Atmospheric microplastics in China: from urban skies to typhoon transport - a multi-dimensional analysis of China's microplastic pollution challenge

Abstract

Microplastic (MP) pollution represents a widespread and complex environmental issue, carrying substantial consequences for ecosystems, human health, and policy development. This thesis provides a comprehensive assessment of MPs, focusing on their atmospheric presence, transport mechanisms, and management strategies, with a particular emphasis on China's urban and coastal areas.
The study begins with a critical literature review focusing on the underexplored role of atmospheric MPs transport, emphasizing their ability to travel long distances and accumulate in remote locations such as Polar Regions and mountain tops. The study explores different sources of MP by categorizing them based on their origin. Additionally, it attempts to explain the possible atmospheric transport and removal mechanism of MPs by identifying it as a part of the particulate matter. It further highlights the limitations associated with differences in sampling and analytical techniques, recommending development of standardized methodology. The study also reveals considerable variations in MP distribution due to factors such as population density, weather conditions, and air mass dynamics, while also identifying notable gaps in the understanding of their transport mechanisms, interactions, and health impacts. The study then discusses the interactions of MPs in the environment and their potential health impacts due to exposure. It underscores that due to the hydrophobic nature and small size along with higher surface area, MPs can adsorb several chemical and biological toxicities, thus increasing the bioavailability of these toxins in the food chain. The study then examines various exposure routes by which humans encounter MPs, including ingestion, inhalation, and dermal contact, corroborated by recent evidence of MP presence in human blood, lungs, and digestive systems. The inhalation of MPs poses health risks, as their diminutive size facilitates entry into lung alveoli, potentially resulting in inflammation or cancer via immune cell responses.
Furthermore, this study examines Suspended atmospheric microplastics (SAMPs) in Ningbo, China, a coastal metropolitan area. The quantified SAMPs ranged from 0.02 to 0.43 items/m³, with an average of 0.14 ± 0.09 items/m³. Urban centres demonstrated SAMP concentrations that were 70% higher than those in rural areas, with rayon and polyethylene terephthalate identified as the primary polymers associated with local industrial activities. Seasonal variation followed a winter > autumn > spring > summer pattern. Correlation and principal component analyses revealed that atmospheric temperature, pressure, wind speed, and rainfall are significant factors affecting SAMP abundance. Backward trajectory analysis indicated that oceanic air masses reduced SAMP levels, whereas terrestrial air contributed to increased pollution.
The study further examines deposited atmospheric microplastics (DAMPs) in Ningbo and across 30 Chinese cities, finding an average DAMP flux of 473.9 ± 349.3 items/m²/day in Ningbo. In China, the annual deposition of DAMP was estimated to be around 0.306 million tons, exhibiting notable regional variations associated with population density, GDP, and meteorological factors. The nationwide analysis of DAMPs further revealed that Coastal cities have greater MP sizes and higher deposition rates attributable to marine influences, underscoring the significance of rainfall as a vital scavenging mechanism. The study further explored the relationship between SAMPs and DAMPs to understand the effectiveness of rainfall in MP removal, which revealed a washout ratio of (1.02 ± 0.42) × 10⁶, and an inverse relationship between SAMPs and DAMPs. Implying that rainfall can effectively scavenge suspended MPs as deposited MPs.
The study further explored and established a novel relationship between MP pollution, extreme weather events such as typhoons and climate change by examining the deposition of MPs during three typhoon events in eastern China (2023-2024). During typhoons, atmospheric deposition samples demonstrated a significant increase in MP deposition rates (6,291-12,722 items/m²/d), followed by a significant decrease in the post-typhoon period. High-density polymers, including polyethylene terephthalate and polyvinyl chloride, were identified, indicating potential resuspension from ocean depths. Backward trajectory analysis confirmed the transport pathways from ocean to land, while a feedback loop was established that links MP pollution, ocean thermal properties, and intensified typhoon activity driven by climate change.
The study then consolidates the results of three case studies to provide an integrated discussion on the spatial and temporal variations of atmospheric MPs. It explores the influence of environmental processes, anthropogenic factors, and climatic variability on MP distribution and preservation, highlighting significant insights related to both chronic emissions and episodic events, such as typhoons. The discussion contextualizes these findings within broader scientific frameworks, explores interlinkages across scales, and evaluates their implications for MP transport, deposition, and management.
Finally, the thesis investigates strategies for mitigating MP pollution, with a focus on plastic waste reduction using the 4Rs (Reduce, Reuse, Recycle, and Recover), upcycling, and the development of sustainable alternatives. The complex characteristics of MP pollution require a comprehensive strategy that combines innovative remediation technologies, strong regulatory measures, and global cooperation. Additionally, the findings underscore the necessity for focused policy interventions in densely populated and industrialized areas. This thesis highlights critical knowledge gaps and advocates for the incorporation of MPs into air quality standards, climate models, and waste management policies to effectively mitigate their environmental and health risks.
This study enhances our comprehension of atmospheric pollution by providing novel relationships between environmental, socioeconomic and meteorological factors and provides actionable insights and evidence-based strategies, and policies, establishing a framework for understanding and mitigating MP pollution, thereby contributing to global efforts to address a significant environmental challenge.

Date of Award	13 Jul 2025
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Jun He (Supervisor), Faith Chan (Supervisor) & Hang Xiao (Supervisor)