Stable Carbon Isotope Signatures of Carbonaceous Aerosol Endmembers in the Tibetan Plateau.

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 δ13C 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 δ13C 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 13C-depleted relative to fossil fuel-derived aerosols reported in other regions, while biomass fuel-derived aerosols from the TP were 13C-enriched relative to biomass fuel-derived aerosols reported in other regions. The δ13C 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.

Dust dominates glacier darkening across majority of the Tibetan Plateau based on new measurements.

Rapid retreat and darkening of most glaciers in the Tibetan Plateau (TP) are enhanced by the deposition of light-absorbing particles (LAPs). Here, we provided new knowledge on the estimation of albedo reduction caused by black carbon (BC), water-insoluble organic carbon (WIOC), and mineral dust (MD), based on a comprehensive study of snowpit samples from ten glaciers across the TP collected in the spring of 2020. According to the albedo reductions caused by the three LAPs, the TP was divided into three sub-regions: the eastern and northern margins, Himalayas and southeastern TP, and western to inner TP. Our findings indicated that MD had a dominant role in causing snow albedo reductions across the western to inner TP, with comparable effects to WIOC but stronger effects than BC in the Himalayas and southeastern TP. BC played a more important role in the eastern and northern margins of the TP. In conclusion, the findings of this study emphasize not only the important role of MD in glacier darkening across majority of the TP but also the influence of the WIOC in enhancing glacier melting which indicates the dominant contribution of non-BC components in the LAP-related glacier melting of the TP.

Concentrations, sources, fluxes, and absorption properties of carbonaceous matter in a central Tibetan Plateau river basin.

Carbonaceous matter (CM) (such as water-insoluble organic carbon (WIOC), black carbon (BC), and water-soluble organic carbon (WSOC)) has a significant impact on the carbon cycle and radiative forcing (RF) of glacier. Precipitation samples and glacier's snow/ice samples (snowpit, surface snow, and granular ice) (Xiao dongkemadi Glacier) were collected at the Dongkemadi River Basin (DRB) in the central Tibetan Plateau (TP) between May and October 2016 to investigate the characteristics and roles of CM in the TP River Basin. WIOC, BC, and WSOC concentrations in precipitation were relatively higher than that in snowpit, but lower than that in surface snow/ice, with the wet deposition fluxes of 0.10 ± 0.002, 0.04 ± 0.001, and 0.12 ± 0.002 g C m-2 yr-1 at DRB, respectively. The positive matrix factorization model identified four major sources (biomass burning source, secondary precursors, secondary aerosol, and dust source) of CM in precipitation at DRB. Two source areas (South Asia and the interior of TP) contributing to the pollution at DRB were identified using a potential source contribution function model, a concentration-weighted trajectory method, and the back-trajectory model. Moreover, the light-absorption by WSOC in the ultraviolet region was 23.0%, 12.1%, and 3.4% relative to the estimated total light-absorption in precipitation, snowpit, and surface snow/ice, respectively. Optical indices analysis revealed that WSOC in snowpit samples presented higher molecular weight, while presented higher aromatic and higher molecule sizes in surface snow/ice and precipitation samples, respectively. RF by WSOC relative to that of BC was estimated to be 17.6 ± 17.6% for precipitation, 10.9 ± 5.8% for snowpit, and 10.7 ± 11.6% for surface snow/ice, respectively, during the melt season in the central TP River Basin. These results help us understand how CM affects glaciers, and they can be utilized to create policies and recommendations that efficiently reduce emissions.

Long-range transport of atmospheric microplastics deposited onto glacier in southeast Tibetan Plateau.

