Based on the ambient air quality monitoring data of 7 cities in Tibet from 2017 to 2023, the spatial and temporal distribution characteristics of PM₁₀ and PM_2.5 in ambient air in Tibet were analyzed by correlation analysis and GIS Kriging interpolation. The results showed that in Tibet region, the days with PM₁₀ and PM_2.5 as the primary pollutants were characterized by good ambient air quality, mainly concentrated in January–March and October–December. The variation trend of PM₁₀ and PM_2.5 concentration was consistent. The average annual concentration in the whole region reached the first-level standard and showed a downward trend, and the seasonal average concentration showed the characteristics of winter>spring>autumn>summer. The average monthly concentration began to decrease from May, reaching the lowest in August and the highest in December. The hourly concentration showed bimodal characteristics, and the peak appeared from 09:00 to 12:00 in the morning and from 21:00 to 01:00 in the next day. The concentrations of PM₁₀ and PM_2.5 in Nyingchi City in southeastern Tibet were significantly lower than those in other cities, while the concentrations of PM₁₀ and PM_2.5 in Nagqu City in northern Tibet were significantly higher than those in other cities. According to the analysis of Sugimoto model, in the exceedance days with particulate matter as the primary pollutant, dust weather had a particularly significant impact on the concentration of PM₁₀ in the atmospheric environment of Tibet, the average content of dust components in PM₁₀ was 87.9%. 

To investigate the causes and sources of atmospheric fine particulate matter (PM_2.5) pollution in the core area of the Ili River Valley in winter, environmental air particles were collected at 6 sampling sites in the core area, including Yining City and its surrounding counties from December 27, 2021 to January 12, 2022. A total of 58 components, including inorganic elements, water-soluble ions, and carbon components, were analyzed, and positive matrix factorization (PMF) was employed for source apportionment. The results showed that the mean concentration of PM_2.5 during the sampling period was 83±35 μg/m³. Three monitoring sites in Yining City showed the highest pollution levels, followed by Huocheng County. The concentration of SO₄²⁻ in PM_2.5 was the highest (14.1 μg/m³), followed by NO₃⁻ (10.5 μg/m³), NH₄⁺ (8.2 μg/m³), and Cl⁻ (1.6 μg/m³), indicating that coal combustion contributed significantly to pollution in winter. The concentrations of SO₄²⁻ (16.5 μg/m³), NO₃⁻ (11.8 μg/m³), and NH₄⁺ (9.5 μg/m³) reported by Yining City's Ecological Environment Bureau were significantly higher than those at other sites. Sulfur oxidation rate (SOR) and nitrogen oxidation rate (NOR) during air pollution were significantly higher than those in clean days, indicating a strong secondary transformation process. The source apportionment results showed that secondary particles had the highest contribution rate (40%), followed by biomass burning (24%), dust sources (14%), coal combustion (11%), industrial sources (6%), and vehicle sources (4%). Compared to clean days, the contribution rate of secondary particles significantly increased during air pollution, with a 27% increase in the contribution rate, mainly due to the accumulation of precursor concentrations in polluted weather conditions and the favorable conditions for the formation of secondary particles in high humidity. The contribution rate of secondary particles to PM_2.5 in the core area of the Ili River Valley was slightly higher than that in other Chinese cities. The contribution rate of biomass burning sources was higher. Therefore, local control measures are needed to strengthen regulation of local coal combustion, vehicle sources, and biomass burning sources.

To evaluate the contribution of soil wind erosion to the particulate matter emissions of oasis cities, based on collected activity levels and emission factors related to soil fugitive dust, a 3 km×3 km-gridded emission inventory of PM_2.5 and PM₁₀ from soil fugitive dust in Xinjiang typical oasis cities (Altay City, Yizhou District of Hami City, and Kashgar City) in 2021 was developed in combination with Emission Factors and GIS technology. The results showed that the total emissions of PM₁₀ from soil fugitive dust in Altay City, Kashgar City, and Yizhou District of Hami City were estimated to be 40983.79, 6541.97, and 1974362.24 t, respectively. The total emissions of PM_2.5 were estimated to be 7069.69, 1090.49, and 326187.68 t, respectively. The particulate matter emission of Yizhou District of Hami City was the highest among the study areas, and the emission of PM₁₀ is 302 times and 48 times higher than that of Kashgar and Altay. Due to factors such as soil type, location in the sand source area, and high wind speed, the emission intensity of particulate matter from soil wind erosion in Yizhou District of Hami City was also significantly higher than that of the other two cities. The temporal distribution characteristics in Yizhou District of Hami City showed a unimodal pattern, with the highest occurring in May. Kashgar City and Altay City both showed a bimodal pattern, with Kashgar City’s peaks occurring in June and August, and Altay City’s peaks occurring in May and July. 

