University of Iowa engineering researchers have found that chemicals widely used in personal care products, such as shampoos, lotions, and cosmetics, may not persist in the atmosphere as long as previously thought. 

Researchers incorporated new chemical reactions and temperature effects into global chemistry models, discovering that volatile methyl siloxanes or VMS typically last 2.7 to 6.7 days, significantly shorter than earlier estimates.

"One of the most exciting aspects of this project, for me, was seeing how the exchange of information between modelers and field researchers goes both ways,” said Christopher E. Brunet, a PhD candidate in civil and environmental engineering. “We relied on valuable data from previous sampling campaigns and laboratory experiments to build this model, and in turn, we learned new things about the behavior of these chemicals that we think will be helpful to them."

The findings have been published in Environmental Science & Technology, a leading journal in the field. Brunet is first author on the paper.

Another important discovery is that while these chemicals can travel long distances, their concentrations in remote regions such as the Arctic are lower than expected, averaging about 4.5 nanograms per cubic meter, compared to 160 nanograms per cubic meter in urban areas. By forecasting likely concentration ranges in advance, the model lets researchers plan their fieldwork and choose the right equipment for remote environments.

These findings suggest that environmental risks from long-range transport may be less severe than previously believed, though urban exposure remains high.

“We relied heavily on decades of foundational work by researchers at the National Center for Atmospheric Research and our collaborators who developed the halogen chemistry central to this model,” said Brunet, a graduate research assistant at IIHR—Hydroscience and Engineering. “This project simply would not have been possible without that."

The research team includes scholars from the College of Engineering (civil and environmental engineering and chemical and biochemical engineering), IIHR—Hydroscience and Engineering, a research center within the college, as well as external partners. Other contributors include Saeideh Mohammadi, Behrooz Roozitalab, Nora K. Gibson, Rafael P. Fernandez, Alfonso Saiz-Lopez, Keri C. Hornbuckle, and Charles O. Stanier.