Micoroplastics (MPs) can be transported through atmospheric circulations, and have caused global attentions due to their potential risk to the environment. In this study, MPs in snowpit samples collected from Demula (DML) glacier in southeast Tibetan Plateau were investigated. The results showed that the average abundance of MPs in snow was 9.55 ± 0.9 items L-1, with dominant shapes of plastic fibers and films. MPs size was dominated by MPs <200 µm, with detected minimum size of 48 µm from the DML glacier. MPs in snowpit indicated seasonal variations, showing relatively higher abundance during the monsoon season than that during the non-monsoon season. The chemical composition of MPs and backward air mass trajectory modeling revealed that MPs in DML snowpit mostly originated from the atmospheric long-range transport, suggesting the glacier in southeast Tibetan Plateau can be a temporal sink of atmospheric MPs. The surface structure of the MPs was rough and adhered to a large amount of mineral dust and metallic particles, revealed that these MPs have undergone severe weathering during transportation and after deposition. Based on the MPs data, multi-year average precipitation, and glacier mass balance of DML glacier, the deposition flux of MPs on DML glacier was estimated to be about 7640 ± 720 to 9550 ± 900 items m-2 yr-1 and the export from melting water was about 5.9 ± 1.3 × 109 to 6.6 ± 1.4 × 109 items yr-1, indicating the glacier may be also an important source of MPs to the downstream ecosystems. These results provided the current status of MPs pollution on the Tibetan Plateau glaciers and new data to the study of MPs in typical cryospheric regions.

Molecular compositions, optical properties, and implications of dissolved brown carbon in snow/ice on the Tibetan Plateau glaciers.

Brown carbon (BrC)/water-soluble organic carbon (WSOC) plays a crucial role in glacier melting. A quantitative evaluation of the light absorption characteristics of WSOC on glacier melting is urgently needed, as the WSOC release from glaciers potentially affects the hydrological cycle, downstream ecological balance, and the global carbon cycle. In this work, the optical properties and composition of WSOC in surface snow/ice on four Tibetan Plateau (TP) glaciers were investigated using a three-dimensional fluorescence spectrometer and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The total light-absorption of WSOC in snow/ice at 250-400 nm (ultraviolet region) and 400-600 nm (visible region) accounted for about 60.42% and 27.17% of the light absorption by the total organics, respectively. Two protein-like substances (PRLIS), one humic-like substance (HULIS), and one undefined species of chromophores in snow/ice on the TP glacier surfaces were identified. The lignins and lipids were the main compounds in the TP glaciers and were presented as CHO and CHNO molecules, while CHNOS molecules were only observed in the southeast TP glacier. The light absorption capacity of WSOC in snow/ice was mainly affected by their oxidizing properties. PRLIS and undefined species were closely linked to microbial sources and the local environment of the glaciers (lignins and lipids), while HULIS was significantly affected by anthropogenic emissions (protein/amino sugars). Radiative forcing (RF)-induced by WSOC relative to black carbon were accounted for about 11.62 ± 12.07% and 8.40 ± 10.37% in surface snow and granular ice, respectively. The RF was estimated to be 1.14 and 6.36 W m-2 in surface snow and granular ice, respectively, during the melt season in the central TP glacier. These findings contribute to our understanding of WSOC's impact on glaciers and could serve as a baseline for WSOC research in cryospheric science.

Photobleaching reduces the contribution of dissolved organic carbon to glacier melting in the Himalayas and the Tibetan Plateau.

Dissolved organic carbon (DOC) makes an important contribution to glacier melting in the Himalayas and the Tibetan Plateau (HTP). Photobleaching can effectively reduce the light absorption ability of DOC, further changing its impact on glacier melting, which is not yet well researched in the HTP. Therefore, snowpit samples from the Bayi, Ganglongjiama (GLJM), Jiemayangzong (JMYZ) and Demula (DML) glaciers were collected to study the influence of photobleaching on the light absorption ability of DOC and its impact on glacier melting. The results showed that the DOC concentration of snowpit samples, which was affected by the melting state and photobleaching, decreased from the northern HTP to the southern HTP. At an early stage of melting, the mass absorption cross-section value at 365 nm (MAC365) values showed a negative correlation with DOC concentrations in the snowpit at the JMYZ and DML glaciers, indicating that colored DOC tended to be concentrated in the snowpit during the melting process. With the aggravation of ablation, some snowpit samples in the GLJM and Bayi glaciers had both low concentrations and MAC365 values of DOC due to the reduced influence of photobleaching on the light absorption ability of DOC. Similarly, two fluorescence components (one protein-like component and one humic-like component) were identified in the extracted DOC at the JMYZ and DML glaciers, while those components were not detected in the GLJM glacier. Based on the sources of fluorescent DOC and five-day backward air mass trajectories, long-distance transport of pollutants from South Asia was an important source of snowpit DOC in the southern HTP. In this study, photobleaching can effectively remove colored and fluorescent DOC from snowpit samples in the HTP, further reducing the radiation forcing and glacier melting caused by DOC.

