Spatial variation in ambient benzene concentrations over a city park.

Passive diffusive samplers were used to collect ambient benzene for a one-week sampling period (April 27 to May 4, 2011) at 11 locations throughout a city park in the Tampa, Florida, area. Concentrations were determined through gas chromatography with mass spectrometry. Spatial variability within the park and its contribution to uncertainty in health risk estimates were studied. Measured concentrations ranged from 0.23 to 0.34 microg/m3. The relative percentage differences for samplers collocated with a regulatory reference monitor and with a duplicate were 3% and 14%, respectively. The spatial variability over the park was small with a coefficient of variation of 11%. The concentration variation due to sampler placement contributes less to uncertainty in health risk estimates than the uncertainty associated with the inhalation unit risk parameter (39% versus 170% relative percent differences over the ranges studied). Results suggest that there is a limit to the spatial resolution needed for risk calculations.