Todd Lange

The 2003/2004 Libby, Montana PM2.5 Source Apportionment Research Study

Except for areas in California, Libby, Montana is the only designated EPA nonattainment area for fine particulate matter (PM 2.5 ) in the mid and western states. During the winter of 2003/2004, PM 2.5 speciated data (mass, elements, ions, organic/elemental carbon) were collected every six days from November 11, 2003 through February 27, 2004. Using a Chemical Mass Balance computer model (Version 8.0), these data were used to apportion the sources of PM 2.5 in the Libby valley. In support of the source apportionment program, a comprehensive evaluation of the particulate matter associated organic compounds (including polar organics, phenolics, polycyclic aromatic hydrocarbons, and 14 C) present in the airshed was also conducted. CMB modeling results revealed that emissions from residential wood combustion was the major source of PM 2.5 throughout the winter months in Libby, contributing an average of 82% of the measured PM 2.5 . Levoglucosan, a well-known chemical marker for wood smoke, had the highest measured concentrations of any of the 95 polar organic compounds quantified from the fine fraction, accounting for over 15.5% of the measured organic carbon fraction. Other semi-volatile organic compounds with high measured concentrations during the program were four phenolic compounds commonly found in wood smoke, including phenol, 2-methylphenol ( o -cresol), 4-methylphenol ( p -cresol), and 2,4-dimethylphenol. Results from 14 C analysis indicate that as much as 82% of the measured 14 C results from a wood smoke source. These indicators support modeling results that residential wood combustion was the major source of PM 2.5 in Libby, Montana throughout the winter months.

Human (Clovis)–gomphothere (Cuvieronius sp.) association ∼13,390 calibrated yBP in Sonora, Mexico

Significance Archaeological evidence from Sonora, Mexico, indicates that the earliest widespread and recognizable group of hunter-gatherers (“Clovis”) were in place ∼13,390 y ago in southwestern North America. This is the earliest well-documented population on the continent and suggests that the unique Clovis artifact style originated in the southwest or south central part of the continent, well south of the Arctic gateways into the continent. These hunters targeted gomphotheres, an elephant common in south and central North America, but unknown in association with humans or at this late age in North America. The earliest known foragers to populate most of North America south of the glaciers [∼11,500 to ≥ ∼10,800 14C yBP; ∼13,300 to ∼12,800 calibrated (Cal) years] made distinctive “Clovis” artifacts. They are stereotypically characterized as hunters of Pleistocene megamammals (mostly mammoth) who entered the continent via Beringia and an ice-free corridor in Canada. The origins of Clovis technology are unclear, however, with no obvious evidence of a predecessor to the north. Here we present evidence for Clovis hunting and habitation ∼11,550 yBP (∼13,390 Cal years) at “El Fin del Mundo,” an archaeological site in Sonora, northwestern Mexico. The site also includes the first evidence to our knowledge for gomphothere (Cuvieronius sp.) as Clovis prey, otherwise unknown in the North American archaeological record and terminal Pleistocene paleontological record. These data (i) broaden the age and geographic range for Clovis, establishing El Fin del Mundo as one of the oldest and southernmost in situ Clovis sites, supporting the hypothesis that Clovis had its origins well south of the gateways into the continent, and (ii) expand the make-up of the North American megafauna community just before extinction.

Consequences of a Rapid Cellulose Extraction Technique for Oxygen Isotope and Radiocarbon Analyses

We use infrared, radiocarbon, and stable isotope analyses to investigate the purity of cellulose extracted from wood using a rapid processing technique. Replicate laboratory standards processed using the standard Brendel method are not significantly different with respect to delta(18)O from those prepared using traditional techniques, although the process does result in a slight acetylation of the wood samples. Radiocarbon comparisons, however, show significant differences. We conclude that the standard Brendel method is appropriate for developing stable isotope time series for high-resolution isotope dendroclimatology but must be used with caution for precision radiocarbon measurements.

Excursions in the 14C record at A.D. 774–775 in tree rings from Russia and America

The calibration of radiocarbon dates by means of a master calibration curve has been invaluable to Earth, environmental and archeological sciences, but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling. Improved instrumentation has contributed to high-resolution (interannual) radiocarbon activity measurements, which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5–10 years of most of the calibration scale. One such spike has been recently reported from tree rings from Japan and then again in Europe at A.D. 774–775, for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude (northern Siberia) and bristlecone pine from lower latitude (the White Mountains of California). Our results confirm an abrupt ~ 15‰ 14C activity increase from A.D. 774 to 776, the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most likely responsible.

The impact of wood smoke on ambient PM2.5 in northern Rocky Mountain valley communities.

During the winters of 2006/2007 and 2007/2008, PM2.5 source apportionment programs were carried out within five western Montana valley communities. Filter samples were analyzed for mass and chemical composition. Information was utilized in a Chemical Mass Balance (CMB) computer model to apportion the sources of PM2.5. Results showed that wood smoke (likely residential woodstoves) was the major source of PM2.5 in each of the communities, contributing from 56% to 77% of the measured wintertime PM2.5. Results of 14C analyses showed that between 44% and 76% of the measured PM2.5 came from a new carbon (wood smoke) source, confirming the results of the CMB modeling. In summary, the CMB model results, coupled with the 14C results, support that wood smoke is the major contributor to the overall PM2.5 mass in these rural, northern Rocky Mountain airsheds throughout the winter months.

