Carbonaceous aerosols play an important role in radiative forcing in the remote and climate-sensitive Tibetan Plateau (TP). However, the sources of carbonaceous aerosols to the TP remain poorly defined, in part due to the lack of regionally relevant data about the sources of carbonaceous aerosols. To address this knowledge gap, we present the first comprehensive analysis of the delta C-13 signatures of carbonaceous aerosol endmembers local to the TP, encompassing total carbon, water-insoluble particle carbon, and elemental carbon originating from fossil fuel combustion, biomass combustion, and topsoil. The delta C-13 signatures of these local carbonaceous endmembers differ from components collected in other regions of the world. For instance, fossil fuel-derived aerosols from the TP were C-13-depleted relative to fossil fuel-derived aerosols reported in other regions, while biomass fuel-derived aerosols from the TP were C-13-enriched relative to biomass fuel-derived aerosols reported in other regions. The delta C-13 values of fine-particle topsoil in the TP were related to regional variations in vegetation type. These findings enhance our understanding of the unique features of carbonaceous aerosols in the TP and aid in accurate source apportionment and environmental assessments of carbonaceous aerosols in this climate-sensitive region.

Carbonaceous aerosols play an important role in radiative forcing in the remote and climate-sensitive Tibetan Plateau (TP). However, the sources of carbonaceous aerosols to the TP remain poorly defined, in part due to the lack of regionally relevant data about the sources of carbonaceous aerosols. To address this knowledge gap, we present the first comprehensive analysis of the delta C-13 signatures of carbonaceous aerosol endmembers local to the TP, encompassing total carbon, water-insoluble particle carbon, and elemental carbon originating from fossil fuel combustion, biomass combustion, and topsoil. The delta C-13 signatures of these local carbonaceous endmembers differ from components collected in other regions of the world. For instance, fossil fuel-derived aerosols from the TP were C-13-depleted relative to fossil fuel-derived aerosols reported in other regions, while biomass fuel-derived aerosols from the TP were C-13-enriched relative to biomass fuel-derived aerosols reported in other regions. The delta C-13 values of fine-particle topsoil in the TP were related to regional variations in vegetation type. These findings enhance our understanding of the unique features of carbonaceous aerosols in the TP and aid in accurate source apportionment and environmental assessments of carbonaceous aerosols in this climate-sensitive region.

The influence of the Indian summer monsoon (ISM) and mid-latitude westerlies on the central Tibetan Plateau (TP) during the Holocene, particularly during the mid-Holocene, is still unclear, limiting our understanding of past climate change in this region. Cuona Lake, located on the central TP, is a transitional zone of atmospheric circulation that is well situated for investigations on the interplay between the ISM and mid-latitude westerlies. In this study, multiple proxies of lacustrine sediments from Cuona Lake were measured, including total organic carbon (TOC), total nitrogen (TN), delta C-13(org), n-alkanes, and their hydrogen isotopes, to reconstruct the evolution of climate on the central TP over the past 13 cal kyr BP. Decreased TOC/TN ratios, dominant short-chain n-alkanes/alkanoic acid C-15/16/17, and lower values of n-alkane indicator ratios (carbon preference index and average chain length) throughout the investigated period suggest that the organic matter of the lake essentially originated from aquatic algae, and was weakly affected by terrestrial input. The historic variations in the delta D, TOC, and delta C-13(org) values revealed cold-wet conditions during 12.4-11.4 cal kyr BP, warm-wettest environments during the early Holocene (from 11.4 to 8.2 cal kyr BP), cool-wet conditions in the mid-late Holocene (from 5 to 3 cal kyr BP), and warm-dry conditions since 3 cal kyr BP. The reconstructed climatic variability in the Cuona area agrees well with previous indexes in south-central TP, indicating that the climatic pattern of the studied area is basically controlled by the monsoonal circulation from the late part of the last deglaciation to the early Holocene, with the ISM reaching the north-central TP at similar to 11 cal kyr BP. During the mid-late Holocene, the humid conditions coincided with an enhanced influence of westerlies, providing strong evidence for the contribution of westerlies-delivered moisture to the central TP. Based on a comparison of paleoclimate records, the Cuona region displays a transitional phase between monsoon circulation and westerly jets during the Holocene.

Rising atmospheric carbon dioxide (CO2) may enhance tree growth and mitigate drought impacts through CO2 fertilization. However, multiple studies globally have found that rising CO2 has not translated into greater tree growth despite increases in intrinsic water-use efficiency (iWUE). The underlying mechanism discriminating between these two general responses to CO2 fertilization remains unclear. We used two species with contrasting stomatal regulation, the relatively anisohydric Qilian juniper (Sabina przewalskii) and the relatively isohydric Qinghai spruce (Picea crassifolia), to investigate the long-term tree growth and iWUE responses to climate change and elevated CO2 using tree ring widths and the associated cellulose stable carbon isotope ratios (delta C-13). We observed a contrasting growth trend of juniper and spruce with juniper growth increasing while the spruce growth declined. The iWUE of both species increased significantly and with similar amplitude throughout the trees' lifespan, though the relatively anisohydric juniper had higher iWUE than the relatively isohydric spruce throughout the period. Additionally, with rising CO2, the anisohydric juniper became less sensitive to drought, while the relatively isohydric spruce became more sensitive to drought. We hypothesized that rising CO2 benefits relatively anisohydric species more than relatively isohydric species due to greater opportunity to acquire carbon through photosynthesis despite warming and droughts. Our findings suggest the CO2 fertilization effect depends on the isohydric degree, which could be considered in future terrestrial ecosystem models.

Thermal-optical fractions of organic carbon (OC), elemental carbon (EC), delta C-13 and optical properties of PM(2.5 )from Vehicular Fuel Emissions (VFEs) and Biomass Mixed Fuel Emissions (BMFEs) in India were examined. Heterogeneities in these species across Bharat Stage (BS) emission standards, vehicle type and cooking processes were also captured. Results suggest that distributions of OC and EC sub-fractions and Mass Absorption Efficiency (MAE) are driven by the fuel type, operating, combustion conditions, and emissions control strategies. Variability in thermal-optical fractions of carbon was useful not only in delineating VFEs and BMFEs but also in differentiating compositionally similar sources like gasoline and diesel. The mean delta C-13 value for diesel exhaust (- 26.3 +/- 1.3 parts per thousand) was marginally higher than the value (-27.0 +/- 1.2 parts per thousand) for gasoline and BMFEs. The Brown Carbon (BrC) content in VFEs was <10% while it constituted similar to 60% of the BMFEs. The MAE of both EC and OC of all the sources were calculated at 7 wavelengths (405 nm, 445, 532, 632, 780,808, and 980 nm) and heterogeneity was observed across vehicle types (higher MAEs for MUVs), fuel type (lowest MAEoc values for gasoline-powered vehicles) and BS divisions (BSII category vehicles shown highest MAEs) along with light absorption by OC and EC emitted by these sources. The results of this study characterizing the chemical, optical and isotopic signatures of PM2.5 from three major combustion sources will be useful in enhancing source identification and resolution in source apportionment efforts and in radiative forcing calculations.