Ozone production in urban plumes transported over water: photochemical model and case studies in the northeastern and midwestern United States

Abstract

Abnormally high concentrations of O3 have been observed in rural locations on the shore of Lake Michigan and on the Atlantic coast in Maine, at a distance of 300 km or more from major anthropogenic sources. We hypothesize that this O3 is associated with transport from major urban centers and with the suppression of vertical mixing as urban plumes are transported over water. A dynamical/photochemical model suggests that a broad region with elevated O3, NOx and volatile organic carbon (VOC) forms as the Chicago plume travels over Lake Michigan, a pattern consistent with observed O3 at surface monitoring sites. Near-total suppression of dry deposition of O3 and NOx over the lake is needed to produce high O3. -from Authors