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Microplastics (MPs) are emerging pollutants, and limited research has focused on their exposure to terrestrial wildlife and transport mode on the remote Tibetan Plateau (TP). Therefore, we investigated MPs in the southern soil and feces of Equus kiang (Tibetan wild ass), a species peculiar to the TP, which is known as the "third pole." We found that MP median abundances were 102 and 4.01 particles/g of dry feces and soil, respectively. In both media, the MP morphology mainly comprised ∼50 μm slender fibrous particles. In total, 29 MP types were identified in the feces, compared to 26 types in the soil. Among them, the acrylate copolymer (35.9%) and polyurethane (24.9%) were predominant in the feces, while polyurethane (22.5%) and silicone (20.4%) were predominant in the soil. After ingesting MPs at one location, E. kiang may become a source of MP pollution when moving to other meadows on the TP. The potential MP transport flux of a herd of 20 kiangs has been estimated at 1736 particles m −2 a −1 . A unique "source−sink−source" MP transport model comprising an "atmospheric deposition−vegetation−feces−atmosphere" cycle on the TP was observed based on atmospheric transport simulations and terrestrial food chain transfer processes. Owing to human settlements in south and East Asia adjacent to the TP, atmospheric long-distance transmission is an essential route for MPs to enter the TP.

Long-term monitoring of changes in the concentration of radionuclides in the atmosphere can provide valuable information for studying atmospheric dynamics (Yamagata et al., 2019;Zhang et al., 2021). Radionuclides 7 Be (T 1/2 = 53.29 d) and 10 Be (T 1/2 = 1.36 Ma) (Nishiizumi et al., 2007) are produced by the collision of high-energy cosmic ray flux with nitrogen atoms and oxygen atoms in the atmosphere. After generation, 7 Be and 10 Be are adsorbed on submicron aerosols, and their lifetimes are determined by the residence time of the aerosols (Lal et al., 1958). Since the sources of 7 Be and 10 Be are controlled only by cosmic rays, and mainly produced at the lower of the stratosphere and the top of the troposphere (Brown et al., 1989), the variation of 7 Be concentration in the near-surface air is generally observed to trace atmospheric mass transport processes (Bhandari et al., 1966). However, in addition to stratosphere-troposphere exchange variability, local effects (such as local

Abstract. Locally rapid stratospheric air intrusions facilitate the transport of stratospheric material to the troposphere. Long-term continuous monitoring of such events by traditional techniques, such as sounding technology, is challenging. Beryllium-7 (7Be) and beryllium-10 (10Be) offer an alternative. These isotopes are formed by cosmic rays and are mainly produced in the lower stratosphere and upper troposphere. Due to their similar geochemical properties and substantial difference in half-lives favor relatively high 10Be / 7Be ratios in the stratosphere, as compared to the troposphere. Monitoring surface 10Be / 7Be ratios affords a potential means to identify stratospheric air intrusions. However, high temporal resolution 10Be / 7Be observational records must be taken and corrected for dust-borne 10Be to identify stratospheric air intrusions. In this study, we use Accelerator Mass Spectrometry to measure both 7Be and 10Be in rain and aerosol (down to ~ 200 cubic meters air) with an error of ~ 1.5 %. We correct for dust-borne 10Be using soil Al. This method provides precise measurements with daily resolution. We present annual beryllium isotopes (7Be, 10Be, and 10Be / 7Be ratio) record for the Chinese Loess Plateau that includes several regional sites. We show that for the city of Xi'an, the proportion of dust-borne (resuspended) 10Be was ~24 % in 2020/21. Our results confirm that stratospheric air intrusion events in the Loess Plateau are frequent and rapid throughout the year and are strongest in the spring (March–July), when 10Be / 7Be values were observed to increase about a factor of 3. Even in winter, weaker stratospheric air intrusion events can be detected. Calculated Δ(10Be / 7Be) values in winter suggest stratospheric ozone transport can lead to an ~25 % cumulative increase the surface ozone.