Significant Influence of Carbonates on Determining Organic Carbon and Black Carbon: A Case Study in Tajikistan, Central Asia.

Carbonates cause large uncertainties in determining the concentrations of organic carbon (OC) and elemental carbon (EC), as well as EC's light absorption characteristics, in arid locations, such as Central Asia. To investigate this influence, a comparison between acid (HCl)-treated and original total suspended particle (TSP) samples was conducted in Dushanbe, Tajikistan. According to the results, the OC and EC concentrations were overestimated by approximately 22.8 ± 33.8 and 32.5 ± 33.5%, with the actual values being 11.9 ± 3.0 and 5.13 ± 2.24 µg m-3, respectively. It was found that carbonates had a larger influence from May to October than during the other months, which was significantly correlated with the amount of TSPs on the filter. Furthermore, the mass absorption cross-section of EC (MACEC) increased from 4.52 ± 1.32 to 6.02 ± 1.49 m2 g-1; this indicated that carbonates can significantly decrease MACEC, thus causing an underestimation of approximately 23.9 ± 16.7%. This is the first study that quantifies the influence of carbonates on the light-absorbing abilities of EC.

Carbonaceous matter in the atmosphere and glaciers of the Himalayas and the Tibetan plateau: An investigative review.

Carbonaceous matter, including organic carbon (OC) and black carbon (BC), is an important climate forcing agent and contributes to glacier retreat in the Himalayas and the Tibetan Plateau (HTP). The HTP - the so-called "Third Pole" - contains the most extensive glacial area outside of the polar regions. Considerable research on carbonaceous matter in the HTP has been conducted, although this research has been challenging due to the complex terrain and strong spatiotemporal heterogeneity of carbonaceous matter in the HTP. A comprehensive investigation of published atmospheric and snow data for HTP carbonaceous matter concentration, deposition and light absorption is presented, including how these factors vary with time and other parameters. Carbonaceous matter concentrations in the atmosphere and glaciers of the HTP are found to be low. Analysis of water-insoluable organic carbon and BC from snowpits reveals that concentrations of OC and BC in the atmosphere and glacier samples in arid regions of the HTP may be overestimated due to contributions from inorganic carbon in mineral dust. Due to the remote nature of the HTP, carbonaceous matter found in the HTP has generally been transported from outside the HTP (e.g., South Asia), although local HTP emissions may also be important at some sites. This review provides essential data and a synthesis of current thinking for studies on atmospheric transport modeling and radiative forcing of carbonaceous matter in the HTP.

Light absorption and fluorescence characteristics of water-soluble organic compounds in carbonaceous particles at a typical remote site in the southeastern Himalayas and Tibetan Plateau.

Carbonaceous particles play an important role in climate change, and an increase in their emission and deposition causes glacier melting in the Himalayas and the Tibetan Plateau (HTP). This implies that studying their basic characteristics is crucial for a better understanding of the climate forcing observed in this area. Thus, we investigated characteristics of carbonaceous particles at a typical remote site of southeastern HTP. Organic carbon and elemental carbon concentrations at this study site were 1.86 ± 0.84 and 0.18 ± 0.09 µg m-3, respectively, which are much lower than those reported for other frequently monitored stations in the same region. Thus, these values reflect the background characteristics of the study site. Additionally, the absorption coefficient per mass (α/ρ) of water-soluble organic carbon (WSOC) at 365 nm was 0.60 ± 0.19 m2 g-1, with the highest and lowest values corresponding to the winter and monsoon seasons, respectively. Multi-dimensional fluorescence analysis showed that the WSOC consisted of approximately 37% and 63% protein and humic-like components, respectively, and the latter was identified as the component that primarily determined the light absorption ability of the WSOC, which also showed a significant relationship with some major ions, including SO2-4, K+, and Ca2+, indicating that combustion activities as well as mineral dust were two important contributors to WSOC at the study site.

A new method for extraction of methanol-soluble brown carbon: Implications for investigation of its light absorption ability.

