Atmospheric precipitation chemistry and environmental significance in major anthropogenic regions globally

In order to investigate the spatiotemporal distribution and influencing factors of global precipitation chemistry, we conducted a comprehensive analysis using multiple data sources, revealing the impact of human activities on the natural environment. The results indicate a decreasing trend in global precipitation acidity over the past 20 years. The distribution of global precipitation is influenced by both natural and anthropogenic factors. Alkaline cation concentrations are higher in desert and arid regions, while high concentrations of SO42- and NO3- are primarily found in industrial areas, and agricultural areas exhibit higher NH4+ concentrations. Coastal regions have higher Na+ and Cl- concentrations compared to inland areas. However, the increased Na + and Cl- concentrations due to inland salinization should not be overlooked. Additionally, influenced by atmospheric circulation, transboundary pollution from South Asia leads to higher SO42- and NO3- concentrations in precipitation over the Tibetan Plateau. Meteorological factors have a weaker influence on precipitation chemistry compared to geographical and human activity factors, although ion concentrations in snowfall are higher than in rainfall.

Water-soluble inorganic ions (WSIs) in the aerosols from Central Asia via transboundary transport measured in Jimunai in 2020

Air pollution is a global issue that often transcends national borders, leading to disputes over environmental concerns and climate-mitigation responsibilities. Between March and July 2020, we collected aerosol samples in Jimunai, a town in western China neighboring Kazakhstan, to assess transboundary air pollution in the region. Our analysis focused on major water-soluble inorganic ions (WSIs), with Ca2+ and SO42- accounting for almost 60% of the total ion loading. The ratio of cations to anions was greater than one (1.33 ± 0.27), indicating alkaline aerosols during the sampling period. Our results suggest that the pollutants measured were primarily sourced from Kazakhstan, as demonstrated by local meteorological data, air-mass trajectory analysis, and pollutant emission inventories in Kazakhstan. Correlation and primary component analysis indicated that NH4+ played an important role in neutralizing NO3- and SO42-, while Cl- was significantly depleted by the probable reaction HNO3↑ + NaCl = HCl↑ + NaNO3. These findings highlight the need for continued monitoring and regulation of air pollution sources in the region to address transboundary air pollution.

Transboundary watershed pollution control analysis for pollution abatement and ecological compensation

The effect of watershed environmental management is closely related to the cooperation modes of upstream and downstream regions pollution control, but the existing literature rarely considers it. Additionally, based on the cumulative and cross-border impacts of pollution discharge in different regions, it is appropriate to use dynamic game theory to study pollution control problems. Therefore, this paper develops a dynamic multi game model to analyze the pollution control game behavior between the upstream and downstream regions along the basin in three scenarios: non-cooperation, pollution abatement cooperation, and ecological compensation. By using the optimal control method, we get the dynamic equilibrium strategies of the government and enterprises and pollution stock trajectories under different cooperation modes. The results show that pollution abatement cooperation can improve the environment, but may not improve social welfare; the eco-compensation mechanism is not always conducive to the improvement of the environment and welfare of the basin, and the effective conditions of implementing ecological compensation is put forward. In addition, we also analyzed the impact of consumer preferences, pollution treatment efficiency, and other parameters on governments and enterprises decision-making and the social welfare. These conclusions provide a theoretical basis for cooperative governance scheme for transboundary pollution in river basin.

The role of boundary layer height in India on transboundary pollutions to the Tibetan Plateau

The aerosols over the Tibetan Plateau (TP) play an important role in radiative budget and hydrologic cycle over Asia even the northern hemisphere. Adjacent to the major emission sources of air pollutants, transboundary pollutions transported to the TP due to the unique geographical location and climatic characteristics, is an important exogenous driver of multi-layer changes over the TP. The influence of boundary layer height (BLH) in India to the transboundary pollution over the TP from 1980 to 2018 was investigated in the study. Results showed that air pollutants transported to the TP is more efficient within the boundary layer compared with free troposphere. The BLH decreases with the rate of 1.8 m/season in these decades. Moreover, it also has a significant correlation with AOD (-0.4). Accompanied with westerly wind and the topographic forcing in the higher boundary layer, dust particles were uplifted from the northern India to the high altitude. Compared with a higher BLH, the lower BLH is difficult for the long transport of pollutants with weaker westerly wind over the TP and its difference of dust concentration with 0.2 μg m^-3 in the upper troposphere. The solar radiation enhancement increases the sensible heat and accelerate the upward of the atmosphere in high BLH events, which uplifts the pollutants accumulated in lower troposphere to higher altitudes and provides thermodynamic conditions for the pollutants transorted to the TP with westerly winds. This study provides confidence for the source, long-term transport of the TP aerosol, and its environmental and climatic impacts on climate systems in the Northern Hemisphere.

