Relationship Between Large-Scale Atmospheric States, Subsidence,
Static Stability and Ground-Level Ozone in Illinois, USA
Gidon Eshel
and Joseph J. Bernstein
Water, Air and Soil Pollution, Vol. 171, pp. 111-133,
April 2006
Abstract
We analyze ground level ozone pollution in Illinois. We find that
during elevated ground level ozone conditions, Illinois is located
to the south-west of a high pressure system centered over
south-eastern Canada. This state causes weakening of the
climatological westerlies, near-surface southerlies and upper
troposphere northerlies. This results in corresponding weakening of
both lower troposphere heating and upper troposphere cooling by
lateral advective heat flux divergence. Heat balance is restored
primarily by enhanced subsidence, most notably between the surface
and ~400 mb. The strengthened subsidence suppresses boundary
layer deepening by upward surface heat fluxes, resulting in a
shallower than normal boundary layer during times of elevated ground
level ozone. We argue that subsidence induced boundary layer
suppression, aided by elevated temperatures, is the primary cause of
the elevated ground level ozone events. The enhanced subsidence
during those times also dries the lower troposphere, reducing the
probability of moist convection, and thus slowing boundary layer
ventilation.