DIURNAL-VARIATIONS IN ATMOSPHERIC CONCENTRATIONS OF POLYCHLORINATED-BIPHENYLS AND ENDOSULFAN - IMPLICATIONS FOR SAMPLING PROTOCOLS

Polychlorinated biphenyls (PCBs) and endosulfan, both semivolatile org anic compounds (SOCs), exhibited large diurnal variations in concentra tion in Bloomington, IN (see Figure 1). Four samples per day were coll ected serially over a 5-day period in September 1994. For both SOCs, a ir samples collected in the morning had twice the concentration of sam ples collected at midnight. The diurnal variations tracked atmospheric temperature, with the highest concentrations recorded at the highest temperatures. An important implication for sampling SOCs is evident fr om this study. If one is attempting to measure the daily concentration of an SOC, sampling should be in multiples of 24 h; sampling for more or less time could lead to inaccurate results.