Seiya Nagao

Trace elements bound to PM_2.5 constitute crucial factors increasing human health risks. To optimize health-oriented air quality management strategies for industrial cities, this study monitored major trace elements in PM_2.5 in Wuhan, China, from June 2023 to May 2024. During the study period, the mean concentration of trace elements was 3290 ± 2270 ng/m³, comprising 93.9% crustal elements and 6.1% heavy metals. The positive matrix factorization model identified fugitive dust as the primary source of trace elements, with a mean contribution of 35.6%, followed by traffic emissions (21.8%), industrial emissions (19.1%), biomass and waste incineration (12.3%), and coal combustion (11.1%). Health risk assessment revealed that the cumulative non-carcinogenic and carcinogenic risks of trace elements via inhalation exposure exceeded acceptable levels for both local children and adults, with Mn, As, and Cr as key risk factors. Although coal combustion contributed less to trace element concentrations than other sources, it was the largest contributor to non-carcinogenic and carcinogenic risks, followed by fugitive dust and traffic emissions. These results suggest that trace element pollution control in Wuhan should prioritize reducing coal combustion emissions, while emphasizing the critical importance of sustained traffic regulation and fugitive dust suppression to improve air quality and protect public health.

To clarify the pollution characteristics of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) in the East Asian monsoon region under different atmospheric environments and to assess their potential influences on receptor areas, this study selected two background monitoring stations with different environments in Shimane Prefecture, Japan: a marine station (MB) and a forest station (SF). PM₂.₅ samples were simultaneously collected using a high-volume sampler during the summer and winter of 2022–2023, and ten PAHs and three NPAHs were quantified using HPLC. The concentrations of PAHs and NPAHs at MB and SF exhibited significant seasonal variations in 2022 (winter > summer). However, in 2023, a clear seasonal difference was observed only at MB. Isomer ratio analysis of PAHs at both stations indicated that traffic emissions and biomass or coal combustion were major contributors. Seasonal variations in the [2-NFR]/[1-NP] ratio indicated that, while high ratios at MB and SF during summer were mainly associated with local photochemical formation, low ratios in winter reflected long-range transportation of combustion-derived PAHs and NPAHs from the Asian continent. Incremental lifetime cancer risk values (10⁻⁷ to 10⁻¹¹) indicated that even at background stations, the atmospheric environment poses certain health risks. This first comparative investigation of PAHs and NPAHs at two distinct background stations in Shimane again highlights the importance of international cooperation among East Asian countries for effective air pollution control.

The East China Sea (ECS) is one of the largest marginal seas in the world with high primary productivity and a large area of low dissolved oxygen. This study observed the low‐oxygen bottom water on the outer‐edge shelf of ECS in summer seasons of 2018–2020. The contributions of various water masses to low‐oxygen waters were quantified, and the interaction between low‐oxygen water and Kuroshio water was validated by a mixing model using heavy rare earth elements (HREEs) together with potential temperature, and salinity. For further reliability verification, tracers such as δ³⁴S and ²²⁶Ra were additionally utilized to avoid the non‐conservative processes on the shelf area. The low‐oxygen water on the shelf was clarified to be linked to the inner/middle shelf water, and dominated by Kuroshio Subsurface Water (KSSW, 81% ± 3%) and influenced by a non‐negligible extent of pore water (3.0% ± 0.5%). Our findings revealed the transport of low‐oxygen water from the outer‐shelf edge to the Kuroshio area, whose dissolved inorganic nitrogen and dissolved inorganic phosphorus contributions to Kuroshio were 34%–82% and 35%–83%, respectively. The nutrients of low‐oxygen water were regulated primarily by the origins of water and secondarily by organic matter remineralization (DIN: ∼17% and DIP: ∼24%). As control factors, the tide, especially spring tide largely enhanced the water contribution of pore water to low‐oxygen water by 67%, and the El Niño‐Southern Oscillation potentially affected the contributions of KSSW and mid‐shelf water to low‐oxygen water.

Asian dust (AD) events and total suspended particles (TSPs) were observed at the Kanazawa University Wajima Air Monitoring Station (KUWAMS), a Japanese background site, during the East Asian winter monsoon periods (from November to May of the following year) from 2010 to 2021. Nine kinds of polycyclic aromatic hydrocarbons (PAHs) were determined in each TSP sample. In this study, a total of 54 AD events were observed. According to the different pathways of long-range transportation, AD events were divided into AD-high events (transported at higher altitudes, approximately 4000 m) and AD-low events (transported at lower altitudes, approximately 2500 m). The TSP concentrations increased sharply in the AD events and were higher in the AD-high events (39.8 ± 19.5 μg/m³) than in the AD-low events (23.5 ± 10.5 μg/m³). AD did not have a significant effect on the ΣPAHs characteristic variation, as ΣPAHs (ΣPAHs = fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene, and indeno [1,2,3-cd]pyrene) concentrations in non-AD periods, AD-high events, and AD-low events were 543 ± 374, 404 ± 221, and 436 ± 265 pg/m³, respectively. The PAH compositions were also consistent. As a result, the TSP concentration was affected by the input air mass transported at higher altitudes from the desert region while the PAH concentration was impacted by the air mass at lower altitudes, which carried the PAHs emitted from fossil fuels and biomass combustion in northeastern China. Moreover, the health risks of PAHs were calculated with the inhalation lifetime cancer risk, which ranged from 10⁻⁶ to 10⁻⁵ ng/m³, indicating a potential carcinogenic risk at the KUWAMS during the East Asian winter monsoon periods.

Asian dust (AD) events and total suspended particle (TSP) was observed at Kanazawa University Wajima Air Monitoring Station (KUWAMS), a Japanese background site, during the East Asian winter monsoon periods (from November to May of the following year) from 2010 to 2021. Nine kinds of polycyclic aromatic hydrocarbons (PAHs) were determined in each TSP sample. In this study, a total of 54 AD events were observed. According to the different pathways of long-range transportation, AD events were divided into AD-high (transported at higher altitude, around 4000 m) and AD-low (transported at lower altitude, around 2500 m). The TSP concentrations in-creased sharply in the AD and was higher in AD-high (39.8 ± 19.5 μg/m³) than that in AD-low (23.5 ± 10.5 μg/m³). While AD didn’t have significant effect on ΣPAHs characteristic variation, as ΣPAHs concentration in non-AD periods, AD-high, AD-low were 543 ± 374, 404 ± 221, 436 ± 265 pg/m³, respectively. PAHs compositions were also consistent. As a result, TSP concentration was affected by the input air mass transported at higher altitude from the desert region while PAHs concentration was under the impact of air mass at lower altitude which carried the PAHs emitted from fossil fuels and biomass combustion in northeastern China. Moreover, the health risks of PAHs were calculated by inhalation lifetime cancer risk which ranged from 10−6 to 10−5 ng/m3, in-dicating a potential carcinogenic risk at KUWAMS during the East Asian winter monsoon period.