The PM10 and PM2.5-Question.

In the fine dust debate there is a so called PM10-Standard and a PM2.5-Standard.

In Germany there is used the PM10-Standard in the publications about the existing air quality.

In 1997 the U.S. President signed a presidential directive to establish the 2.5PM-Standard for metering fine dust in the air:
"In a directive signed on July 16, President Clinton
ended the sharp debate between the Environmental
Protection Agency and its critics in and outside the
administration. EPA got, with only minor exceptions,
the goals that it had originally proposed last
November. But it gave some ground in the timetables
for the standards and the process of achieving them.
The new standards do three things. They reduce
the permissible concentrations of ground-level ozone.
They continue the present rules for coarse particulate
matter in the air. And they set a new standard for fine
particulate matter—particles with a diameter of 2.5
microns (PM2.5). (...) Since it believes a
substantial death rate attaches to PM2.5, it may want to
consider taking action sooner than 2005."
Anderson, J.W.
New Air Quality
Standards Are Tighter but Compliance Is Distant
in: RESSOURCES, FALL 1997/ISSUE 129 Page 6
http://www.rff.org/Documents/Resources/Resources-129_Anderson.pdf

Although there is no metering with the PM2.5-Standard of nano particles in the air possible, it is nevertheless a step towards the right direction to grasp much more reality than with the PM10-Standard.