Continuous measurements of 116 volatile organic compounds (VOCs) species by online gas chromato-graphy-mass spectrometry (GC-MS) from autumn 2023 to summer 2024 in Urumqi and Karamay were used to investigates the pollution characteristics of VOCs, the potential contribution to secondary pollutants, and their sources. The results showed that the average VOC concentration in Urumqi ((31.08±20.7)×10⁻⁹) was higher than in Karamay ((23.08±20.9)×10⁻⁹). Both cities showed a seasonal variation trend with lower VOCs concentrations in spring and summer and higher concentrations in autumn and winter. In Urumqi, alkanes (38.7%) and oxygenated volatile organic compounds OVOCs (16.7%) were the primary components of VOCs, whereas in Karamay, the proportion of alkanes reached as high as 47.2%, followed by alkenes (13.7%). The ozone formation potential of VOCs in Urumqi and Karamay in summer was 139.2 μg/m³ and 46.7 μg/m³, respectively, mainly contributed by OVOCs (38.2% and 41.8%). In winter, secondary organic aerosol formation potential were 0.59 μg/m³ and 0.41 μg/m³, respectively, mainly contributed by aromatics (89.8% and 84.8%). OH reactivity in Urumqi (5.0 s⁻¹) was higher than that in Karamay (2.6 s⁻¹). Alkenes were found to be the major contributor to OH reactivity. Positive matrix factorization (PMF) source analysis for the two cities revealed great similarity, with the common factors including combustion, traffic exhaust, solvent evaporation, industrial emissions, and regional background. Combustion and traffic exhaust contributed the most to ambient VOCs concentrations in Urumqi and Karamay at 23.8% and 23.5%, respectively, which was high compared with other cities in China.

To explore the spatial-temporal distribution characteristics and meteorological factors impacts of PM_2.5, PM₁₀ and O₃ in the urban agglomeration on the northern slope of Tianshan Mountains, the seasonal variation and spatial-temporal distribution pattern of PM_2.5, PM₁₀ and O₃ were analyzed. Pearson correlation analysis method and generalized additive model (GAM)were used to explore the influence of meteorological factors on atmospheric pollutants. The results showed that 1) in terms of time distribution, PM_2.5 and PM₁₀ were similar, showing winter > spring > autumn > summer, while O₃ showed summer > spring > autumn > winter. 2) In terms of spatial pattern, PM_2.5 and PM₁₀ generally showed a pattern of low in the west and high in the east, and the high concentration area of O₃ was mainly in the Tianshan Tianchi area and Shihezi City in Fukang City. 3) The regional PM_2.5 and PM₁₀ showed significant positive spatial autocorrelation, with high-high agglomeration in the east and low-low agglomeration in the west. 4) Correlation analysis and GAM model showed that PM_2.5, PM₁₀ and O₃ had significant nonlinear response relationship with temperature, humidity, wind speed, air pressure and daily rainfall. The interaction terms between temperature and other meteorological factors all passed the significance test, indicating that there was a significant interaction effect on the influence of PM_2.5, PM₁₀ and O₃. This study presented new conclusions on the mechanism of the influence of meteorological factors on air pollutants in the northern slopes of the northern slope of Tianshan Mountains, as well as an scientific basis for the development of regional air quality management strategies in the region. 

