The potential health effect, induced by exposure to volatile organic compounds (VOCs) in ambient air for long periods, is an important problem. We have investigated a long-term monitoring method for measurement of VOCs in ambient air. Long-term, nonstop sampling periods of 4-weeks, 7-days, and 24-h were evaluated simultaneously, using mass flow controllers set to 0.5, 2.0, and 14 mL/min, respectively. Ambient air was drawn through a multisorbent sampling tube packed with Carbotrap C, Carbotrap B, and Carboxen 1000. Adsorbates were introduced into a GC/MS using a thermal desorption cold trap injector and determined according to the EPA Method TO-14 list. Concentrations of almost all VOCs estimated by the 7-day or 4-week sampling method were approximately equal to the mean value calculated from the 24-h sampling method for each term, except for compounds bearing a vinyl group such as chloroethene, 1,3-butadiene, and styrene. Concentration variations of CFCs, tetrachloromethane, or 1,1,1-trichloroethane were small, but the other VOCs exhibited significant day-to-day fluctuation reflecting socioeconomic activities and the direction of wind. As an example, daily concentrations of benzene in February and March 1999 ranged from 2 to 10 203L蘥/m{sup}3 and 1.5-8.6 μg/m{sup}3, respectively. This wide variation indicates that long-term, nonstop sampling is necessary for measuring accurate average concentrations of VOCs in ambient atmospheres.
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