Analysis of beta attenuation monitor filter rolls for particulate matter speciation

ABSTRACTInstruments such as Beta Attenuation Monitors (BAMs) provide real-time PM2.5 mass concentration data and are now widely used in compliance monitoring networks. These devices collect the PM on a filter tape in 1-hour samples. In this work, the use of BAM filter spots for chemical speciation was investigated. Filter tapes from several sites in California were analyzed for a series of chemical species including elements, ions, organic and elemental carbon, and molecular markers. A major issue was the blank values in the filter tape. Based on blank spot analyses, it was determined that measurement of organic and elemental carbon (OC/EC) and elements were infeasible. A total of 22 BAM samples (each comprising 24 1-hour spots) from 12 sites were analyzed for ions and black carbon (BC). Additionally, 336 1-hour spots were composited to analyze for molecular markers (MM). Measurements of ions and BC at each site appear to have been underestimated likely due to volatilization losses. MM measurements in these 336 BAM filter spots suggest that organic speciation of BAM filters could be a viable method for measuring useful marker species. Statistical analysis was conducted by grouping samples into classes with mass concentrations greater and less than 80 µg m–3. Measurement of Delta-C concentrations (i.e., Delta C = BC370 nm – BC880 nm) in these two groups of samples revealed that most of the high PM2.5 concentration days PM2.5 greater than 80 µg m–3) were likely not substantially impacted by biomass combustion particles. A major portion of the samples analyzed in this work with high concentrations of PM2.5 were inorganic species such as ammonium sulfate, ammonium nitrate and other ions. Results suggested that some useful information may be derived from BAM tape analyses. However, different filter substrates and sample handling and storage practice might make a wider range of analyses possible.