To investigate the pollution characteristics of VOCs in the core area of the Ili River Valley, samples were collected at three typical industrial parks during 2021–2022. The emission characteristics of volatile organic compounds (VOCs), ozone formation potential (OFP) and secondary organic aerosols formation potential (SOAFP) were analyzed, and the health risks for residents were assessed. The results showed that the average TVOCs concentrations in the ambient air of the parks were 189.9±172.1, 129.3±56.0 and 426.4±155.9 μg/m³ for spring, summer and winter. OVOCs was the major component of VOCs for spring and summer with the contribution of 35%−43% and 30%–47% respectively for three industrial parks, while alkane was the primary contributor (64%–70%) for winter. The average OFP of VOCs was 494.5 μg/m3, with OVOCs (19%–47%), aromatics (24%–28%) and isoprene (12%–29%) being the major components. Among them, isoprene, toluene, xylene and methyl methacrylate were the primary reactive species. The average yield of SOAFP was 1.9 μg/m³ and aromatics had a dominant contribution (88%−93%). Toluene, xylene, benzene and ethylbenzene are key species. A potential non-carcinogenic risk from ambient VOCs should be considered for residents living around parks, mainly caused by acrolein. The average lifetime carcinogenic risks (LCR) of benzene, chloroform, tetrachloroethane, 1,2-dichloroethane and 1,2-dibromoethane were above the acceptable level (10⁻⁶), indicating a carcinogenic risk for these species. M/p-Xylene, o-Xylene, and dodecane were key precursors for the collaborative prevention and control of PM_2.5 and O₃. 

To explore the characteristics and sources of water-soluble inorganic ions in PM_2.5 of Kunming, simultaneously on-line measurements of major water-soluble inorganic ions and gaseous pollutants were performed from April 15 to May 20, 2021 in Xishan district, Kunming city using a Gas-aerosol Collector and Ion Chromatograph (GAC-IC). The results showed that the average mass concentration of PM_2.5 was 25.0±15.0 μg/m³, indicating that the atmosphere of Kunming was at a relatively clean level, and the average mass concentration of water-soluble ions was 8.32±4.83 μg/m³, which accounted for 32.1% of the PM_2.5 concentration. The water-soluble components of PM_2.5 and gaseous precursors showed obvious diurnal variation, with the increase of inorganic ion concentrations at night and the decrease of inorganic ion concentrations during the day after reaching their peak in the morning. The average SOR and NOR were 0.55 and 0.042, indicating that there was an obvious secondary transformation process of sulfate, but not of nitrate, which might be accompanied by the formation of nitrate and the decomposition of NH₄NO₃. The result of positive matrix factorization (PMF) indicated that there were five main contribution sources of water-soluble ions in PM_2.5, which were fossil fuel combustion source and industry (36%), secondary sulfate (27%), biomass combustion (18%), secondary nitrate (16%) and sea salt (3%).

In order to study the impact of cross-border transportation of biomass burning from peripheral areas on the air quality in Yunnan Province, a southwestern border province in China, during spring, specifically in response to the large-scale pollution process in Yunnan from April 1 to 18, 2024, three border cities in Yunnan Province, namely Mengzi City, Mangshi City, and Mengla County, were selected as examples. Ground-based particle laser radar network observations, combined with ground air quality data, meteorological data, and MODIS satellite remote sensing data, were used, along with the HYSPLIT backward trajectory model, potential source concentration weight trajectory analysis method, and other technical means, to analyze the spatiotemporal distribution characteristics and motion trajectories of pollutants and to evaluate their impact on the air quality in Yunnan province. The results show that in April 2024, there were numerous fire points in the peripheral areas of Yunnan province. Under the dominance of the southwest monsoon, the three border cities were prone to the cross-border transport of biomass burning from Myanmar, Thailand, Laos, and Vietnam during the period from night to morning, with a lag time of 1.5 to 72 hours and a coverage range of up to 2300 kilometers. During the pollution growth process, the air quality in Mengzi City was mainly affected by mixed-layer transport from Myanmar, Laos, and Vietnam. The transport from eastern Myanmar and passing areas led to an increase of about 30 μg/m³ in the ground PM_2.5 concentration in Mengzi City on the afternoon of April 6th. Mangshi City was mainly affected by surface-level transport and low-altitude subsidence from Myanmar and Bangladesh, while Mengla County was mainly affected by surface-level transport and low-altitude subsidence from Laos, Myanmar and Thailand. Overall, Myanmar has the greatest impact on the air quality of border cities in Yunnan Province. 

