Vertical distributions of chemical components of particulate matter (PM) are essential for better understanding the climate, environmental and health effects. The steep slope from western SiChuan Basin (SCB) to eastern Tibetan Plateau (TP) provides a good platform for obtaining the gradient variations of PM chemical components. Daytime and nighttime PM1 (particulate matter smaller than 1 μm) samples were collected with the medium-volume sampler at six sites with elevation ranging from 500 m to 3500 m (Chengdu, Sanbacun, Wenchuan, Lixian, Maerkang and Hongyuan). The secondary inorganic ions and carbonaceous aerosols were the largest contributor to PM1 concentrations. The chemical components from the anthropogenic sources existed strong stratification with high concentrations inside the basin, while primary natural ions showed little discrepancy among the sites. The concentrations of primary inorganic ions from anthropogenic sources were much higher at nighttime than daytime, which was contrary to the diurnal cycle of secondary inorganic ions. Spatial heterogeneity of PM chemical components was large between basin and plateau sites, especially for NO3− and NH4+, large depending on season and daylight. The excess NH4+ concentrations existed in spring, summer and fall, while SO42− and NO3− cannot be completely neutralized by NH4+ in winter. The proportion of secondary formation in all sources significantly increased from about 10 % to 30 %–40 % with the increased elevation, while the contribution of motor vehicles declined from western SCB to eastern TP. This study will fill the scarce observations of PM chemical components at the sloped terrain and deepen the understanding of formation mechanism of heavy pollution inside the basin.

中文翻译：

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四川盆地西部至青藏高原东部陡坡地区 PM1 形成机制及来源的梯度变化


颗粒物 （PM） 化学成分的垂直分布对于更好地了解气候、环境和健康影响至关重要。四川盆地西部 （SCB） 至青藏高原东部 （TP） 的陡坡为获取 PM 化学组分的梯度变化提供了良好的平台。采用中等体积采样器在海拔 500 m 至 3500 m 的 6 个地点（成都、三巴村、汶川、丽县、马尔康和宏原）收集了白天和夜间 PM1 （小于 1 μm 的颗粒物） 样品。次级无机离子和碳质气溶胶是 PM1 浓度的最大贡献者。流域内人为来源的化学成分存在较强的分层，浓度较高，而原生天然离子在站点间差异不大。夜间人为来源的初级无机离子浓度远高于白天，这与次级无机离子的昼夜周期相反。盆地和高原地区 PM 化学成分的空间异质性较大，尤其是 NO3− 和 NH4+，随季节和日光的不同而大。过量的 NH4+ 浓度存在于春、夏和秋三季，而 SO42− 和 NO3− 在冬季不能被 NH4+ 完全中和。随着海拔的增加，所有来源中次生地层的比例从约 10 % 显著增加到 30 %–40 %，而机动车的贡献从 SCB 西部下降到高原东部。本研究将填补坡地上颗粒物化学成分的稀缺观测，加深对流域内重污染形成机制的理解。