Laboratory and field evaluation of measurement methods for one-hour exposures to O-3, PM2.5, and CO

While researchers have linked acute (less than 12-hr) ambient O-3, PM2.5, a nd CO concentrations to a variety of adverse health effects, few studies ha ve characterized short-term exposures to these air pollutants, in part due to the lack of sensitive, accurate, and precise sampling technologies. In t his paper, we present results from the laboratory and field evaluation of s everal new (or modified) samplers used in the "roll-around" system (RAS), w hich was developed to measure 1-hr O-3, PM2.5, and CO exposures simultaneou sly. All the field evaluation data were collected during two sampling seaso ns: the summer of 1998 and the winter of 1999. To measure 1-hr O-3 exposures, a new active O-3 sampler was developed that uses two nitrite-coated filters to measure O-3 concentrations. Laboratory c hamber tests found that the active O-3 sampler performed extremely well, wi th a collection efficiency of 0.96 that did not vary with temperature or re lative humidity (RH). In field collocation comparisons with a reference UV photometric monitor, the active O-3 sampler had an effective collection eff iciency ranging between 0.92 and 0.96 and a precision for 1-hr measurements ranging between 4 and 6 parts per billion (ppb). The limits of detection ( LOD) of this method were 9 ppb-hr for the chamber tests and similar to 16 p pb-hr for the field comparison tests. PM2.5 and CO concentrations were measured using modified continuous monitor s-the DustTrak and the Langan, respectively. A size-selective inlet and a N afion dryer were placed upstream of the DustTrak inlet to remove particles with aerodynamic diameters greater than 2.5 mum and to dry particles prior to the measurements, respectively. During the field validation tests, the D ustTrak consistently reported higher PM2.5 concentrations than those obtain ed by the collocated 12-hr PM2.5 PEM samples, by approximately a factor of 2. After the DustTrak response was corrected (correction factor of 2.07 in the summer and 2.02 in the winter), measurements obtained using these metho ds agreed well with R-2 values of 0.87 in the summer and 0.81 in the winter . The results showed that the DustTrak can be used along with integrated me asurements to measure the temporal and spatial variation in PM2.5 exposures . Finally, during the field validation tests, CO concentrations measured us ing the Langan were strongly correlated with those obtained using the refer ence method when the CO levels were above the LOD of the instrument [simila r to1 part per million (ppm)].