In the early 1970s certain filters from the CHESS network were collected and sent to the Human Studies Laboratory (HSL) Bioenvironmental Laboratory Branch (BELB) for sulfate and nitrate analyses. These analyses were interrupted on October 1, 1972 and subsequently continued under contract signed March 1973 with Rickman, Edgerley, Tomlinson, and Associates (RETA). Many of the filters were not analyzed until RETA became fully operational in May 1973, whereupon their measurements began to be inexplicably and consistently low. The disparity between HSL results and RETA's findings engendered an investigation involving reanalyses to verify the apparent disparity, and then to determine a statistical adjustment factor to correct for anomalies. In November 1974 Rockwell International undertook the reanalyses of these CHESS filters. In Rockwell's reanalyses, the difference in RETA's sulfate data showed a mean ratio of 51%, but the results on nitrates were inconclusive. The effects of time and handling were not conclusively determined, although there was an indication that nitrates decompose with timelapse more significantly than sulfates. Based on the results of this report, it was recommended that CHESS measurements for sulfates be increased by 51% for all sites for the entire period RETA performed these analyses.

"EPA-600/1-77-004".