DIRECT MEASUREMENT OF THE SEED BANK AGE STRUCTURE OF A SONORAN DESERT ANNUAL PLANT

We describe a new approach to determining the age structure of seed banks of natural plant populations and apply it to a natural population of the Sonoran Desert winter annual, Pectocarya recurvata (Boraginaceae). Unlike other 14C techniques, tandem accelerator mass spectrometry (TAMS) counts the number of carbon isotope atoms, permitting high precision with small samples. Aboveground nuclear bomb tests caused atmospheric 14C levels to peak in 1963. Their subsequent gradual decline provides a signal for aging seed banks with TAMS. We constructed a calibration curve using seeds with known dates of production during 1980–1995, then used it to age 53 seeds sampled from a natural seed bank in 1993, at the Desert Laboratory in Tucson, Arizona. Seed number declined with age at an approximately exponential rate, with the oldest recovered seed having an estimated age of 5 yr (95% ci = ±2.3 yr). The seed bank age structure was judged more than adequate to buffer this population from typical fluctuations, based on ...

CLIMATE IN THE GREAT LAKES REGION BETWEEN 14,000 AND 4000 YEARS AGO FROM ISOTOPIC COMPOSITION OF CONIFER WOOD

The isotopic composition of ancient wood has the potential to provide information about past environments. We analyzed the δ13C, δ18O, and δ2H of cellulose of conifer trees from several cross-sections at each of 9 sites around the Great Lakes region ranging from ~4000 to 14,000 cal BP. Isotopic values of Picea, Pinus, and Thuja species seem inter- changeable for δ18O and δ2H comparisons, but Thuja appears distinctly different from the other 2 in its δ13C composition. Iso- topic results suggest that the 2 sites of near-Younger Dryas age experienced the coldest conditions, although the Gribben Basin site near the Laurentide ice sheet was relatively dry, whereas the Liverpool site 500 km south was moister. The spatial isotopic variability of 3 of the 4 sites of Two Creeks age shows evidence of an elevation effect, perhaps related to sites farther inland from the Lake Michigan shoreline experiencing warmer daytime growing season temperatures. Thus, despite floristic similarity across sites (wood samples at 7 of the sites being Picea), the isotopes appear to reflect environmental differences that might not be readily evident from a purely floristic interpretation of macrofossil or pollen identification.

Accelerator mass spectrometry at Arizona: geochronology of the climate record and connections with the ocean.

There are many diverse uses of accelerator mass spectrometry (AMS). Carbon-14 studies at our laboratory include much research related to paleoclimate, both with 14C as a tracer of past changes in environmental conditions as observed in corals, marine sediments and many terrestrial records. Terrestrial records such as forest fires can also show the influence of oceanic oscillations, whether they are short-term such as ENSO, or on the millennial time scale. In tracer applications, we have developed the use of 129I as well as 14C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson for several of these fields and hope to give some idea of the breadth of these studies.

Changes in sediment accumulation rate in an oxbow lake following late 19th century clearing of land for agricultural use: A 210Pb, 137Cs, and 14C study in Mississippi, USA

Sediment cores were collected from 2 sites in the forested fringe of an oxbow lake surrounded by land that was converted from forest to agricultural use in the late 19th century. The 2 sampling areas were selected to represent areas of high (West site) and low (east site) current sediment accumulation rates, based on distance from a perennially discharging stream. Modern (post settlement and land clearing) sediment accumulation rates were calculated using (super 210) Pb and (super 137) Cs on bulk sediment samples from 2 cores from each site. Two additional cores were collected from each site for radiocarbon analysis of twig cellulose with the assumption that most twigs in the sediment within the forested fringe fell from overhead and are contemporaneous with the sediment. Only the West site, however, yielded sufficient identifiable twig material for analysis. Modern sediment accumulation rates based on (super 210) P and (super 137) Cs fall between 0.2-0.4 cm/yr at the East site, and 0.7-1.3 cm/yr at the West site (nearest the stream inlet), with approximate agreement between the (super 210) Pb and (super 137) Cs methods. Modern sediment accumulation rate based on bomb-pulse (super 14) C activity of twigs from cores from the West site is approximately 1.0 cm/yr, in agreement with the (super 210) Pb and (super 137) Cs results results. Historic sediment accumulation rates were estimated at the West site using twigs from deeper intervals with pre-bomb 14C activity. Sediment covering approximately 1000 yr of pre-settlement sediment accumulation exhibited evidence of minor bioturbation or in-washing of reworked material, but with a clearly lower accumulation rate of less than 0.1 cm/yr.

Application of accelerator mass spectrometry to environmental and paleoclimate studies at the University of Arizona

Abstract A wide range of climatic, geologic and archaeological records can be characterized by measuring their 14 C and 10 Be concentrations, using accelerator mass spectrometry (AMS). These records are found not only in the traditional sampling sites such as lake sediments and ice cores, but also in diverse natural records. The purpose of this paper is to highlight some selected applications of AMS at the University of Arizona, including sample preparation, applications of AMS radiocarbon dating to learning about climatic changes in the past, modern 14 C studies, and 10 Be and 129 I measurements.