The self-organizing mapping neural network clustering (SOM) was utilized to conduct an objective classification study of large-scale samples of atmospheric circulation in Kunming from 2017 to 2019. Meteorological conditions and circulation characteristics of different weather types were assessed by using ground-based ozone concentration and daily ozone pollution data. Findings indicate that there are 9 atmospheric circulation field types in Kunming, with significant differences in occurrence probability and seasonal variation. Different weather types significantly affect the frequency of ozone pollution days (O₃-8h≥160 µg/m³) in Kunming. Among all ozone pollution days, T2 (high pressure ridge in northwest Yunnan) and T6 (westward-moving typhoon) have the highest frequency, accounting for 30.8% and 38.5% of total ozone pollution days respectively, defined as “pollution weather types”. T4, T7, and T8 were classified as “relatively clean weather types” due to absence of ozone pollution, while T1, T3, T5, and T9 are “relatively pollution weather types”. There are significant differences in circulation patterns between T2 and T6. Under the control of T2 weather, Kunming and even the entire Yunnan region are dominated by the westerly wind in front of the high-pressure ridge. Easterly winds surrounding the typhoon affect T6 weather. However, under both circulation conditions, the Kunming and Yunnan region are under the control of high pressure circulation, easily forming high temperature, low humidity, strong radiation, and other environmental conditions conducive to ozone exceeding standards. 

In order to accurately grasp the emission characteristics of anthropogenic air pollutants in Kunming, this study utilizes statistical data from the statistical yearbook and various municipal departments, integrating enterprise surveys, field sampling, and on-site interviews and investigations to establish an anthropogenic emission inventory for Kunming in 2018. The source spectrum data for volatile organic compounds (VOCs) in Kunming were obtained through emission outlet testing at key enterprises and literature research. A detailed list of VOCs sub-species in Kunming was compiled, and their ozone formation potential was calculated. The results showed that the emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_x), carbon monoxide (CO), VOCs, ammonia (NH₃), particulate matter (PM₁₀), fine particulate matter (PM_2.5), black carbon (BC) and organic carbon (OC) in Kunming during 2018 were 13476.92 tons, 53327.85 tons, 397383.83 tons, 55514.73 tons, 20465.41 tons, 75473.99 tons, 29405.57 tons, 1947.53 tons, 4405.39 tons, respectively. Among these, the primary emission sources for NO_x were mobile sources (50.7%), NH₃ were agricultural sources (88.5%), PM₁₀ were dust sources (44.1%) and process sources (43.1%). The main emission sources of CO, VOCs and PM_2.5 were process sources, which accounted for 68.2%, 41.7%, and 51.2% of the emissions of different pollutants, respectively. The primary emission sources for SO₂, BC and OC were stationary combustion sources of fossil fuel, with emission shares of 53.0%, 45.0% and 35.9%, respectively. Pollutants were mainly concentrated in the 5 districts of the main city as well as in Anning City. Within the 5 districts of the main city, pollutants were distributed outward from the center along Youth Road and Renmin Middle Road, with relatively few pollutants found in Chenggong District. SO₂, BC, and OC were mainly distributed by high-value point sources, NO_x, CO, VOCs, and PM_2.5 were distributed by a combination of line and point sources. PM₁₀ presented a spatial distribution characterized by a combination of point and surface sources. NH₃ showed a significant spatial distribution characteristics of surface sources. VOCs sub-species inventory emissions were dominated by aromatic hydrocarbons and alkanes, with the main sources being vehicle emissions and architectural coatings, as well as the industrial solvent. Ozone formation potentials (OFP) for aromatic hydrocarbons accounted for up to 49.9%, with species such as (m- and p-) xylene, toluene, and ethylene comprising a relatively high proportion of the VOCs species. 

To investigate the causes of ozone pollution in Kunming city during the spring season, a field atmospheric experiment was conducted at Yijingyuan Hotel, Kunming city, from April 15 to May 20, 2021. The study analyzed the variation patterns of atmospheric photochemical pollutants in Kunming city during the spring season, and a box model was utilized to simulate the local chemical generation of ozone and the sensitivity of its formation.The results showed that during the observation period, the ozone pollution precursors volatile organic compound (VOCs), nitrogen dioxide (NO₂)and carbon monoxide (CO) in Kunming increased significantly, the photochemical reaction activity was strong, and the photochemical generation played a significant role in the initiation and aggravation stages of ozone pollution. The peak values of ozone formation rate F(O₃) were close to 20×10⁻⁹ h⁻¹ and 16×10⁻⁹ h⁻¹, respectively. The results indicate that Kunming is in a VOCs-limited area. In addition to reducing anthropogenic VOCs such as alkenes and aromatics, controlling the CO concentration is also an effective way to control ozone pollution.

