- The purpose of this research was to compare four different media that were used to monitor SOC atmospheric concentrations in remote ecosystems. The accumulation of semi-volatile organic compounds, including pesticides, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), was investigated in lichen, 2-year old conifer needles, resin-based passive air sampling devices (PASDs), and snow. In addition, an analytical method for the trace analysis of these SOCs in lichen, conifer needles, and SOCs in PASDs, was developed and validated. To evaluate the preferential accumulation of SOCs in these media, lichen and conifer needles were collected in 2004, PASDs were collected in 2006 after a 1-year exposure period, and snowpack was collected in spring 2003 and 2004 from the same sites in 5 Western U.S. national parks (NPs), including Sequoia NP, Rocky Mtn. NP, Olympic NP, Glacier NP, and Denali NP. Endosulfan sulfate, a degradation product of the pesticide endosulfan, preferentially accumulated in lichen. Hexachlorobenzene (HCB) and fluorene preferentially accumulated in PASDs, and dacthal, chlorpyrifos, dieldrin, acenapthene, and benzo[ghi]perylene preferentially accumulated in snow. Hexachlorocyclohexanes (HCHs) and PCBs did not preferentially accumulate in any one medium. The influence of SOC physical-chemical properties, including air-water partition coefficient (KAW), octanol-air partition coefficient (Log KOA) and the estimated SOC fraction in the particle phase in the atmosphere (Φ), on accumulation in each medium was also investigated. The effect of SOC physical-chemical properties on medium accumulation was evaluated at all sites from which lichen, conifer needles, PASDs, and snow were collected (82, 85, 33, and 30 sites, respectively). These SOC physical-chemical properties significantly influenced the accumulation of dacthal, endosulfans, trans-chlordane, nonachlors, and several PAHs in several of the media. The results from this research indicate that pesticides and PAHs preferentially accumulate in snow. Therefore, snow should be used, if possible, in short-term studies (months) of SOC concentrations in the atmosphere of remote ecosystems during the winter months. However, lichen may be used instead of snow in warmer regions or for studies that require longer exposure periods and/or summer months. If lichen is not present in the ecosystem, conifer needles may be used; however the measurement of particle-phase SOCs may be limited by needle structure and estimated method detection limits (EDLs). Finally, PASDs may be used for studies interested in the concentration of specific gas-phase SOCs with residence times in the atmosphere over 1 year and for a more quantitative estimate of atmospheric concentrations.