PNNL

Abstract

A coupled meteorological and chemical modeling system with a 12-km horizontal grid spacing was used to simulate the evolution of ozone over the Great Lakes region between May and September of 1999 and 2001. Model performance was evaluated using operational surface and upper-air meteorological measurements and surface ozone data. The overall temporal and spatial variations in hourly ozone concentrations and ozone exposure from control simulations agreed reasonably well with the observations at most locations. The simulated ozone exposure was higher during the summer of 1999 than during 2001, similar to the observations. The emission projection simulation that employed the meteorological conditions of 1999 and increased anthropogenic emissions projected for the year 2020 produced increases in ozone exceeding 80 ppb over the lower peninsula of Michigan, the eastern half of the upper peninsula of Michigan, and over Ontario just north of Lake Superior and Lake Huron. Relatively large increases in ozone exceeding 60 ppb were also produced over agricultural regions. Despite the projected increase in anthropogenic emissions for the year 2020, increases in ozone exceeding 60 ppb occurred only over the lake surfaces and in central Michigan when the meteorological conditions of the summer of 2001 were applied. The meteorological conditions during the summer of 2001 were not as favorable for ozone production and did not result in increased ozone. For both summers, increases in anthropogenic emissions projected for the year 2020 decreased ozone exposure in the immediate vicinity of the largest metropolitan areas. The simulated ozone from this study will be used in the near future as input to biological models to assess the response of ozone-sensitive tree species to current and future ozone levels in the Great Lakes region.