In the post just prior to this one, I wrote about trees dying in Alaska, which has been attributed to warming and its drying effects from climate change. I wrote to the researchers of the study because that strikes me as an inadequate explanation, since birch, aspen and pines are to be found in areas much further south, with longer growing seasons. In response, I received this reply from one of the scientists who published the study:
"Dear Gail,Attached is a picture of an Alaska birch tree on the University of Alaska Fairbanks campus with severe acute drought stress symptoms, and this tree is at risk of dying.
Other trees nearby appear to be dead, although we need to wait until next spring to see if any leaves at all appear to be certain that they have died.Tropospheric ozone is an issue in forest health and survival near population centers and industrial sources of emission, but not currently an issue here in Alaska or most of the boreal forest.Thank you,Glenn Juday"
Hold on! These forest ecologist types need to confer with their scientific colleagues who are current with the study of atmospheric physics and chemistry. By way of countering his insouciance, I have uploaded some maps that were linked to in a comment from JohnG, on an earlier post.
The title of a 2002 article from the NASA publication, Earth Observatory, "Highways of a Global Traveler - Tracking Tropospheric Ozone" kind of says it all. They are matching models with actual measurements from satellites, and it is quite clear that ozone, even back then, is not confined to urban locations, and in fact moves from one continent to another.
"Before scientists began to track the global travels of ozone in the troposphere with satellite data and measurements made from aircraft, they assumed that much of that part of the atmosphere was relatively free of ozone. But after combining satellite observations with data-rich models that simulate the atmosphere’s chemistry and dynamics, they are finding tropospheric ozone in some unexpected places. Tropospheric ozone turns out to be an intercontinental traveler, crossing geographic and political boundaries...The lifetime of ozone’s precursors in the troposphere is sufficiently long that they can produce ozone hundreds or even thousands of miles away before further chemical reactions transform ozone into oxygen and other chemicals...Other major air circulation patterns appear to carry ozone from one continent to another. Although a complete, detailed, global picture of how natural and human activities on one continent influence the air quality over other continents and oceans requires more research, some trends are becoming clearer. According to modeling studies at Harvard University, background concentrations (amounts that are usually there) of ozone in surface air over the United States range from 25 to 55 parts of ozone per billion parts of air (ppb) and can be largely attributed to transport from outside the United States. This amount of ozone is significant for a country where the national air quality standard is 80 ppb over 8 hours, not to be exceeded more than three times per year. The same Harvard study had implications particularly for the western part of North America, which receives more pollution from Asia than the eastern part does. In fact, if people in North America succeeded in reducing their emissions of nitrogen oxides and hydrocarbons (ozone precursors) by 25 percent, the expected tripling of Asian emissions by 2010 could more than offset that North American effort."
From Science 101: Air Pollution - At Home and Around the Globe - This map estimates deaths from Ozone - Alaska is the same level as the rest of the continental US. This is human deaths - but there is no reason to think trees deaths would be distributed any differently.
Sure looks to me like ozone finds its way to Alaska!
Another NASA presentation, "The Influence of Tropospheric Ozone on Arctic climates" has the following slide:
and these comparative maps, which indicate such a terrifying rate of increase I hate to think what has happened in the last 20 years:
It is possible to waste prodigious amounts of time checking out maps at the NASA Goddard Home Page for Tropospheric Ozone! I've only just begun to investigate, but I wanted to share these colorful images without delay:
And finally, a brief video clip - this is just nitrogen dioxide in the atmosphere. It doesn't take into account other ozone precursors or acid rain, clouds and other wet deposition.