Atmosphere

Fine particulate matter (PM_2.5) formation mechanisms in fragile highland ecosystems remain inadequately constrained, particularly regarding thermodynamic non-linearities (aerosol pH, liquid water content) and their interaction with geochemical modulation. Here, we present comprehensive year-long online measurements from Xining, Qinghai-Tibet Plateau, integrating hourly measurements of water-soluble ions, inorganic elements, and gaseous precursors with ISORROPIA-II thermodynamic modeling and ensemble machine learning. Median pH was 4.38 but exhibited two distinct pH regimes (14.8% pH < 3.0, 11.5% pH > 7.2), with acute acidification enhancing toxic metal solubility (Fe, Pb by 3-5×), and it posed distinct ecological risks. Our analysis reveals a distinct “highland mechanism triad” governing PM_2.5 dynamics: (1) winter meteorological confinement amplifying dust-catalyzed sulfate formation (SOR = 0.68); (2) spring alkaline dust buffering (pH > 7.2) that titrates NH₃ and suppresses nitrate formation (NOR < 0.10); and (3) summer photochemical oxidation constrained by chronic NH₃ limitation within an oxidant-excess regime. Random Forest achieved optimal prediction for the chemically active inorganic fraction (RMSE = 6.63 μg/m³, R² = 0.91) by learning regime-specific non-linearities, with local sensitivity analysis identifying Ca²⁺, SO₄²⁻, and Al as chemically sensitive drivers (S > 0.35) while revealing NH₃’s seasonally variable influence (rank 15 in winter, significant in summer; S > 0.28), subsequently complemented by global SHAP analysis, which further revealed NO₃⁻ as the most robust predictor (ranking 1st–2nd) and captured NH₃’s non-linear threshold effects (). Positive Matrix Factorization apportioned secondary aerosols (30.11%) within a unique alkaline–dust matrix. These findings demonstrate that highland PM_2.5 inorganic chemistry operates through fundamentally different pathways than lowland photochemical haze, with acid-induced toxic metal activation providing a new target for ecological protection in this fragile ecosystem. Seasonally adaptive mitigation is required: concurrent SO₂-NH₃ control in winter, dust suppression infrastructure in spring, and agricultural NH₃ capture in summer. This integrated framework provides a transferable methodology for air-quality management in alkaline dust-dominated, NH₃-limited highland ecosystems (>2000 m).

Although the organic fraction of PM_2.5 has been extensively studied, there is a considerable gap in understanding the organic fraction of coarse particles with diameters between 2.5 and 10 µm. We investigate the composition of coarse organic aerosol (OA) across rural, suburban, and urban areas of Switzerland. Using Aerosol Mass Spectrometer analyses of water-soluble OA extracted from collected filter samples (one entire year, 441 samples per size fraction), we identified two distinct classes of coarse OA. The first class, which constitutes 41–81% of coarse organic carbon (OC), is associated with primary biological organic carbon (PBOC). PBOC is characterized by specific marker ions (e.g., C₂H₅O₂⁺) and exhibits pronounced seasonal variation, with peak concentrations observed in the summer. This seasonal trend correlates with that of molecular markers such as arabitol and mannitol, as well as the fraction of biological particles determined by automated scanning electron microscopy coupled to energy dispersive X-ray spectroscopy of individual particles. The second class, contributing 7.9–17.8% to OC_coarse, is denoted as sulfur-containing organic carbon (SCOC) due to the presence of sulfur-containing ions such as CH₃SO₂⁺. Elevated concentrations of SCOC in urban environments near roadways suggest a strong influence from non-exhaust traffic emissions and resuspended dust. While the overall variation in coarse OC between rural and urban areas is approximately 10%, PBOC concentrations are 1.4 times higher in rural areas, whereas SCOC concentrations are 1.5 times higher in urban settings. Overall, our study shows that although OC_coarse concentrations in Switzerland are relatively consistent across site types, major water-soluble sources, particle properties and composition vary considerably geographically and seasonally.

Psoriasis is a common, chronic skin disorder that has negative impacts on patients’ quality of life, and is triggered by a combination of genetic and environmental factors. However, epidemiological evidence about the effect of air pollution on psoriasis risk is still limited and inconsistent. The generalized additive model (GAM) was applied to investigate the association between common air pollutants and daily psoriasis outpatient visits in Guangzhou, China from 2013 to 2019. The analysis focused on particulate matter with an aerodynamic diameter of less than 10 μm and 2.5 μm (PM₁₀ and PM_2.5), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂). To examine the effect modifications, stratified analyses were conducted by gender, age, and season. Population attributable fraction of psoriasis burden from ambient air pollution exposure was further calculated. A total of 145,034 psoriasis outpatient visits were included during the study period. Each 10 μg/m³ increment in PM_2.5, PM₁₀, SO₂, and NO₂ was significantly associated with an excess risk of psoriasis outpatient visits of 3.46% (95% CI: 2.53%, 4.39%), 2.51% (95% CI: 1.86%, 3.17%), 4.73% (95% CI: 2.67%, 6.82%), and 4.75% (95% CI: 3.78%, 5.73%) at lag05. Stratified analysis revealed notably stronger effects during the cold seasons. Based on the World Health Organization’s Ambient Air Quality Guidelines, PM_2.5, PM₁₀, NO₂, and SO₂ accounted for 9.08% (95% CI: 6.54%, 11.74%), 4.73% (95% CI: 3.45%, 6.06%), 8.93% (95% CI: 6.99%, 10.93%), and 0.18% (95% CI: 0.10%, 0.27%) of psoriasis outpatient visits, respectively. In conclusion, short-term air pollution exposure is an important risk factor for psoriasis outpatient visits, especially in cold seasons. PM_2.5 and NO₂ accounted for a relatively larger attributable burden among common air pollutants. Effective strategies are needed for air pollution control and prevention of psoriasis exacerbation.