangtze River Delta. The samples were analyzed for 34 types of PCBs, as well as for organic carbon and elemental carbon, which are well-known byproducts of burning processes like fossil fuel combustion and biomass burning.

Contrasting Seasonal Pollution Patterns

The investigation revealed distinct seasonal changes in pollutant levels. Concentrations of PCBs in the gas phase were highest in the summer, when warmer temperatures cause these chemicals to re-volatilize from soil and water surfaces back into the atmosphere. In contrast, PCBs attached to airborne particles were more abundant in colder seasons, along with higher levels of organic and elemental carbon. This wintertime increase is linked to emissions from burning fuel for heating and the frequent occurrence of regional haze.

A New Method for Source Apportionment

The researchers applied a statistical model called Positive Matrix Factorization to their extensive dataset. By analyzing the relationships between different PCB types and the carbon markers, the model could separate the pollutants into different groups based on their likely origin. This approach allowed the team to quantify the contributions from both combustion and non-combustion pathways, offering a clearer picture of PCB sources in the region.

The Contribution from Combustion

The analysis determined that 30 percent of the airborne PCBs came from combustion sources. The model identified two specific types of burning activities. One was high-temperature processes, such as the dismantling of electronic waste, which is common in some coastal areas of China. The other was lower-temperature combustion, including the burning of coal for regional heating in winter and straw burning in summer.

Legacy Pollutants and Long-Range Transport

The remaining 70 percent of PCBs were attributed to non-combustion sources. A significant portion of these pollutants consists of weathered mixtures of industrial PCBs, like Aroclors, that were used decades ago in products such as electrical equipment and plastics. These legacy chemicals re-enter the atmosphere from contaminated sites. Another source identified was the long-distance atmospheric transport of desert dust, which can carry less-chlorinated PCBs to the estuary, particularly during springtime dust events.

Improving Air Quality Strategies

This work provides valuable information for managing persistent organic pollutants. By using carbon particles as a tracer, the study led by Tian Lin and Zhigang Guo offers a robust method to differentiate between ongoing emissions from burning and the re-emission of historical contaminants. This improved understanding of pollutant sources can assist in developing more targeted and effective air quality regulations. The authors note that further research is needed to fully understand how certain atmospheric particles influence the transport of these chemicals over long distances.

Corresponding Author:

Tian Lin

Original Source:

https://doi.org/10.1007/s44246-023-00046-4

Contributions:

Tian Lin: Resources, Conceptualization, Supervision, Writing–original draft. Wanqing Zhou: Writing, Data curation. Shizhen Zhao: Investigation, Data curation, Field surveys. Minqiao Li: Field surveys, Writing. Zhigang Guo: Resources, Conceptualization, Supervision. All authors read and approved the final manuscript.