Evaluation and Minimization of Organic Aerosol Sampling Artifacts Using Impactors and Quartz Fiber Filter DenudersEPA Grant Number: R831087
Title: Evaluation and Minimization of Organic Aerosol Sampling Artifacts Using Impactors and Quartz Fiber Filter Denuders
Investigators: Fitz, Dennis R.
Institution: University of California - Riverside
EPA Project Officer: Chung, Serena
Project Period: October 1, 2003 through October 31, 2007
Project Amount: $187,030
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter
Particulate matter (PM) differs from other criteria pollutants in that it consists of a complex chemical mixture. Particulate organic carbon (POC) is a major contributor to PM and consists of thousands of individual compounds covering a full range of chemical and physical characteristics. Many POC constituents are found in significant fractions in both the gas and particulate phases. The amount in each phase depends largely on volatility and polarity. When PM is collected on a fiber filter, POC may volatilize once collected, or gaseous components may adsorb to either the filtration medium or previously collected particulate matter and therefore become apparent POC. These processes, known as collection artifacts, therefore, may cause positive or negative measurement biases compared with the actual concentration found in the air at the time of collection. The objective of this proposed research is to characterize the magnitude of these collection artifacts to assess the contribution and sources of POC to PM2.5, and to devise a practical method of minimizing these artifacts based on diffusion denuding and impaction.
The most appropriate method to minimize collection artifacts uses a denuder to remove gas phase interfering species and then samples with a medium capable of quantitatively capturing the particulate phase. The denuder must be capable of removing hundreds of different potentially interfering species while the collection medium must be able to effectively trap as many. This project will evaluate, under ambient sampling conditions, the best methods to evaluate and minimize the POC collection artifact. The approach is to simultaneously collect POC using nine sampling configurations and compare the results with the PM2.5 Federal Reference Method. The methods are (1) a quartz filter (2) a Teflon-quartz filter pack, (3) a quartz fiber denuder followed by a quartz-quartz filter pack, (4) an impactor to remove particles greater than 0.05µm diameter followed by a quartz-quartz filter pack, (5) an impactor preceded by a quartz fiber denuder and followed by a quartz-quartz filter pack, (6) an impactor followed by a quartz fiber denuder and quartz-quartz filter pack, (7) an impactor preceded by a Teflon filter and followed with a quartz filter, (8) a quartz-quartz filter pack preceded with a carbon-based parallel plate denuder and followed with a carbon-impregnated glass fiber filter, and (9) a quartz-quartz filter pack preceded with a carbon-based denuder and Teflon filter and followed with a carbon-impregnated glass fiber filter. A limited number of samples using configurations 3 and 5 will also be collected to determine the effect of sampling interval and temperature-controlled collection. The capacity of the quartz fiber filter denuder will be evaluated. Collection media will be analyzed for organic and elemental carbon using a thermal volatilization-oxidation approach.
POC is a major component of PM2.5, a criteria pollutant that must be routinely measured to assess health risks. Due to its semi-volatile nature there is a good deal of uncertainty in its contribution to PM2.5. This project will address the uncertainties due to measurement artifacts caused by the collection of particulate organic carbon (POC), which affects both the accuracy of the PM2.5 reference method and the use of POC measurements to assign sources. A practical approach for minimizing artifacts for routine PM2.5 sampling will be developed.