Impact/Purpose:

1) Develop a TOA protocol that meets the basic assumptions of the method and peer review of the method, 2) understand the role of sampling, analysis, and blank subtraction on the differences between the IMPROVE and STN OC and EC results 3) Evaluate the use of light absorbance methods to estimate EC on human exposure samples, 4) develop a sensitive analytical method suitable for analysis of STN and micro-environmental samples for organic molecular markers, and 5) develop an optimum list of organic molecular markers for source apportionment of particulate matter.

Description:

Carbonaceous material is a major component of ambient PM at all locations in the U.S. and it is composed of two major classes: organic carbon (OC, composed of hundreds of individual compounds) and elemental carbon (EC, also referred to as soot, black carbon, or light adsorbing carbon). Elemental carbon is a major source tracer for diesel emissions, while individual compounds of OC also can be uses as source tracers. Research toward further understanding of the carbonaceous PM, especially with regard to its use for source apportionment and for improving measurement capabilities, will proceed in two parallel efforts: 1) improve understanding of thermal-optical analysis methods now widely used in ambient monitoring networks and 2) develop an optimized list of organic molecular markers for source apportionment applications.

One analytical approach for determining OC and EC on collected filters is by Thermal-Optical Absorption (TOA). The TOA method has a number of published protocols that each provide similar results for total carbon (TC), but varying results for OC and EC based on how OC and EC are determined or split in the analysis. Thus, values of OC and EC are operationally defined and current research by EPA and NIST indicate that the protocols may not meet the basic assumptions underlying this analytical method. Comparison studies between two methods currently employed in our National Air Monitoring Networks, the Speciation Trends Network (STN) and IMPROVE protocols, indicate a 10-20% difference in OC, but up to a factor of 2 (200%) or more in EC, especially in urban environments. Ability to account for these differences with differences in samplers, handling procedures, and blank subtraction methods is variable and location dependent. Thus, integrating the EC and OC results across the two networks for regional analyses (urban measures using STN and rural measures using IMPROVE) is difficult because of the combination of analytical, sampling, and blank subtraction differences. In addition to TOA, indirect methods such as light absorbance are used to estimate EC. These techniques are promising for the analysis of human exposure study samples collected on Teflon filters, however, the relationship between TOA EC and EC estimated from light absorbance on human exposure samples is only moderate. Understanding the sources of variability between the two methods may allow for improving the relationship between the methods.

A more detailed speciation of the organic fraction can be achieved through gas chromatography/mass spectrometery (GCMS) analysis of particulate extracts. An optimized list of organic molecular markers will be developed as a tool for determining source contributions of particulate matter that reduces analytical effort while improving data quality for source apportionment applications. Typically as many as several hundred organic molecular markers have been analyzed for source apportionment applications. A shorter list of compounds would be more convenient for receptor models that require a large number of samples. Factors taken into account in generating the optimum marker list include predictive capability, abundance/detectability, sampling/analytical uncertainty, potential interference, sampling bias, and ease of analysis associated with potential markers. These characteristics will be evaluated for individual candidate markers through data analysis of completed and on-going field studies, and a list of compounds will be generated that maximizes predictive capability while minimizing analytical effort.

Record Details:

Record Type:PROJECT

Start Date:10/01/2004

Projected Completion Date:10/01/2007

OMB Category:Other

Record ID: 114561

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Project Information:

Progress :In FY04, the sampling design for the TOA optimization was completed and samples were collected in Seattle, however, the sampler had to be returned due to noise complaints. The sampler was modified and another sampler purchased to allow for faster collection of samples at a site. Samples have been collected in Atlanta (secondary organics), and will be collected in Los Angeles (motor vehicle) in November 2004 and Seattle (wood smoke) in January 2005. Sample analysis will start as soon as NIST is able to lease a TOA analyzer with the ability to monitor the reflectance and transmittance during the analysis. Joe Conny has published "Optimizing thermal-optical methods for measuring atmospheric elemental (black) carbon: a response surface study" in Aerosol Science Technology and has prepared another "How does thermal-optical analysis for atmospheric elemental carbon behave optically? investigations of the apparent specific absorption cross section."

In FY04, Rutgers initiated IMPROVE and STN sample collection with samplers borrowed from OAQPS. Both Rutgers and Carnegie Mellon are also generating manuscripts that evaluate the current thermal-optical protocols.

In FY04, A manuscript has been submitted by David Olson that describes the comparison of TOA EC and light absorbance "Sampling Artifacts in Measurement of Elemental and Organic Carbon: Low Volume Sampling in Indoor and Outdoor Environments." These samples will be evaluated by additional LAC techniques before the data are provided to Dr. Bond.

In FY04, A high volume injection method has been developed that is suitable for analysis of low volume ambient air and micro-environmental samples such as those available from the STN network and on-going exposure studies. The method will be described in the February AAAR Supersites Specialty Conferences. A manuscript has been submitted by Steve McDow that describes sampling artifact behavior of candidate organic molecular markers.

Relevance :Two important outcomes of this research are improved capabilities for identification of sources responsible for the greatest risk of exposure to particulate matter and determination source control alternatives for implementing national ambient air quality standards for particulate matter.

Resolution of discrepancies associated with OC and EC and development of an optimized list of organic molecular markers will result in two efficient and cost effective tools for determining source contributions of particulate matter from ambient and micro-environmental concentrations by greatly improving our ability to link PM at receptors back to their source. The results may also be useful for epidemiological efforts, understanding atmospheric processes, and effective modeling of PM in air.

Clients :OAQPS, NHEERL, OTAQ, NRMRL, NERL, states, RPO, AMD

Project IDs:

ID Code :20557

Project type :OMIS