In the popular children’s story “Horton Hears a Who!” author Dr. Seuss tells of a gentle and protective elephant who stumbles upon a speck of dust that harbors a community of microscopic creatures called the Whos living the equally tiny town of Whoville. Throughout their journey together, Horton argues for the existence of the Whos traveling around in the air on a dust speck, while doubters dispute the finding. Ultimately, through observation, evidence for the organisms emerges, but regardless of the outcome, this speck altered a world greater than its own.
While this tale is a work of fiction, climate and atmospheric scientists have considered a real-life Whoville scenario — biological particles and inorganic material riding around in the atmosphere affecting the climate. Previous research has shown that some aerosols are very good at nucleating ice, which could form clouds in the troposphere. But due to complex atmospheric chemistries and a lack of data, scientists aren’t sure what percentage of these ice active particles are biological in nature and abundant enough in the troposphere to have an impact on climate. Furthermore, chemically parsing the metaphorical Whos from their speck has proved difficult — until now.
In the popular children’s story “Horton Hears a Who!” author Dr. Seuss tells of a gentle and protective elephant who stumbles upon a speck of dust that harbors a community of microscopic creatures called the Whos living the equally tiny town of Whoville. Throughout their journey together, Horton argues for the existence of the Whos traveling around in the air on a dust speck, while doubters dispute the finding. Ultimately, through observation, evidence for the organisms emerges, but regardless of the outcome, this speck altered a world greater than its own.
While this tale is a work of fiction, climate and atmospheric scientists have considered a real-life Whoville scenario — biological particles and inorganic material riding around in the atmosphere affecting the climate. Previous research has shown that some aerosols are very good at nucleating ice, which could form clouds in the troposphere. But due to complex atmospheric chemistries and a lack of data, scientists aren’t sure what percentage of these ice active particles are biological in nature and abundant enough in the troposphere to have an impact on climate. Furthermore, chemically parsing the metaphorical Whos from their speck has proved difficult — until now.
Atmospheric science researchers in the Program in Atmospheres, Oceans and Climate (PAOC) in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) have found a way to differentiate biological material in the atmosphere (bioaerosols) from non-biological particulates with a higher accuracy than other methods, using machine learning. When applied to previously-collected atmospheric samples and data, their findings support evidence that on average these bioaerosols globally make up less than 1 percent of the particles in the upper troposphere — where they could influence cloud formation and by extension, the climate — and not around 25 to 50 percent as some previous research suggests.
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Photo: Graduate student Maria Zawadowicz is researching the interrelationship of particulate matter and cloud formation in the Cziczo Lab. Credits: Kent Dayton
