Particulate matter aerosols contribute to haze diminishing vistas and scenery at national parks and wilderness areas within the United States. To increase understanding of the sources of carbonaceous aerosols at these settings, the total carbon loading and 14C/C ratio of PM 2.5 aerosols at nine Interagency Monitoring for Protection of Visual Environments (IMPROVE) network sites were measured. Aerosols were collected weekly in the summer and winter at one rural site, two urban sites, five sites located in national parks and one site located in a wildlife preserve. The carbon measurements together with the absence of 14C in fossil carbon materials and known 14C/C levels in contemporary carbon materials were used to derive contemporary and fossil carbon contents of the particulate matter. Contemporary and fossil carbon aerosol loadings varied across the sites and suggest different percentages of carbon source inputs. The urban sites had the highest fossil carbon loadings that comprised around 50% of the total carbon aerosol loading. The wildlife preserve and national park sites together with the rural site had much lower fossil carbon loading components. At these sites, variations in the total carbon aerosol loading were dominated by nonfossil carbon sources. This suggests that reduction of anthropogenic sources of fossil carbon aerosols may result only in little decrease in carbonaceous aerosol loading at many national parks and rural areas. Examination of the major sources of uncertainty that might cause contemporary carbon contents to be artificially high indicates that potential errors and biases in the methodology do not change the fundamental conclusions of this study.