The first nitrous acid (HONO) observation was conducted in Kunming of Yunnan Province, from April to May 2021 with frequent ozone (O₃) pollution events. To evaluate the impact of HONO on O₃, the WRF-Chem model simulations were conducted, with two cases including or excluding potential HONO sources. Based on the comparison between simulations and the corresponding observations, it was found that the application of the MEIC inventory (version 2020) could reasonably simulate HONO, nitrogen dioxide (NO₂), O₃ and fine particulate matter (PM_2.5) in urban Kunming. The additional HONO sources noticeably enhanced atmospheric oxidation capacity in Kunming and accelerated the hydroxyl radical (OH) production rate, leading to an O₃ enhancement of (2–6)×10⁻⁹ with the corresponding percentage enhancement of 2%–8% at the Kunming site within the height of 0–4 km and an O₃ enhancement of (4–7)×10⁻⁹ near the ground at the Kunming site and its surrounding area. The O₃-VOCs-NO_x sensitivity was also influenced by the potential HONO sources. This study deepened the understanding of HONO, atmospheric oxidation capacity and O₃ formation in the Yunnan-Guizhou Plateau, and could be helpful for regional O₃ pollution control. 

Using the stems of Dendrocalamus membranaceus Munro as raw materials, pyrolysis char BC-700 and hydrochar HBC-190/700 were prepared by the high-temperature pyrolysis method and the hydrothermal roasting method, respectively. Then, their benzene adsorption performance was evaluated at 55°C. The results showed that the adsorption effect of biochar HBC-190/700 on benzene was three times that of BC-700. Furthermore, the influence of preparation methods on the physical and chemical properties of the adsorbents was investigated using characterization techniques such as BET, XRD, SEM, Raman and FT-IR. SEM results indicated that many carbon microspheres were accumulated on the surface of hydrothermal carbon HBC-190/700, resulting in the formation of crevice pores. BET analysis showed that the hydrothermal carbon HBC-190/700 presented a hierarchical pore distribution of micropores and mesopores, which was conducive to the mass transfer of benzene. In addition, FT-IR analysis revealed that the aromatic functional groups of HBC-190/700 were the key factors for benzene adsorption. 

In the future, China’s power sector needs to develop under the constraints of the triple objectives of power supply security, decarbonization and power economics. Given the complexity, nonlinearity and uncertainty of the power sector, an analysis of the low-carbon development path of China’s power sector using system dynamics modeling reveals that, based on the coal-dominated national conditions, China should reasonably control the growth rate of thermal power through power and carbon market price constraints, orderly deploy energy storage facilities to ensure the stability of the system and promote the rational development of renewable energy sources, accelerate the application of carbon capture and storage (CCS) to effectively reduce power carbon emissions, and incentivize CCS innovation and development through revenue distribution from carbon emission quota auctions.

Based on the hydrogen and oxygen isotope data of water bodies, this study identifies the streamflow components of the mainstream channels using the MixSIAR mixed model for 22 sample sub-basins in the Tarim Basin. The relationships between streamflow components and basin characteristics for endorheic rivers were analyzed by further combining climate and underlying surface conditions of sub-basins. It appears that the sub-basins in the southern Tarim Basin primarily rely on precipitation for their streamflow, accounting for 39%−55%, 23%−30%, 22%−32% for precipitation, and glacial meltwater sources, respectively. The sub-basins located in the oasis area of the northern Tarim River are predominantly influenced by groundwater recharge, with a component proportion of 14%−32%, 44%−76%, 0%−39% for streamflow sources. Furthermore, the sub-basins primarily supplied by meltwater are predominantly found in the southwest region of the Tarim Basin, with a proportion of 29%−33%, 14%−31%, 40%−53%. Among various basin factors examined, actual evaporation, soil water content, vegetation index, and area proportion of desert area and glacier area emerged as key influencing factors on streamflow composition for the sub-basins of the Tarim Basin. It was also found that basin underlying surface conditions substantially impact variations in streamflow components. This result provides a scientific foundation for effective water resources management and ecological preservation within inland river basins amidst changing climatic conditions. 

