monthly air samples were collected from Saginaw Bay, Sault Ste. Marie (SSM), and Traverse City, MI, to identify spatial and temporal variation in organochlorine (OC) vapors in the central and upper Great Lakes region. Average annual and maximum concentrations of ∑PCB were highest at Traverse and lowest at SSM. PCB 8+5 dominated the congener mix, except at Traverse in the summer. Maxima of HCB, R-and γ-HCH, DDT, and DDE were observed at Traverse or Saginaw, except one unusual event at SSM in May. All compound concentrations varied seasonally at all sites except R-HCH. Correlations measuring regression strength between air temperature and OC concentrations show Saginaw affected most by local sources, and SSM affected the least. Among compounds with high vapor pressure, correlations were low at Traverse indicating nonlocal sources. The spatial and temporal differences observed may limit prediction of regional atmospheric trends of these compounds.

No abstract

[1] Michigan was among the top three apple producing states in the United States from the 1940s to 1969 when DDT was heavily used on its fruit orchards. More than 2 decades after Michigan banned DDT use in 1969, we collected air samples from four sites around the state to measure concentrations of six DDT-related compounds in the atmosphere. At South Haven, an apple producing area, average gas phase concentrations of DDT and DDE compounds were at least 10 times greater than the other sites including Pellston in the north, Deckerville in the east, and Dexter in south-central. Concentrations at South Haven showed a very strong seasonal cycle, an effect of higher air temperatures on moving these residues into the gas phase from a local source. We calculated DH values for all six compounds from the South Haven data which showed that p,p 0 -DDE was the highest at 108 kJ mol À1 . The DH values for all compounds at South Haven had a high correlation with Henry's Law Constant (HLC) (r = 0.7), verifying that HLC is a good indicator of tendency for compound conversion to the gas phase. South Haven was the only site with significant atmospheric particle-associated DDT. Particle/gas ratios there for p,p 0 -DDT and p,p 0 -DDE also had a predictable seasonal variation. Overall, these results show that agricultural sites with similar DDT use history will be continuous sources of atmospheric DDT for decades after application.