As an important component of organic carbon (OC), brown carbon (BrC) plays a significant role in radiative forcing in the atmosphere. Water-insoluble OC (WIOC) generally has higher light absorption ability than water-soluble OC (WSOC). The mass absorption cross-section (MAC) of WIOC is normally investigated by dissolving OC in methanol. However, all the current methods have shortcomings due to neglecting the methanol insoluble particulate carbon that is detached from the filter and suspended in methanol extracts, which results in MAC uncertainties of the methanol-soluble BrC and its climate warming estimation. In this study, by investigating typical biomass combustion sourced aerosols from the Tibetan Plateau and ambient aerosols from rural and urban areas in China, we evaluated the light absorption of extractable OC fraction for the existing methods. Moreover, a new method was developed to overcome the methanol insoluble particulate carbon detachment problem to achieve more reliable MAC values. We found that OC can be dissolved in methanol in a short time (e.g., 1 h) and ultrasonic treatment and long-term soaking do not significantly increase the extractable OC fraction. Additionally, we proved that methanol insoluble particulate carbon detachment in methanol does exist in previous methods, causing overestimation of the BrC mass extracted by methanol and thus the underestimation of MAC values. We therefore recommend the newly developed extraction method in this study to be utilized in future related studies to quantitatively obtain the light absorption property of methanol-soluble BrC.

Seasonality of carbonaceous aerosol composition and light absorption properties in Karachi, Pakistan.

Characteristics of carbonaceous aerosol (CA) and its light absorption properties are limited in Karachi, which is one of the most polluted metropolitan cities in South Asia. This study presents a comprehensive measurement of seasonality of CA compositions and mass absorption cross-section (MAC) of elemental carbon (EC) and water-soluble organic carbon (WSOC) in total suspended particles (TSP) collected from February 2015 to March 2017 in the southwest part of Karachi. The average TSP, organic carbon (OC), and EC concentrations were extremely high with values as 391.0 ± 217.0, 37.2 ± 28.0, and 8.53 ± 6.97 µg/m3, respectively. These components showed clear seasonal variations with high concentrations occurring during fall and winter followed by spring and summer. SO42-, NO3-, K+, and NH4+ showed similar variations with CA, implying the significant influence on atmospheric pollutants from anthropogenic activities. Relatively lower OC/EC ratio (4.20 ± 2.50) compared with remote regions further indicates fossil fuel combustion as a primary source of CA. Meanwhile, sea salt and soil dust are important contribution sources for TSP. The average MAC of EC (632 nm) and WSOC (365 nm) were 6.56 ± 2.70 and 0.97 ± 0.37 m2/g, respectively. MACEC is comparable to that in urban areas but lower than that in remote regions, indicating the significant influence of local emissions. MACWSOC showed opposite distribution with EC, further suggesting that OC was significantly affected by local fossil fuel combustion. In addition, dust might be an important factor increasing MACWSOC particularly during spring and summer.

High particulate carbon deposition in Lhasa-a typical city in the Himalayan-Tibetan Plateau due to local contributions.

The Himalayan-Tibetan Plateau is a typical remote region with sparse air pollution. However, air pollution in cites of the inner Himalayan-Tibetan Plateau is relatively serious due to emissions from local residents. Carbonaceous aerosols are not only an important component of air pollutants that affect the health of local residents but also an important trigger of climate change. In this study, the annual wet and dry deposition rates of carbonaceous particles were investigated in Lhasa-a typical city in the Himalayan-Tibetan Plateau, by collecting precipitation and dry deposition samples and analyzing with a thermal-optical measurement protocol. The results showed that the in-situ annual wet deposition rates of water-insoluble organic carbon (WIOC) and black carbon (BC) were 169.6 and 19.4 mg m-2 yr-1, respectively, with the highest and lowest values occurring in the monsoon and non-monsoon periods, respectively. Both precipitation amounts and concentrations of WIOC and BC contributed to wet deposition rates. The dry deposition rates of WIOC and BC in Lhasa had an opposite seasonal variation to that of wet deposition, with annual average deposition rates of 2563.9 and 165.7 mg m-2 yr-1, respectively, which were much higher than those of the nearby glacier region and remote area. These values were also much higher than the results from modeling and empirical calculations, indicating that Lhasa is a high pollution point that cannot capture by models. The results in this study have significant implications for the transport of local emissions in Lhasa to the nearby remote and glacier regions.

[Characteristics and Influencing Factors of Stable Hydrogen and Oxygen Isotopes in Groundwater in the Permafrost Region of the Source Region of the Yangtze River].