A mesoscale convective system (MCS) embedded in a cold frontal cloud system over Beijing on July 16, 2018 was investigated using X-band dual-polarization radar observations from Fangshan Station and sounding data from the Beijing Observatory. This study focused on hydrometeor identification and microphysical characterization, yielding the following key findings. 1) The ice-phase hydromorphic species above the 0°C layer differed in different stages and regions of this MCS. From the stage of development to maturity to dissipation, the main hydromorphic species in the region with combined reflectance larger than 40 dBZ were graupel and snow, and the proportion of ice crystals was relatively low. In the region with combined reflectance between 20 and 40 dBZ, graupel, snow, and ice crystals were the main hydromorphic species. In these two regions, the proportion of graupel gradually decreased with time, while the proportion of snow and ice crystals gradually increased with time. In the region with combined reflectance smaller than 20 dBZ, the proportion of graupel was very low, and the main hydromorphic species were snow and ice crystals, with the proportion of snow gradually decreasing with time, and the proportion of ice crystals gradually increasing with time. 2) The area of the 20–40 dBZ echo region in this MCS played a dominant role in precipitation area. 3) At the beginning of convection, satellite brightness temperature observation had a better monitoring effect on precipitation. The application of X-band dual-polarization radar data to analyze the microphysical characteristics of MCS is beneficial to understand the microphysical processes occurring in the system, and can provide a useful reference for the revision of the microphysical parameterization scheme. 

Based on the characteristics of space particle radiation in the sun-synchronous orbit (SSO), a space particle radiation effect comprehensive measuring instrument (SPRECMI) was installed on the orbital platform of upper stage of Chinese CZ-4C carrier rocket for obtaining the high-energy proton energy spectra, linear energy transfer (LET) spectra of particles, and radiation dose rate. The detection results can be used for in-orbit fault analysis and operational control management of spacecraft and serve as reference data for component validation tests. After SPRECMI’s development, accelerator calibration and simulations were conducted, and the results demonstrated that the measured indicators such as high-energy protons, total radiation dose, and LET spectrum all met the requirements of detection range, accuracy, and sensitivity. Furthermore, the in-orbit flight test revealed that the detection results of the load components were consistent with the physical characteristics of the particle radiation environment of the spacecraft orbit.

An Ms 7.1 earthquake struck Wushi County in Aksu Prefecture, Xinjiang at 02:09:05 on January 23, 2024. We conducted a preliminary investigation into the surface deformation characteristics at the epicenter (41.26°N, 78.63°E) and adjacent areas. The observation results show that the fault which triggered the earthquake was not widely exposed in the epicenter area. The primary surface deformations observed are mainly tensional fractures, with locally observed compression bulges, scarps and sand liquefaction. The earthquake caused approximately 5 cm of vertical displacement. The fracture zone composed of multiple tensional fractures destroyed roads, mountains and houses, and led to collapses and landslides in mountainous areas. Based on our field investigation, focal mechanism solution and aftershock distribution, it is concluded that the seismogenic structure of the earthquake is the eastern segment of Maidan fault. The future earthquake risk in this region remains high. Considering the potential risks associated with surface deformation, we recommend that local government strengthen the earthquake resistance capacity of building in pastoral areas and enhance the investigation and management of secondary geological hazards.

Regarding the large-scale gravity field response in the Tethyan tectonic domain, this work aims to connect specific wavelength of geoid anomaly with the mantle structure caused by Tethys evolution. To acheive this, spherical harmonic spectrum analysis and kernel analysis on global geoid are employed, and the global geoid is further calculated by forward modeling with the mantle structure obtained by global seismic tomography. Density structure in our geoid calculation is obtained by seismic tomography. Through spherical harmonic analysis of global geoid observation, the geoid anomalies of the Tethyan tectonic domain exhibit a spherical harmonic degree 7 wavelength scale. Analysis of geoid kernels provides initial constraints on the density source depth of Tethyan geoid anomalies. Finally, through global geodynamic numerical modeling, the degree 7 density anomaly at depths of 425–1000 km in the mantle corresponds well with the Tethyan geoid anomalies in the Indonesian, Burmese, Tibetan Plateau, and Zagros regions. Preliminarily, the observed degree 7 geoid anomalies indicate slab remnants in the central and eastern segments of the Tethys at depths of 425–1000 km in the mantle.