Dry Deposition Fluxes and Mass Size Distributions of Pb, Cu, and Zn Measured in Southern Lake Michigan during AEOLOS

Abstract

As part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS) the dry deposition fluxes and atmospheric size distributions (ASDs) of anthropogenic metals were measured over the southern basin of Lake Michigan. The measurements were made during winter, summer, and fall, concurrently, in Chicago, IL; over Lake Michigan onboard the U.S. EPA RV Lake Guardian; and in South Haven, MI. The flux of Pb, Cu, and Zn was substantially higher in Chicago than in either South Haven or over Lake Michigan. The average measured Pb, Cu, and Zn fluxes were 0.07, 0.06, and 0.20 mg m -2 day -1 in Chicago; 0.003, 0.01, and 0.01 mg m -2 day -1 over Lake Michigan; and 0.004, 0.007, and 0.004 mg m -2 day -1 in South Haven. When the wind was from Chicago over the lake, the fluxes and concentrations measured over the lake were higher than when the wind was from other directions. In general, these anthropogenic metals had higher concentrations in the fine particle mode than in the coarse particle mode. Modeled and measured fluxes were in reasonable agreement. Coarse particles were found to be responsible for the majority of the flux at all locations.

Overall elemental dry deposition velocities measured around Lake Michigan

“…Measurements made with a smooth surrogate surface with a sharp leading edge have been shown to agree well with results of modeled dry deposition if complete atmospheric size distributions are used (Holsen and Noll, 1992;Paode et al, 1998;Sofuoglu et al, 1998).…”

“…For none of the elements were r values highest using "ne particle concentrations. This "nding is because the majority of the #ux is due to particles larger than 2.5 m in size due to their high deposition velocities (Davidson and Wu, 1990;Paode et al, 1998;Dulac et al, 1989;Holsen and Noll, 1992) and indicates that best approach to estimate overall dry deposition is by using either coarse or total particle concentrations. Fig.…”

“…Details of sample preparation are described in Paode et al (1998) and the Illinois Institute of Technology, Air Quality Laboratory SOP (US EPA, 1996). Sampling started on December 1993 and concluded in October 1995.…”

“…The strict quality assurance and quality control guidelines developed for analysis of dry deposition samples as part of the LMMB were followed and are described in Paode et al (1998) and Sofuoglu et al (1998). These included development of method detection limits (MDLs), analysis of process and "eld blanks, and measurement of extraction e$ciencies using Urban Particulate Matter (NIST 1643).…”

Dry Deposition Fluxes and Atmospheric Size Distributions of Mass, Al, and Mg Measured in Southern Lake Michigan during AEOLOS

“…Dulac et al (1989 re-2 ported aluminum flux of 0.87 mg/m -day over the western Mediterranean sea. Although spatial flux trends for anthropogenic metals were similar, the magnitude of flux was an order of magnitude lower than for these crustal metals (Paode et al, 1998).…”