We use 84 rainfall samples collected during June to September 2017 from the Dongkemadi basin, source region of the Yangtze River, China, to analyze the characteristics and influencing factors of stable isotopes in groundwater, and further discuss the groundwater recharge sources. The results showed that the range of groundwater δ18 O values in this permafrost region varied from -15.3‰ to -12.5‰ (mean -14.0‰). The range of δD values in groundwater varied from -108.9‰ to -91.7‰ (mean -100.2‰). Compared with local atmospheric precipitation, groundwater isotopes were relatively enriched. The slope and intercept of the groundwater line (GL) in the study area were both lower than of those of the global and local meteoric water lines (GMWL and LMWL), thus indicating that groundwater in the study area was subjected to evaporation during rainfall recharge of groundwater. The d-excess values of groundwater varied from 4.9‰ to 25.0‰ (mean 11.6‰), which was close to the average d-excess value determined for global average rainfall (10‰), but lower than that of rainfall in the study area (15.1‰). The influencing factors on the composition and variation of groundwater isotopes were different in different periods. The permafrost active layer was relatively thin during periods of increasing air temperature, and groundwater isotopes were significantly affected by air temperature. A temperature decrease during the latter part of the sampling period, when the thickness of the permafrost active layer was still increasing, further increased the retention time of infiltrating rainfall in the soil, thereby eventually leading to evaporation that strengthened the enrichment of heavy isotopes in the groundwater. According to the topographic characteristics of the Dongkemadi basin, the isotopic characteristics of the groundwater, and the factors influencing the isotopic composition, we conclude that rainfall was the main source of groundwater recharge. The results of this study provide a scientific basis for studying water cycle processes in the permafrost regions of the source region of the Yangtze River.

Carbonaceous matter in glacier at the headwaters of the Yangtze River: Concentration, sources and fractionation during the melting process.

Carbonaceous matter has an important impact on glacial retreat in the Tibetan Plateau, further affecting the water resource supply. However, the related studies on carbonaceous matter are still scarce in Geladaindong (GLDD) region, the source of the Yangtze River. Therefore, the concentration, source and variations of carbonaceous matter at Ganglongjiama (GLJM) glacier in GLDD region were investigated during the melting period in 2017, which could deepen our understanding on carbonaceous matter contribution to glacier melting. The results showed that dissolved organic carbon (DOC) concentration of snowpit samples (283 ±â€¯200 µg/L) was much lower than that of precipitation samples (624 ±â€¯361 µg/L), indicating that large parts of DOC could be rapidly leached from the snowpit during the melting process. In contrast, refractory black carbon (rBC) concentration measured by Single Particle Soot Photometer of snowpit samples (4.27 ±â€¯3.15 µg/L) was much higher than that of precipitation samples (0.97 ±â€¯0.49 µg/L). Similarly, DOC with high mass absorption cross-section measured at 365 nm value was also likely to enrich in snowpit during the melting process. In addition, it was found that both rBC and DOC with high light-absorbing ability began to leach from the snowpit when melting process became stronger. Therefore, rBC and DOC with high light-absorbing ability exhibited similar behavior during the melting process. Based on relationship among DOC, rBC and K+ in precipitation, the main source of carbonaceous matter in GLJM glacier was biomass burning during the study period.

Black carbon in surface soil of the Himalayas and Tibetan Plateau and its contribution to total black carbon deposition at glacial region.

At present, the glaciers in the Himalayas and the Tibetan Plateau (HTP) are retreating partly due to albedo reduction caused by deposited light-absorbing impurities such as mineral dust (MD) and black carbon (BC). Because BC also exists widely in MD from surface soil, it is necessary to further evaluate the contribution of BC from MD to the total BC at glacier region. This will help to improve the study of BC sources by considering the relative contributions from MD and direct combustion sources. Therefore, in this study, concentrations of total organic carbon (TOC) and fine particles of BC from 43 surface soil samples of the HTP were investigated. The contribution of BC from MD to total BC deposited at the glacier region was evaluated. The results showed strong correlations between TOC and BC of studied samples (R2 = 0.70, p < 0.01), suggesting that they have similar sources and activity characteristics. The average BC concentration of studied samples was 2.02 ± 1.55 mg g-1, much lower than those of particles deposited at the glacier region and other regions with high soil TOC concentration. The contributions of BC from MD to total surface BC at two glaciers of the inner HTP (Zhadang and Xiaodongkemadi) were 17.66 ± 10.84% and 20.70 ± 16.35%, respectively. Therefore, the contribution of MD to glacier melting of the HTP is higher than that of previously assumed after BC coming along with MD is considered. Because MD concentration is higher at north and west part of the HTP, the contributions of MD at these glacier regions should be larger than previously assumed.

