LaPorte Ground Site Measurements

Statement of Work

Measurements of the Contribution of Semivolatile Particulate Matter to Ambient Suspended Fine Particle Mass

Alexandr Polissar, Box 5810, Department of Chemistry, Clarkson University, Potsdam, NY 13699-5810.
Phone (315) 268-7602, Fax (315) 268-6610. Email polissar@clarkson.edu

Phil Hopke, Clarkson University

The overall goal of this project is to systematically determine the amounts and proportions of semivolatile particulate matter that are not measured by the Federal Reference Method (FRM) for PM_2.5. Current PM_2.5 measurements made according to the FRM are believed to underestimate the total suspended PM concentration due to loss of semivolatile PM (primarily ammonium nitrate and certain organic species) from the filter during sampling, transport, storage and equilibration. The amount of underestimation is probably variable and thus reduces the strength, significance and reliability of statistical relationships between exposure and health outcomes and may also reduce the accuracy of risk assessment for PM related health effects.

This research will help to determine the amount of this underestimation by directly measuring the amount of PM lost during mass measurements made according to the FRM, and it will provide an impartial evaluation of the new sampling methods that have been developed with EPA support.

Two new sampling systems, Continuous Ambient Mass Monitor (CAMM) and Real-time total Ambient Mass Sampler (RAMS), have been developed to better collect the total amount of particulate species in the air and thereby better reflect the actual particulate matter (PM) mass. The CAMM, developed by the Harvard School of Public Health, estimates mass based on the increase in pressure drop across the filter as the load of particles on the filter increases. A mass measurement can be obtained in 20 minutes using low flow rates. After each 20 minutes measurement the filter tape is moved to a new position. Since the concentration of semivolatile components does not change appreciably over 20 minutes, loses due to changes in concentration are minimized. The air stream is dehumidified prior to collection of particles in order to remove particle bound water.

The RAMS, developed by Brigham Young University, uses a carbon impregnated glass fiber filter to absorb any ammonia or nitric acid that evaporates from ammonium nitrate and any organic compounds that evaporate from semivolatile organic PM. Any gas-phase ammonia, nitric acid , or organic compounds that would be absorbed by the filter are removed by a system of denuders preceding the filter. The absorptive filter technique can be used on a TEOM to provide continuous measurements or with a batch sampler for subsequent measurement of mass or composition.

Specific objectives of the project include measuring total suspended fine particle mass concurrently with two newt particle samplers under various conditions and to compare the resulting mass measurements between the two new samplers and other means of airborne particle measurements including a 30C TEOM with an initial PermaPure Dryer, a new type of beta gauge, and nephelometers.

We expect to determine the relative performance of these two new samplers and their measured values as compared to the FRM measured PM2.5 mass. Since there is no way to determine the absolute value of the condensed phase mass, this project can only examine precision and cannot fully assess accuracy of the measurements. We will also determine if we can develop local predictive calibration models that would permit realistic estimates of the total measurable mass from the measurements provided by standard methods like the FRM in conjunction with other measurements as mentioned above.