PM_2.5 forecasting has become an increasingly important part of air quality public outreach programs designed to inform the public about air quality conditions, protect public health, and encourage the public to reduce activities that contribute to air pollution.

Starting in January 2003, current- and next-day forecasts for PM_2.5 were issued for cities throughout the United States, including a number of cities in the Midwest: Columbus, Cleveland, and Cincinnati, Ohio; Chicago, Illinois; and Detroit, Michigan. Through daily forecasts, it became clear that certain atmospheric phenomena and their impact on PM_2.5 concentrations needed more analysis to better understand the atmospheric mechanics that influence PM_2.5 episodes.

As a result, a case study was performed to examine the influence of atmospheric features on PM_2.5 concentrations for the period September 9 through 15, 2003. At various times during the episode, a number of different atmospheric phenomena impacted regional air quality. These phenomena included atmospheric blocking, frontal dynamics and kinematics, frontolysis, particulate transport, and surface cyclogenesis. An analysis of these phenomena provides air quality forecasters with a better understanding of how complex atmospheric features interact with fine particles and offers suggestions to forecasters for predicting such phenomena.