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Plant pollen may help clouds form, impacting climate change

Seasonal allergies are a yearly struggle for millions of people worldwide, and it seems that climate change is only making matters worse. A recent study published in ACS Earth and Space Chemistry demonstrates that common allergen-producing plants, such as ryegrass and ragweed, emit more “sub pollen particles” (SPPs) than previously thought. 

Interestingly, these plants are more likely to impact climate through their intact pollen grains, which can boost cloud formation. Pollen, aside from being a nuisance to allergy sufferers, is essential for plants to exchange genetic material and reproduce. 

Pollen and SPPs

When exposed to moisture, pollen grains can burst into tiny SPPs that are less than a micron long. Due to their smaller size, SPPs can reach the lower respiratory system, where they persist longer and cause more inflammation than their larger counterparts.

Both SPPs and whole pollen grains are thought to act as ice nucleation sites, which are miniature starting points for clouds. 

However, SPPs and pollen form smaller, more numerous clouds that tend to retain their precipitation. It then traps radiant heat, contributing to climate change. Higher temperatures can then extend pollen-release periods, further aggravating the issue.

Brianna Matthews, Alyssa Alsante, and Sarah Brooks previously investigated how oak trees emit SPPs at different humidity levels. 

How the study was done

In their new study, the researchers wanted to examine how two other common allergen-producing plants – ragweed and ryegrass – release SPPs under humid conditions and how these particles could affect ice cloud formation.

The experts collected samples of ryegrass and ragweed and placed them into a specialized “pollen chamber.” They exposed the samples to different humidity levels and bursts of wind over several hours to simulate real-world conditions. 

By assessing the number of SPPs per pollen grain and the ice nucleation abilities of both, the team made a surprising discovery.

What the researchers found

Their findings revealed that previous experiments on the same types of plants had underestimated the number of SPPs by a factor of 10 to 100. The researchers attributed this discrepancy to the less realistic methods used in earlier studies to spread the pollen and generate SPPs.

However, the experts also found that ragweed and ryegrass SPPs were very poor ice-nucleating sites, barely better than plain water. 

In contrast, whole pollen grains facilitated cloud growth. These updated parameters and numbers of emitted pollen grains and particles could ultimately be used to create more accurate climate models.

In summary, this research not only highlights the underestimated impact of allergen-producing plants on seasonal allergies but also emphasizes the need for accurate data on pollen emissions to better understand their role in climate change.

More about pollen and SPPs

Pollen is a fine powder-like substance produced by plants as part of their reproductive process. It contains the male gametes (sperm cells) of seed plants, and its primary function is to fertilize the female ovules, leading to the formation of seeds. 

Pollen grains are produced by the male parts of a plant, called the stamen, and are typically transferred to the female reproductive organs either by wind, insects, or other animals.

Pollen can cause allergic reactions in susceptible individuals. When inhaled, pollen can trigger an immune response in the body, leading to symptoms such as sneezing, itching, watery eyes, and a runny or stuffy nose. This condition is commonly referred to as seasonal allergies or hay fever.

Subpollen particles (SPPs) are smaller fragments that are formed when pollen grains are exposed to moisture and subsequently burst. These tiny particles, which are less than a micron in size, can reach deeper into the respiratory system than intact pollen grains. 

Due to their small size, SPPs can last longer and cause more inflammation in the lower respiratory system, potentially exacerbating allergy symptoms.

Recent research has shown that allergen-producing plants like ragweed and ryegrass emit more SPPs than previously thought. This increased emission of SPPs has implications not only for allergy sufferers but also for our understanding of climate change.

Both intact pollen grains and SPPs can act as ice nucleation sites, which serve as starting points for cloud formation. However, SPPs and pollen create smaller, more numerous clouds that tend to retain their precipitation instead of releasing it. 

This process traps radiant heat, contributing to climate change. Additionally, higher temperatures caused by climate change can extend pollen-release periods, further exacerbating allergy issues.

Understanding the role of pollen and SPPs in the environment is essential for creating more accurate climate models and addressing the impacts of allergen-producing plants on public health.


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