Charcoal records of past fires are important for reconstruction of palaeoenvironments and palaeoclimate, particularly when compared with pollen records of past vegetation, but such records are scarce in the southeastern US. To address the question of how fire activity changed from the Last Glacial Maximum (LGM) into the Holocene as vegetation changed, we chose a site in central Tennessee for which a pollen record exists back to 23,000 cal yr BP. We developed a new microscopic charcoal record based on point counting of microscopic charcoal fragments on pollen slides from Anderson Pond studied by Hazel Delcourt ( 1979 Delcourt HR. 1979. Late Quaternary vegetation history of the Eastern Highland Rim and adjacent Cumberland Plateau of Tennessee. Ecological Monographs 49:255–280. [Crossref], [Web of Science ®] , [Google Scholar] ). The record we produced spans the interval from the LGM to recent and is directly tied to the original pollen record. Charcoal:pollen ratios and charcoal area concentrations are high during the late glacial and track the coniferous pollen record from the LGM to the late glacial, at which point spruce and jack pine pollen markedly diminished along with fire activity. From around 15,000 cal yr BP to the beginning of the middle Holocene, charcoal indices are low. High fire activity began around 8200 cal yr BP, and remained high from ca. 8200–5000 cal yr BP, an interval broadly corresponding to the Mid-Holocene Warm Period (MHWP). The evidence of higher fire activity during the MHWP is coincident with increased percentages of indeterminate pollen grains that are interpreted to signal drier conditions. Charcoal area concentrations declined following the MHWP. Viewed against the original pollen record, the patterns in microscopic charcoal abundance from the LGM to recent at Anderson Pond argue for the strong influence of vegetation as well as climate in driving fire occurrence in eastern temperate North America.

Thin-section (micromorphological) analysis of samples from the upper 1.5 m of a core obtained in 2007 from Anderson Pond, Tennessee, reveals a coherent but discontinuous record of late Pleistocene and Holocene climate change that supports some interpretations from previous pollen and charcoal analyses but indicates a revised Holocene chronology for this classic pollen site. Legacy sediments recording anthropogenic disturbance compose the upper 65 cm of the core (<160 cal yr BP) and are characterized by mixed, darker-colored, and coarser-grained deposits containing reworked soil aggregates, which sharply overlie finer-grained and lighter-colored, rooted middle Holocene sediments interpreted as a paleosol. These mid-Holocene sediments (95–65 cm; 7100–5600 cal yr BP) record extensive warm-dry subaerial soil conditions during the middle Holocene thermal maximum, manifested by illuviated clay lining root pores, and also contain abundant charcoal. Late Pleistocene sediments (150–95 cm), dark-colored and organic-rich, record open-water conditions and include siliceous aggregate grains at 143–116 cm (14,300–13,900 cal yr BP), recording intense fires. Thin sections are not commonly used in studies of paleoclimate from Quaternary lacustrine sediments, but we advocate for their inclusion in multianalytical approaches because they enhance resolution of depositional and pedogenic processes.

In the thermal aging of nitroplasticizer (NP), the produced nitrous acid (HONO) can decompose into reactive nitro-oxide species and nitric acid (HNO3). These volatile species are prone to cause cascaded deterioration of NP and give rise to various acidic constituents. To gain insight on the early stage of NP degradation, an adequate method for measuring changes in the concentrations of HONO, HNO3, and related acidic species is imperative. The typical assessment of acidity in nonaqueous solutions (i.e., acid number) cannot differentiate acidic species and thus presents difficulty in the measurement of HONO and HNO3 at a micromolar concentration level. Using liquid–liquid extraction and ion chromatography (IC), we developed a fast and unambiguous analytical method to accurately determine the concentration of HONO, HNO3, acetic/formic acids, and oxalic acid in aged NP samples. Given by the overlay analysis results of liquid chromatography coupled with quadrupole time-of-flight mass spectrometry and IC, the prominent increase of produced HONO after the depletion of antioxidants is the primary cause of HNO3 formation in the late stage of NP degradation, which results in the acid-catalyzed hydrolysis of NP into 2,2-dinitropropanol and acetic/formic acids. Our study has demonstrated that the aging temperature plays a crucial role in accelerating the formation and decomposition of HONO, which consequently increases the acidity of aged NP samples and hence accelerates the hydrolyzation of NP. Therefore, to prevent NP from undergoing rapid degradation, we suggest that the concentration of HNO3 should be maintained below 1.35 mM and the temperature under 38 °C.