Migration and diffusion characteristics of air pollutants and meteorological influences in Northwest China: a case study of four mining areas

In the process of exploiting mineral resources, dust enters the environment through air suspended particles and surface runoff, which has a serious impact on the atmospheric environment and human health. From all-year and seasonal scenarios, the migration trajectories and cumulative concentration based on the secondary development of Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) in four mining areas (SF, BC, SJZ, and MJT) in Northwest China are studied. The convergent cross mapping (CCM) method is used to study the causal relationship between concentration and meteorological factors. In this process, the problem of missing non-station meteorological data is solved with the help of the inverse distance weighted interpolation method, and the problem in which the convergence requirements of the CCM algorithm cannot meet the requirements is solved with the bootstrap method. The results indicated that the short path has the characteristics of slow movement, short migration path, low altitude(< 1 km), and high contribution rate, while the long path has the opposite characteristics. Furthermore, the results demonstrated that the concentration is centered on the pollution source and diffuses around, with a diffusion radius of 220-270 km, showing a serious pollution center and slight gradient settlement on the edge, but the overall distribution of accumulated concentration is uneven. The results also show that temperature (TEMP and S_TEMP), evaporation, and air pressure are the main meteorological factors affecting the all-year concentration. The concentration and meteorological factors in the four mining areas also show significant seasonal characteristics, and the correlation in spring, summer, and autumn is stronger than that in winter. This study not only provides a reference for the green and sustainable exploitation of mineral resources but also provides theoretical support for the joint prevention and control of transboundary pollution.

Local and transboundary impacts of PM2.5 sources identified in Seoul during the early stage of the COVID-19 outbreak

Countries in Northeast Asia have been regulating PM_2.5 sources and studying their local and transboundary origins since PM_2.5 causes severe impacts on public health and economic losses. However, the separation of local and transboundary impacts is not fully realized because it is impossible to change air pollutant emissions from multiple countries experimentally. Exceptionally, the early stage of the COVID-19 outbreak (January-March 2020) provided a cross-country experiment to separate each impact of PM_2.5 sources identified in Seoul, a downwind area of China. We evaluated the contributions of PM_2.5 sources compared to 2019 using dispersion normalized positive matrix factorization (DN-PMF) during three meteorological episodes. Episodes 1 and 2 revealed transboundary impacts and were related to reduced anthropogenic emissions and accumulated primary pollutants in Northeast China. Anthropogenic emissions, except for the residential sector, decreased, but primary air pollutants accumulated by residential coal combustion enhanced secondary aerosol formation. Thus, the contributions of sulfate and secondary nitrate increased in Seoul during episode 1 but then decreased maximally with other primary sources (biomass burning, district heating and incineration, industrial sources, and oil combustion) during episode 2 under meteorological conditions favorable to long-range transport. Local impact was demonstrated by atmospheric stagnation during episode 3. Meteorological condition unfavorable to local dispersion elevated the contributions of mobile and coal combustion and further contributed to PM_2.5 high concentration events (HCE). Our study separates the local and transboundary impacts and highlights that cooperations in Northeast Asia on secondary aerosol formation and management of local sources are necessary.

Inequality in historical transboundary anthropogenic PM2.5 health impacts

Atmospheric transport of fine particulate matter (PM_2.5), the leading environmental risk factor for public health, is estimated to exert substantial transboundary effects at present. During the past several decades, human-produced pollutant emissions have undergone drastic and regionally distinctive changes, yet it remains unclear about the resulting global transboundary health impacts. Here we show that between 1950 and 2014, global anthropogenic PM_2.5 has led to 185.7 million premature deaths cumulatively, including about 14% from transboundary pollution. Among four country groups at different affluence levels, on a basis of per capita contribution to transboundary mortality, a richer region tends to exert severer cumulative health externality, with the poorest bearing the worst net externality after contrasting import and export of pollution mortality. The temporal changes in transboundary mortality and cross-regional inequality are substantial. Effort to reduce PM_2.5-related transboundary mortality should seek international collaborative strategies that account for historical responsibility and inequality.

Transboundary pollution control in asymmetric countries: do assistant investments help?

