Seasonal and spatial trends of certain chlorobenzene isomers in the Michigan atmosphere

Four isomers of chlorobenzenes (1,2,3,4-tetra-, 1,2,4,5-tetra- (TeCB), penta- (PeCB) and hexa-(HCB)) were analyzed in atmospheric gases collected over 24 h as often as every six days from Pellston, Deckerville, South Haven and Dexter, Michigan during one year. HCB sampling also included 10 earlier months. Sites were located to give broad coverage to Michigan and, in three cases, to measure variations in concentration near one of the Great Lakes where chlorobenzenes are compounds of concern. The TeCB isomers show high concentrations at every site at various times. The ratio between 1,2,3,4- and 1,2,4,5-TeCB isomers is approximately 2 for most sampling dates, including both high and background concentrations. One significant variation occurs statewide because of a higher concentration of 1,2,4,5-TeCB. At the South Haven site PeCB concentrations are much higher than other sites during June and July. One date of extreme PeCB concentration at South Haven corresponds to high levels of both TeCB isomers, suggesting a similar source. HCB concentrations have a greater range of values during warmer seasons, suggesting that there are a variety of sources to Michigan, some of which are affected by seasonal air temperature variations.