In a recent study, researchers found that while the western U.S. has warmed, recently observed warming in the mountains of the western U.S. likely is not as large as previously supposed. The results, published online Jan. 13 in Geophysical Research Letters, show that sensor changes have significantly biased temperature observations from the Snowpack Telemetry (SNOTEL) station network.
Secretary of the Interior Sally Jewell discusses working with Congress, climate change, and scientific integrity during talks at the American Geophysical Union's Fall Meeting.
In rural Alabama, as in the rest of the country, human-made aerosols reduce visibility. Particles are in the atmosphere year round, but in the humid summer season, the concentration of pollutants--and their effects--is at a peak. In addition to making the air murky, aerosols are bad for human health. A new study investigates the historical trend of these effects.
Across the nation, emissions of an important aerosol precursor are on the decline: From 1990 to 2010, the country saw a 60 percent reduction in sulfur dioxide emissions, thanks to the 1990 Clean Air Act Amendments. In Alabama, the past decade has brought reductions of nearly 10 percent per year. Volatile organic compounds are the other major contributor to aerosols in the southeastern United States. These predominantly come from biogenic sources in the southeastern United States and have decreased much more slowly. Overall, total aerosol mass is decreasing and its relative composition is changing.
With this in mind, Attwood et al. measured aerosol optical extinction as a function of humidity using a spectrometer in an Alabama forest. Researchers used the site and its climate as representative for the southeastern United States. Combined with historical data, they created a picture of how particles that contain less sulfate, which originates from sulfur dioxide, absorb less water. Visibility is improving in the southeastern United States, both because there is less aerosol mass and because the aerosol is becoming less water absorbing.
The calculated improvement in visibility due to decreasing aerosol mass is 3.4 percent per year during the period 2001 to 2013, with changing water absorption accounting for an additional 1.1 percent per year improvement. This dramatic change has been confirmed using satellite records of aerosol optical depth and visibility records at airports.
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