Transboundary pollution control usually requires the cooperation of neighboring countries due to the externality of pollution. However, countries at different levels of development, which are called asymmetric countries in this paper, may have different attitudes toward this cooperation. The developing countries would like to take a free ride and they can benefit from the cooperation with developed countries, but the developed countries may not be willing to afford this cooperation cost. This paper discusses the cooperation between two asymmetric countries that developed country may provide assistant investments to help the developing country reduce pollution stock. We consider a dynamic differential game to model the transboundary pollution control between two asymmetric regions and derive the optimal equilibrium of both regions using the Hamilton-Jacobi-Bellman (HJB) equation. To explore the impact of assistant investments, numerical illustrations and sensitivity analysis are implemented to compare the equilibrium strategies under two scenarios: that with or without assistant investments. We conclude that the common pollution stock will be reduced when the developed country is willing to provide assistant investments to the developing country. Besides, the equilibrium emission strategies of both countries increase with assistant investments, which means more economic benefits for both sides.

The Korea-United States Air Quality (KORUS-AQ) field study

The Korea-United States Air Quality (KORUS-AQ) field study was conducted during May-June 2016. The effort was jointly sponsored by the National Institute of Environmental Research of South Korea and the National Aeronautics and Space Administration of the United States. KORUS-AQ offered an unprecedented, multi-perspective view of air quality conditions in South Korea by employing observations from three aircraft, an extensive ground-based network, and three ships along with an array of air quality forecast models. Information gathered during the study is contributing to an improved understanding of the factors controlling air quality in South Korea. The study also provided a valuable test bed for future air quality-observing strategies involving geostationary satellite instruments being launched by both countries to examine air quality throughout the day over Asia and North America. This article presents details on the KORUS-AQ observational assets, study execution, data products, and air quality conditions observed during the study. High-level findings from companion papers in this special issue are also summarized and discussed in relation to the factors controlling fine particle and ozone pollution, current emissions and source apportionment, and expectations for the role of satellite observations in the future. Resulting policy recommendations and advice regarding plans going forward are summarized. These results provide an important update to early feedback previously provided in a Rapid Science Synthesis Report produced for South Korean policy makers in 2017 and form the basis for the Final Science Synthesis Report delivered in 2020.

Can China's pollution reduction mandates improve transboundary water pollution?

This paper discusses how the pollution prevention mandate imposed by China's central government triggers water pollution across provincial borders. Because the central government has put the pollutant reduction into the promotion evaluation, and pollution control in the downstream area of a province mainly brings benefit to other regions, the provincial officials are incentivized to reduce the water pollutants away from the downstream city and strengthen environmental regulation within the province. We apply the difference-in-differences-differences (DDD) method to the dataset on water quality in cities along 18 major rivers in China from 2007 through 2016. We find that compared with the interior cities, the most downstream city of a province faces worse water quality. Besides, we find that environmental policy significantly increases the extent of pollution across jurisdictional boundaries. Then, we turn on the mechanism and find that the pollutant reduction target is significantly lower in the most downstream city of a province. Unanticipated provincial government behavior leads to severe transboundary water pollution.

Turnover of environmental protection officials and transboundary water pollution

Considering the situation of the frequent turnover of Chinese environmental protection officials (EPOT), this paper analyzes its impact on transboundary water pollution. The results show that EPOT can reduce transboundary pollution. EPOT can reduce the concentration of DO by 0.261 and NH3-N by 0.167 in the downstream river. And the impact shows a first strong and then weak change over time. EPOT can restrain transboundary pollution by reducing the production of polluting enterprises and promoting public pollution reporting, and it aggravates transboundary pollution by reducing environmental law enforcement and collaborative governance. In addition, the impact of EPOT on transboundary pollution has a distance effect. Within the regulatory distance of 50 km, EPOT has strong inhibition on transboundary pollution. When the governor and the environmental protection official (EPO) change tenure at the same time, the inhibition of transboundary pollution is the strongest. In addition, EPOs from the central government and with working experience in environmental protection departments can control transboundary pollution better.

