(1)Desert Research Institute, Division of Atmospheric Sciences, 2215 Raggio Pkwy, Reno, NV 89512

(2)EPRI, Palo Alto, CA.

Organic carbon mass (OCM) contributes significantly to fine particle mass (PM2.5) which could be related to health, climate and visibility. Concentrations of organic carbon (OC) measured by Thermal Optical Reflectance (TOR) is routinely multiplied by factor of 1.4 to obtain the organic carbon mass. The ratio 1.4 is expected to be higher at the remote sites due to photo-oxidation of the primary emissions during transport.

Samples were collected from five national park sites within the IMPROVE Network (Interagency Monitoring of Protected Visual Environment). Composite seasonal samples from the five sites, namely: Acadia (ACAD), ME; Great Smokey Mountains (GRSM) TN; Big Bend (BIBE), TX; Indian Gardens (INGA) Grand Canyon, AZ; Mount Rainier (MORA), WA were selected from the period 1998-2000. Samples were extracted using dichloromethane (DCM), acetone and water, and then each seasonal extract was deposited individually on a pre-fired, pre-weighed quartz filter punch. Dried punches were then re-weighed to determine the mass (OCM) of the residue and then subjected to TOR analysis to measure OC. Cf, the ratio of OCM/OC, for the weighted DCM and acetone fractions was found to differ from site to site. The lowest and the highest ratios were found at INGA (1.58±0.13) and MORA (2.58±0.29) respectively. The ratio when including all sites is 1.92±0.40, higher than the more commonly used ratio 1.4.