Highlights of Recent Research on Atmospheric
USGCRP-sponsored research continues to advance understanding of
the causes, magnitude, and consequences of changes in stratospheric
ozone, UV radiation, and atmospheric chemistry. The FY96 edition of
Our Changing Planet included a summary of recent key findings.
Highlights of more recent findings follow:
- Atmospheric concentrations of ozone-depleting chemicals are starting
to decrease. Over the past few decades, global atmospheric
monitoring stations had reported the steady growth in the
concentrations of CFCs and other ozone-depleting chemicals. Recent
observations have not only shown a slowdown in growth, but also
are revealing, for the first time, decreasing concentrations. These
downward trends are the first observed atmospheric response to the
international agreements to halt production of these ozone-depleting
- Year-to-year changes in the stratospheric ozone layer have been
explained. Superimposed on the observed overall downward decadal
trends in the ozone layer are variations over periods of a few years.
The long-term declines have been associated with the growth in the
use of ozone-depleting chemicals, such as CFCs, but the shorter term
changes have been unexplained. Recent theoretical modeling studies
have shown that these shorter term variations can be explained by
the augmented ozone depletion caused from the chemistry on
surfaces of particles resulting from episodic volcanic eruptions,
thereby providing a more complete picture of ozone layer changes.
- Soils may be a larger methyl bromide sink than previously thought.
Because methyl bromide is involved in the destruction of ozone in
the stratosphere, this finding suggests that management of soils may
have implications for the stratospheric ozone budget and the amount
of UV radiation that reaches the Earth's surface.
- Satellite data have confirmed, on global scales, the expected
stratospheric abundance's of ozone-depleting chemicals. Surface-level
stations have long monitored the lower atmospheric growth of
the ozone-depleting chemicals that are released into the atmosphere
by human activities. Balloon and airborne measurements have
tracked the resulting ozone-related chlorine and bromine compounds
in the stratosphere in particular regions. However, recent satellite
data have provided the first truly global look at these species and
have confirmed the picture of the human contributions to the global
budget of these ozone-related species.
- Carbon monoxide concentrations were measured from latitudes from
Alaska to the Antarctic using an instrument mounted in the Space
Shuttle on two flights in 1994. These measurements demonstrated a
capability for providing global data sets and measuring seasonal
variations. The measurements showed the expected higher levels
near the source regions, mainly in the Northern Hemisphere and near
areas of biomass burning in the tropics, but were also able to observe
the much lower concentrations over the Southern Ocean areas that
are seldom measured. Carbon monoxide affects the rate of
tropospheric chemical removal of other pollutants that affect the
concentration of tropospheric ozone, which is both a photochemical
oxidant and a greenhouse gas.