Time-resolved characterization of organic compounds in PM2.5 collected at Oki Island, Japan, affected by transboundary pollution of biomass and non-biomass burning from Northeast China

To evaluate the transboundary pollution of organic aerosols from Northeast Asia, a highly time-resolved measurement of organic compounds was performed in March 2019 at Oki Island located in Japan, which is a remote site and less affected by local anthropogenic sources. PM_2.5, water-soluble organic carbon (WSOC) concentrations, and WSOC fraction in PM_2.5 showed high values on March 22-23 (high-WSOC period (HWSOC)) when the air mass passed through the area where many fire spots were detected in Northeast China. Biomass burning tracers showed higher concentration, especially levoglucosan exceeded 1 μg/m³ during the HWSOC than the low-WSOC period (LWSOC). Notably, high time-resolved measurements of biomass burning tracers and back trajectory analysis during HWSOC revealed a difference in the variation of lignin pyrolyzed compounds and anhydrous sugars on 22 and 23 March. The air mass passed to different areas in Northeast China in which fire spots were detected, such as the eastern area on the 22nd and the western area on the 23rd. Almost-organic compounds also showed high concentration and strong correlations with levoglucosan and sulfate during HWSOC. Moreover, low-carbon dicarboxylic acids (e.g., adipic acid) and secondary products from anthropogenic volatile organic compounds (e.g., 2,3-dihydroxy-4-oxopentanoic, phthalic, 5-nitrosalicylic acids), also showed a strong correlation with sulfate ions during the HWSOC and LWSOC, respectively. These higher concentrations and strong correlations with levoglucosan and sulfate during the HWSOC propose that their generation could be enhanced by biomass burning. The ratios of organics (e.g., levoglucosan/mannnosan, pinic/3-methylbutane-1,2,3-tricarboxylic acids) suggest that the high concentrations of PM_2.5 and WSOC observed during the HWSOC were caused by aged organic aerosols that originated from the combustion of herbaceous plants transported from Northeast China. Our findings indicate that biomass combustion in Northeast China could significantly affect the chemical compositions and the characterization of organic aerosols in downwind regions of Northeast China.

Can regional integration control transboundary water pollution? A test from the Yangtze River economic belt

Based on the quasi-natural experiment of the establishment of the Yangtze River economic belt, this paper uses a difference-in-difference-in-differences model (DDD) to test the impact of regional integration on transboundary pollution. The results show that regional integration can significantly reduce transboundary water pollution. Regional integration reduces chemical oxygen demand (COD) by 0.357, ammonia nitrogen content (NH₃-N) by 0.155, and dissolved oxygen content (DO) by 0.088 in the downstream of the provincial boundary. And regional integration has a long-term inhibitory effect on transboundary pollution. The heterogeneity results show that the regional integration has a stronger inhibition effect on the transboundary pollution of the middle and lower reaches of the Yangtze River economic belt and the tributaries. At the government level, regional integration can reduce transboundary pollution by strengthening the government's environmental regulation and collaborative governance. At the industry level, it can inhibit transboundary pollution by promoting industrial structure optimization and green technology innovation. At the market level, regional integration can promote market competition to reduce transboundary pollution and expand market scale to intensify transboundary pollution. At the society level, regional integration can intensify transboundary pollution by promoting population agglomeration and effectively alleviate transboundary pollution by enhancing public environmental supervision.

Mitigating the air pollution effect? The remarkable decline in the pollution-mortality relationship in Hong Kong

Using transboundary pollution from mainland China as an instrument, we show that air pollution leads to higher cardio-respiratory mortality in Hong Kong. However, the air pollution effect has dramatically decreased over the past two decades: before 2003, a 10-unit increase in the Air Pollution Index could lead to a 3.1% increase in monthly cardio-respiratory mortality, but this effect has declined to 0.5% using recent data and is no longer statistically significant. Exploratory analyses suggest that a well-functioning medical system and immediate access to emergency services can help mitigate the contemporaneous effects of pollution on mortality.

Mercury isotopes in frozen soils reveal transboundary atmospheric mercury deposition over the Himalayas and Tibetan Plateau

The concentration and isotopic composition of mercury (Hg) were studied in frozen soils along a southwest-northeast transect over the Himalaya-Tibet. Soil total Hg (Hg_T) concentrations were significantly higher in the southern slopes (72 ± 54 ng g^-1, 2SD, n = 21) than those in the northern slopes (43 ± 26 ng g^-1, 2SD, n = 10) of Himalaya-Tibet. No significant relationship was observed between Hg_T concentrations and soil organic carbon (SOC), indicating that the Hg_T variation was not governed by SOC. Soil from the southern slopes showed significantly negative mean δ²⁰²Hg (-0.53 ± 0.50‰, 2SD, n = 21) relative to those from the northern slopes (-0.12 ± 0.40‰, 2SD, n = 10). The δ²⁰²Hg values of the southern slopes are more similar to South Asian anthropogenic Hg emissions. A significant correlation between 1/Hg_T and δ²⁰²Hg was observed in all the soil samples, further suggesting a mixing of Hg from South Asian anthropogenic emissions and natural geochemical background. Large ranges of Δ¹⁹⁹Hg (-0.45 and 0.24‰) were observed in frozen soils. Most of soil samples displayed negative Δ¹⁹⁹Hg values, implying they mainly received Hg from gaseous Hg(0) deposition. A few samples had slightly positive odd-MIF, indicating precipitation-sourced Hg was more prevalent than gaseous Hg(0) in certain areas. The spatial distribution patterns of Hg_T concentrations and Hg isotopes indicated that Himalaya-Tibet, even its northern part, may have been influenced by transboundary atmospheric Hg pollution from South Asia.

