Abstract
Flow mechanism causing nighttime smog was investigated by analyzing 1) continuous records of meteorological data and concentration of Oxidants (Ox) for 15 days and 2) aircraft data along the transportation route of a polluted air mass.
It was found that an air mass which passed over the large emission sources along the coastline was transported inland as a sea breeze in the form of a gravity current. A high concentration layer was created in the upper part of the gravity current. It descended at the rear edge of a gravity-current head due to the internal circulation within the head, thus yielding the highest concentration of Ox near the ground there.