[Characteristics of Stable Isotopes in Precipitation and Moisture Sources in the Headwaters of the Yangtze River].

Based on the stable isotopes of 73 precipitation samples continuously collected from May to October 2014 and related meteorological statistics in the Dongkemaldi Basin, the characteristics of δD, δ18O, and d-excess of precipitation, as well as the correlations between δ18O and the rainfall amount and air temperature were analyzed. The moisture sources were tracked by the HYSPLIT model to further estimate the contribution of different water vapor sources to the rainfall amount. The results showed that the range of δ18O and δD values varied from -26.5‰ to 1.9‰ and -195.2‰ to 34.0‰, respectively; meanwhile, the δ18O and δD values in precipitation fluctuated greatly with time in response to water vapor transport from different moisture sources of the Qinghai-Tibet Plateau. The slope and intercept of the Local Meteoric Water Line (LMWL) were both higher than those of the Global Meteoric Water Line (GMWL) and close to the LMWL in the northern area of the Qinghai-Tibet Plateau. The relationship between δ18O and δD in different precipitation types showed significant differences, which were mainly related to the source of water vapor and meteorological conditions during the process of precipitation formation. Because of the influence of local evaporation and the transport process of water vapor, the d-excess values of atmospheric precipitation were relatively large; the δ18O in precipitation had a significant amount effect, but had no temperature effect, thus indicating that the rainfall amount was more effective in controlling the stable isotope content of atmospheric precipitation than temperature. The modeled trajectory of vapor sources showed that water vapor of precipitation was mainly derived from the marine vapor carried by the southwest monsoon, local moisture, and the westerly water vapor, and their contributions to the rainfall amount were 43%, 36%, and 21%, respectively. The results of this study can contribute to further understanding of the atmospheric circulation characteristics and water cycle process of the Dongkemadi basin in the headwaters of the Yangtze River.

[Chemical Characteristics and Ionic Sources of Precipitation in the Source Region of the Yangtze River].

Using 64 precipitation samples collected from June to September 2013 in the Dongkemadi Basin in the source region of the Yangtze River, the pH, conductivity, and main ionic concentration characteristics of precipitation were analyzed. The main ionic sources of precipitation and their relationships with atmospheric circulation were examined using factor analysis, correlation analysis, enrichment factor analysis, and backward trajectory analysis. The results showed that the range of precipitation pH values varied from 5.26 to 9.25 with a weighted average of 6.70, and conductivity ranged from 0.23 to 28.70 µS·cm-1 with a weighted average of 3.45 µS·cm-1. The conductivity of precipitation was lower than for the Mt. Waliguan basin (China Global Atmosphere Watch baseline observatory). The total ionic concentrations in the precipitation ranged from 7.0 to 376.9 µeq·L-1 with a weighted average of 40.8 µeq·L-1. The ranked order of ionic concentrations was HCO3- > NH4+ > Ca2+ > NO3- > SO42- > Na+ > Cl- > K+ > Mg2+. HCO3-, NH4+,Ca2+, and NO3- were the dominant ions, which accounted for 74.75% of the total ionic concentration. Fractional acidity (FA) analysis showed that 97.8% of the precipitation acidity was neutralized by alkaline constituents. Neutral factor (NF) analysis indicated that NH4+ and Ca2+ were the dominant neutralization constituents in the precipitation. The precipitation ions in this study area were mainly derived from terrestrial material, while input from marine sources was relatively low. Backward trajectory analysis revealed that the total ionic concentrations varied significantly between the different sources, which followed the order of local sources>westerly sources>monsoon sources. This indicates that different atmospheric circulation conditions and air mass sources have a significant influence on the chemical composition of precipitation in this area. To some extent, the chemical characteristics of precipitation could reflect the air quality and background values for remote areas due to the limited effect of human activities. The results of this study provide a scientific basis for the protection of water quality and the assessment of the impact of human activities on the atmospheric environment in the source region of the Yangtze River.