Surface ozone climatology of South Eastern Brazil and the impact of biomass burning events

In the austral spring, biomass fires affect a vast area of South America each year. We combined in situ ozone (O₃) data, measured in the states of São Paulo and Paraná, Brazil, in the period 2014-2017, with aerosol optical depth, co-pollutants (NOx, PM_2.5 and PM₁₀) and air backtrajectories to identify sources, transport and geographical patterns in the air pollution data. We applied cluster analysis to hourly O₃ data and split the investigation area of approximately 290,000 km² into five groups with similar features in terms of diurnal, weekly, monthly and seasonal O₃ concentrations. All groups presented a peak in September and October, associated with the fire activities and enhanced photochemistry. The highest mean O₃ concentrations were measured inland whilst, besides having lower concentrations, the coastal group was also associated with the smallest diurnal and seasonal variations. The latter was attributed to lower photochemical activity due to frequently occurring overcast weather situation. The mean annual regional contribution of O₃ over the area was 61 μg/m³, with large seasonal and intersite variabilities (from 35 to 84 μg/m³). The long-range transport of smoke contributed with between 23 and 41% of the total O₃ during the pollution events. A pollution outbreak in September 2015 caused many-fold increases in O₃, PM_2.5 and PM₁₀ across the investigation area, which exceeded the World Health Organisation recommendations. We show that the regional transport of particulates and gas due to biomass burning overlays the local emissions in already highly polluted cities. Such an effect can outweigh local measures to curb anthropogenic air pollution in cities.

Atmospheric deposition of anthropogenic inorganic nitrogen in airborne particles and precipitation in the East Sea in the northwestern Pacific Ocean

The atmospheric deposition of anthropogenic nitrogen is an increasingly important new source of nitrogen to the ocean. Coastal areas east of the Korean Peninsula are suitable for the investigation of the effects of atmospheric anthropogenic nitrogen on the ocean nutrient system because of the low riverine discharge rates and the prevailing influence of the East Asian outflow. Thus, we measured the concentrations of nitrate (NO₃^-) and ammonium (NH₄⁺) in airborne particles and in precipitation from March 2014 to February 2016 at a coastal site (37.08°N, 129.41°E) on the east coast of Korea. The dry deposition of NO₃^- (27-30 mmol N m^-2 yr^-1) was far greater than that of NH₄⁺ (6-8 mmol N m^-2 yr^-1). The greater rate of dry NO₃^- deposition was associated with air masses traveling over northeastern China and central Korea. In contrast, the rates of wet deposition of NO₃^- (17-24 mmol N m^-2 yr^-1) and NH₄⁺ (14-27 mmol N m^-2 yr^-1) were comparable and were probably associated with in-cloud scavenging of these ions. The results indicate that the total deposition of NO₃^- and NH₄⁺ combined could contribute to ~2.4% and ~1.9% of the primary production in the coastal areas east of the Korean Peninsula and in the East Asian marginal seas, respectively, which would be a lower bound because the dry deposition of reactive nitrogen gas was not included. Our study shows that the atmospheric input of anthropogenic NO₃^- and NH₄⁺ may substantially increase phytoplankton biomass in the coastal waters of the East Sea near the Korean Peninsula.

