Microplastics May Alter Weather Patterns

Researchers from Penn State have identified a new role for microplastics, which are now detected in various atmospheric conditions, as they may influence cloud formation and climate. This study, published in Environmental Science & Technology: Air, presents findings that microplastics act as ice nucleating particles (INPs), enabling the formation of ice crystals within clouds. This mechanism suggests that airborne microplastics could play a role in precipitation patterns and possibly impact climate and weather systems.

Laboratory evidence of microplastic influence on ice formation

To study this effect, the research team conducted experiments using four common types of microplastics: low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). By suspending these plastics in water droplets and cooling them, they observed that microplastics initiated ice formation at temperatures 5–10 degrees Celsius higher than droplets without such particles. Typically, pure water droplets freeze at approximately -38 degrees Celsius, but when microplastics were present, freezing occurred at temperatures as warm as -22 degrees Celsius.

The presence of microplastics in water droplets alters their physical structure, which promotes ice nucleation at relatively warmer temperatures. This change indicates that even low concentrations of microplastics in the atmosphere could shift ice formation dynamics in clouds, potentially altering cloud structure and precipitation levels.

Potential impact on precipitation and cloud dynamics

Microplastics' influence on cloud structure extends to various types of mixed-phase clouds, which contain both liquid water and ice. This includes cumulus, stratus and nimbus clouds, which are commonly found at diverse altitudes. When additional particles such as microplastics increase within these clouds, water availability is distributed across a greater number of droplets, resulting in smaller droplet sizes that may delay rainfall. As a result, clouds accumulate more water, ultimately leading to heavier rainfall when these droplets reach the size required to precipitate.

Further, microplastics might affect the balance between cooling and warming clouds based on the quantity of liquid water versus ice. The effects on global climate patterns could vary widely, depending on how these particles interact with cloud coverage, atmospheric conditions and weather events.

Environmental aging alters ice-nucleating ability of microplastics

Environmental aging, a process in which particles undergo chemical changes due to exposure to light, ozone and other atmospheric components, was simulated in the laboratory to examine its effects on microplastics. The study found that aging generally reduced the ice-forming capacity of LDPE, PP and PET but increased the ice-nucleating efficiency of PVC. These shifts in particle structure, which can result from long-term environmental exposure, indicate that aged microplastics may differ in their impact on cloud properties and atmospheric behavior compared to newly introduced microplastics.

Further investigation into plastic additives and climate modeling

The research team plans to explore how additives commonly found in plastics, such as plasticizers, might influence the nucleating properties of microplastics in the atmosphere. The presence of these additives could introduce new variables in understanding how microplastics interact with atmospheric systems and affect global weather patterns. Current climate models do not account for the role of microplastics as ice nucleators, meaning that any impacts of these particles on climate predictions may be underrepresented.

Reference: Busse HL, Ariyasena DD, Orris J, Freedman MA. Pristine and aged microplastics can nucleate ice through immersion freezing. ACS EST Air. 2024. doi: 10.1021/acsestair.4c00146

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