Diurnal Variations in Atmospheric Concentrations of Polychlorinated Biphenyls and Endosulfan: Implications for Sampling Protocols

Polychlorinated biphenyls (PCBs) and endosulfan, both semivolatile organic compounds (SOCs), exhibited large diurnal variations in concentration in Bloomington, IN (see Figure 1). Four samples per day were collected serially over a 5-day period in September 1994. For both SOCs, air samples collected in the morning had twice the concentration of samples 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 from 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.