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This week from AGU: Pacific wind patterns, Ethiopia's sedimentary record, US air quality

American Geophysical Union

From AGU's blogs: Wind pattern behind California's drought also struck at ocean food chain

Unusual weather that contributed to the California drought also led to an unprecedented drop in small plant-like organisms in the northeastern Pacific Ocean that form the base of the ocean food chain, potentially affecting fish, birds and marine mammals, according to a new study published in Geophysical Research Letters, a journal of the American Geophysical Union.

From Reading History From Afar

A look at the sedimentary record in northern Ethiopia tells the story of oceans past--and maybe future.

From AGU's journals: Changing patterns in U.S. air quality

Over polluted mid-latitude regions, monthly mean ground-level ozone peaks during the summer, with ozone production fuelled by regionally emitted nitrogen oxides (NOx), abundant biogenic volatile organic compounds (VOCs), and sunlight.

Using a global chemistry-climate model to simulate ozone during the 21st century, Clifton et al. show that the seasonality of ground-level ozone could reverse over the northeastern United States before midcentury. They attribute this shift to large reductions in eastern U.S. NOx emissions. Observations indicate this shift is already happening because the summertime peak has broadened in recent years.

Nitrogen oxides are produced as a by-product of combustion--high temperatures cause nitrogen and oxygen in the atmosphere to react. Photochemical reactions involving NOx and VOCs, including methane, contribute to the formation of ground-level ozone. Although ozone plays an important role in the upper atmosphere as a shield against ultraviolet radiation, at ground level it is a hazardous pollutant.

The authors find that doubling global methane, a strong, well-mixed greenhouse gas and precursor to baseline levels of ozone, increases monthly mean ground-level ozone during all months--especially wintertime and early spring, when the ozone lifetime is longest. Thus, although NOx reductions change the shape of the northeastern U.S. ground-level ozone seasonal cycle, rising methane amplifies the winter-spring peak.

In the absence of changes in ozone precursor emissions, global climate warming is expected to increase peak summertime ground-level ozone. Additional regional NOx emission reductions can mitigate this adverse effect of climate warming on summertime ozone pollution.


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