Study: Sea Salt Worsens Coastal Air Pollution
Air pollution in the world’s busiest ports and shipping regions may
be markedly worse than previously suspected, according to a new study
showing that industrial and shipping pollution is exacerbated when it
combines with sunshine and salty sea air.
The paper, “High levels of nitryl chloride in the polluted subtropical
marine boundary layer,” is available in the April 6 advance online
edition of the journal Nature Geoscience at
http://www.nature.com/ngeo/journal/vaop/ncurrent/index.html. The print
version is scheduled to appear on May 1. In the study, a team of researchers that included University of Calgary (U of C) chemistry
professor Hans Osthoff report that the disturbing phenomenon
substantially raises the levels of ground-level ozone and other
pollutants in coastal areas.
“We found unexpectedly high
levels of certain air pollutants where pollution from cities and ships
meets salt in the ocean air along the southeast coast of the United
States,” said Osthoff, who joined the U of C’s Department of Chemistry
last August. “It only makes sense that this is a problem everywhere
industrial pollution meets the ocean, as is the case in many of the
largest cities around the world. It also changes our view of the
chemical transformations that occur in ship engine exhaust plumes, and
tells us that emissions from marine vessels may be polluting the globe
to a greater extent than currently estimated.”
Osthoff was
part of a National Oceanic and Atmospheric Administration (NOAA) team
that spent six weeks monitoring air quality in busy shipping areas off
the southeastern coast of the United States between Charleston, South
Carolina and Houston, Texas, in the summer of 2006. The researchers
found unexpectedly high levels of nitryl chloride (ClNO2), a chemical
long suspected to be involved in ground-level ozone production along
the coast. They then determined that the compound is efficiently
produced at night by the reaction of the nitrogen oxide N2O5 in
polluted air with chloride from sea salt. With the help of sunlight,
the chemical then splits into radicals that accelerate production of
ozone and, potentially, fine particulate matter, which are the main
components of air pollution. Their findings also show that up to 30 per
cent of the ground-level ozone present in seaside cities such as
Houston may be the result of pollution mixing with salt from ocean mist.
Osthoff said he intends to continue to work on halogen compounds at the University of Calgary.
"The
Texas study covered only a very limited geographic area. We would like
to find out to what extent this chemistry affects air quality in other
regions, for example, the the Greater Vancouver area, or the Arctic,”
he said. “Our study indicates that halide salts such as chloride or
bromide, which have been thought of as being relatively inert, may be
playing a much greater role overall in the lower atmosphere."