|
Researchers
at Harvard University and the University of British Columbia (UBC) have
provided visual evidence that atmospheric particles—which are
ubiquitous, especially above densely populated areas—separate into
distinct chemical compositions during their life cycle.
The
observations could have important implications for modeling global
climate change and predicting air quality conditions. The tiny
particles, which form part of an airborne chemical mix above cities,
play a role in pollution by providing a surface for chemical reactions
and in climate by reflecting and absorbing solar radiation and by acting
as seed surfaces for water condensation and cloud formation.
“We’ve
confirmed experimentally that changes in relative humidity can separate
the organic and inorganic material in individual atmospheric particles
into distinct liquid phases, much like oil separates from water,” says
UBC professor Allan Bertram, director of the collaborative research and
training program on atmospheric aerosols at UBC and co-principal
investigator on the paper.
“Having
two liquid phases rather than one can change the rates of chemical
reactions on particles, may change the amount of light the particles
reflect and absorb, and impact their ability to act as seeds for
clouds.”
The
findings, which used air samples from Atlanta, Georgia, the Harvard
Environmental Chamber, and the Pacific Northwest National Laboratory
Environmental Chamber—have been published in the Proceedings of the National Academy of Sciences.
“I
think of it as the beautiful phenomenon when I mixed food coloring,
water and vegetable oil in a bottle when I was in grade school,” says
Harvard researcher Scot Martin, Gordon McKay Professor of Environmental
Chemistry at the School of Engineering and Applied Sciences and the
Department of Earth and Planetary Sciences, and co-principal
investigator for the study.
“More
to the point, this phenomenon is really new thinking in the atmospheric
sciences, and it completely changes the way we need to think through
the reactive chemistry of atmospheric particles, a key component of
urban air quality,” Martin adds.
The
air in most urban environments contains particles that are mixtures of
organic molecules and chemicals like sulfates. When examined, samples
from Atlanta revealed distinct liquid phases that were qualitatively
similar to idealized particles generated in the laboratory. The
liquid-liquid phase separation occurs naturally.
Particulate
air pollution is a relatively new area of study, but one of growing
concern to researchers, health officials and environmental groups.
Increases in the concentration of aerosols are correlated with increased
health issues, including cardiopulmonary disorders.
“We
need to understand as much as possible about the chemical composition,
physical properties and interactions of atmospheric particles if we’re
going to assess how they impact human health, regional weather patterns,
and even global climate change,” notes Bertram.
Martin’s
and Bertram’s coauthors include Mackenzie L. Smith at Harvard SEAS;
Yuan You, Lindsay Renbaum-Wolff, Sarah J. Hanna, and Saeid Kamal at UBC;
Marc Carreras-Sospedra and Donald Dabdub at the University of
California, Irvine; Naruki Hiranuma and John E. Shilling at Pacific
Northwest National Laboratory; and Xiaolu Zhang and Rodney J. Weber at
Georgia Institute of Technology.
The
research was partly funded by the Natural Sciences and Engineering
Research Council of Canada through the Collaborative Research and
Training Experience (CREATE) program. The research was also funded by
the Atmospheric Chemistry Program of the U.S. National Science
Foundation, the Atmospheric System Research (ASR) Program of the
Department of Energy, and Pacific Northwest National Laboratory Aerosol
Climate Initiative.
Source: Harvard University