Sources and outflows of atmospheric mercury at Mt. Changbai, northeastern China

Atmospheric gaseous elemental mercury (GEM), particulate bound mercury (PBM), and gaseous oxidized mercury (GOM) were continuously measured at a remote site in northeastern China from July 2013 to July 2014. Mean (±1SD) concentrations of the hourly data of GEM, PBM, and GOM were 1.68 ± 0.47 ng m^-3, 16.6 ± 15.2 pg m^-3, and 5.4 ± 6.4 pg m^-3, respectively. Concentration-weighted trajectory (CWT) analysis suggested that the potential source regions of GEM and GOM observed at this site were northern and eastern China. GEM and GOM CWT values significantly correlated with anthropogenic Hg emissions, suggesting that long-range transport of anthropogenic Hg emissions played an important role in GEM and GOM pollutions in remote areas of northeastern China. On the other hand, long-range transport of anthropogenic PBM emissions from eastern and northeastern China combined with large-scale biomass burning in Northeast Asia likely dominated PBM pollution. Principal component analysis (PCA) results, making use of the combined data sets of speciated atmospheric Hg, trace elements, and meteorological parameters, suggested that coal combustion and non-ferrous metal smelting contributed significantly to all the Hg species at this site, while the other anthropogenic sources in China also had a major impact on GEM. Forward air mass trajectory analysis revealed that outflows of GEM from northeastern China may have a potential impact on GEM pollutions in remote and oceanic areas in Northeast Asia.

Source tagging modeling study of regional contributions to acid rain in summer over Liaoning Province, Northeastern China

Strong acid rain was recently observed over Northeastern China, particularly in summer in Liaoning Province where alkaline dust largely neutralized acids in the past. This seems to be related to the regional transboundary pollution and poses new challenges in acid rain control scheme in China. In order to delve into the regional transport impact, and quantify its potential contributions to such an "eruption" of acid rain over Liaoning, this paper employs an online source tagging model in coupling with the Nested Air Quality Prediction Modeling System (NAQPMS). Validation of predictions shows the model capability in reproducing key meteorological and chemical features. Acid concentration over Liaoning is more pronounced in August (average of 0.087 mg/m³) with strong pollutant import from regional sources against significant depletion of basic species. Seasonal mean contributions from regional sources are assessed at both lower and upper boundary layers to elucidate the main pathways of the impact of regional sources on acid concentration over Liaoning. At the upper layer (1.2 km), regional sources contribute to acid concentration over Liaoning by 67%, mainly from Shandong (16%), Hebei (13%), Tianjin (11%) and Korean Peninsula (9%). Identified main city-receptors in Liaoning are Dandong, Dalian, Chaohu, Yingkou, Liaoyang, Jinfu, Shengyang, Panjin, Tieling, Benxi, Anshan and Fushun. At lower layer (120 m) where Liaoning local contribution is dominant (58%), regional sources account for 39% in acid concentration. However, inter-municipal acid exchanges are prominent at this layer and many cities in Liaoning are revealed as important sources of local acid production. Seasonal acid contribution average within 1.2 km-120 m attains 55%, suggesting dominance of vertical pollutant transport from regional sources towards lower boundary layer in Liaoning. As direct environmental implication, this study provides policy makers with a perspective of regulating the regional transboundary environmental impact assessment in China with application to acid rain control.

Comparison of moss and pine needles as bioindicators of transboundary polycyclic aromatic hydrocarbon pollution in central Japan

Atmospheric pollution by polycyclic aromatic hydrocarbons (PAHs) has become a serious problem, especially in Asia, as PAHs can severely affect ecologically important mountainous areas. Using pine needles and mosses as bio-indicators, this study examined PAH pollution in a mountainous study area and evaluated the influence of transboundary PAHs. PAHs in urban areas were also evaluated for comparison. The study sites were alpine areas and urban areas (inland or coastal cities) across central Japan, in the easternmost part of Asia where atmospheric pollutants are transported from mainland Asia. The mean PAH concentrations of pine needles and mosses were 198.9 ± 184.2 ng g^-1 dry weight (dw) and 131.8 ± 60.7 ng g^-1 dw (mean ± SD), respectively. Pine needles preferentially accumulated PAHs with low molecular weights (LMW PAHs) and exhibited large differences in both PAH concentration and isomer ratios between alpine and urban sites. These differences can be explained by the strong influence of LMW PAHs emitted from domestic sources, which decreased and changed during transport from urban to alpine sites due to dry/wet deposition and photodegradation. In contrast, mosses accumulated a higher ratio of PAHs with high molecular weight (HMW PAHs). A comparison of isomer ratios showed that the PAH source for alpine moss was similar to that for northern coastal cities, which are typically influenced by long-transported PAHs from East Asia. Thus, these results indicate that alpine moss can also be strongly affected by the transboundary PAHs. It is likely that the uptake characteristics of moss, alpine climate, and alpine locations far from urban areas can strengthen the influence of transboundary pollution. Based on these results, the limitations and most effective use of bioindicators of PAH pollution for preserving alpine ecosystems are discussed.