Field performance of dichotomous sequential PM air samplers

For over one year, the Environmental Protection Commission of Hillsborough County (EPCHC) in Tampa, Florida, operated two dichotomous sequential particulate matter air samplers collocated with a manual Federal Reference Method (FRM) air sampler at a waterfront site on Tampa Bay. The FRM was alternately configured as a PM2.5, then as a PM10 sampler. For the dichotomous sampler measurements, daily 24-h integrated PM2.5 and PM10–2.5 ambient air samples were collected at a total flow rate of 16.7 l min−1. A virtual impactor split the air into flow rates of 1.67 and 15.0 l min−1 onto PM10–2.5 and PM2.5 47-mm diameter PTFE® filters, respectively. Between the two dichotomous air samplers, the average concentration, relative bias and relative precision were 13.3 μg m−3, 0.02% and 5.2% for PM2.5 concentrations (n=282), and 12.3 μg m−3, 3.9% and 7.7% for PM10–2.5 concentrations (n=282). FRM measurements were alternate day 24-h integrated PM2.5 or PM10 ambient air samples collected onto 47-mm diameter PTFE® filters at a flow rate of 16.7 l min−1. Between a dichotomous and a PM2.5 FRM air sampler, the average concentration, relative bias and relative precision were 12.4 μg m−3, −5.6% and 8.2% (n=43); and between a dichotomous and a PM10 FRM air sampler, the average concentration, relative bias and relative precision were 25.7 μg m−3, −4.0% and 5.8% (n=102). The PM2.5 concentration measurement standard errors were 0.95, 0.79 and 1.02 μg m−3; for PM10 the standard errors were 1.06, 1.59, and 1.70 μg m−3 for two dichotomous and one FRM samplers, respectively, which indicate the dichotomous samplers have superior technical merit. These results reveal the potential for the dichotomous sequential air sampler to replace the combination of the PM2.5 and PM10 FRM air samplers, offering the capability of making simultaneous, self-consistent determinations of these particulate matter fractions in a routine ambient monitoring mode.