>Ronald Cohen


>Found: the Missing Nitrogen Oxides


>Ron Cohen is a Professor in the Departments of Chemistry and of

>Earth and Planetary Science at UC Berkeley. He is also one of the

>founding members of the UC Berkeley Atmospheric Sciences Center.

>Ron's research links all of these different disciplines in an effort

>to understand the chemical processes that affect stratospheric

>ozone, air quality and climate. He develops new analytical methods

>(often using lasers) to measure the composition of the atmosphere.

>Using these new tools he has made measurements from aircraft over

>Antarctica and Greenland and from ground stations in Nashville,

>Houston, and in the Sierra Nevada.


>Ron will describe some recent observations and describe their

>implications for air quality. If time permits, Ron will also discuss

>his research on the atmospheric effects of jet contrails.


Ron began his talk by explaining that his group is trying to develop more accurate detailed information on the atmosphere and human effects on it than had previously been obtained. To accomplish this, he and his grad students have designed a number of new instruments, and visited a number of out of the way places like Greenland.

He then showed us a chart of measured impacts of climate change to date. These were a slight warming of most of the United States, and a cooling of the area between Texas and Florida along the gulf coast, and up to about the Mason-Dixon line. He explained that area was cooling because of changes in air flow patterns. After that he talked a bit about the biggest factors in human caused air pollution.

Ozone is only in the atmosphere for a week or two after it is emitted, but because large amounts of it are produced by burning every day, it is a significant problem. He showed a map of North America, and surface Ozone was worst around the big cities. In a map of Northern California, the worst hot spots were around Sacramento and other central valley cities. Even farm country ozone levels are worse than the bay area's, probably because of the farm equipment that burns diesel without any emissions control equipment. Another chart showed that Ozone concentration in the atmosphere is also very concentrated around heavy driving times, experiencing a peak during evening rush hour.

Carbon Dioxide is less dangerous on a chemical basis, but once it is emitted it will spend something like 75 years in the atmosphere before it is finally absorbed by the oceans. Because of this its effect on us is much more fairly distributed, coming through as slight changes in the temperature for everybody. Dr. Cohen pointed out that there has never been such a sudden impulse of carbon dioxide into the ocean ecosystem as the one we have started since the industrial revolution started about 150 years ago. It is completely unknown what the impact of that will be.

Nitrous Oxides are a much more interesting problem, and one that he has spent a lot of time observing. Dr. Cohen showed us some pictures of a rack mounted instrument that they had designed to measure nitrous molecules in the air. It worked by shining a 640 nm Laser on the air, in which Nitrogen containing molecules respond to by emitting orange light. He was able to use it to measure nitrogen containing compounds. The machines have been installed in a variety of locations to gather information on atmospheric composition.

Cohen explained that nitrous gasses are byproducts of combustion that is done poorly. (Good combustion only produces carbon dioxide and water.) NO3 like molecules bounce around in the atmosphere turning light into heat until they decompose into nitric acid, which rapidly combines with water and falls as acid rain. On the east coast, half of the acid in acid rain is this stuff, the rest is sulfuric acid which comes from burning dirty coal. On the west coast there is much less sulfuric acid in our rain because we don't use much coal.

Points that came out during the Q&A that followed the talk:

Dr. Cohen explained that jet contrails are not a significant factor in changing the composition of our atmosphere.

The main source of sulfur in the west coast air is the exhaust of cargo ships, because they use about the cheapest forms of diesel available.

Because the increase in CO2 in the atmosphere caused by human activity is only on the order of hundreds of parts per million, meaning a tiny percentage change, there is no correlation between this and the breakdown in the ozone layer over antarctica.

Tian Harter