An ozone alert in July of 1974 in the Washington, D.C., area is examined in detail. Ozone data for 16 stations in the Richmond-to-Baltimore corridor are examined in conjunction with meteorological data for the alert period. Emphases are given to trajectories of the air between the surface and 1000 meters and the mixing height and winds aloft data of the air pollution forecasts of the National Weather Service. The investigation revealed: (1) the period with high ozone concentrations was one when synoptic scale stagnation at the surface and aloft prevailed most of the time together with high temperatures and abundant solar radiation; (2) despite overall stagnation over a very large region there were periods when 48-hour trajectories showed that ozone could have been transported from potential source areas as far as 1000 kilometers upwind; (3) that (a) the Richmond-to-Baltimore corridor was at the southern and eastern periphery of a large area in the industrial eastern United States which had high ozone concentrations, and (b) many of the distant potential source areas implicated in the trajectory analyses observed high ozone concentration; and (4) that any abatement strategy for this type of alert, even though associated with stagnation, will have to take into account both local and distant sources.

"February 1978." Includes bibliographical references (p. 13-16). "EPA-600/4-78-016."

An ozone alert in July of 1974 in the Washington, D. C., area is examined in detail. Ozone data for 16 stations in the Baltimore-to-Richmond corridor are examined in conjunction with meteorological data for the alert period. Exphases are given to trajectories of the air between the surface and 1000 meters and the mixing height and winds aloft data of the air pollution forecasts of the National Weather Service. The investigation revealed: (1) the period with high ozone concentrations was one when synoptic scale stagnation at the surface and aloft prevailed most of the time together with high temperatures and abundant solar radiation; (2) despite overall stagnation over a very large region there were periods when 48-hour trajectories showed that ozone could have been transported from potential source areas as far as 1000 kilometers upwind; (3) that a) the Richmond-to-Baltimore corridor was at the southern and eastern periphery of a large area in the industrial eastern United States which had high ozone concentrations, and b) many of the distant potential source areas implicated in the trajectory analyses observed high ozone concentration; and (4) that any abatement strategy for this type of stagnation-ozone alert will have to take into account both local and distant sources.