The PM_2.5/PM₁₀ ratio (PM_2.5 and PM₁₀ are defined as mass concentration of particles having aerodynamic diameter less than 2.5 and 10 µm respectively) is one of the important parameters in understanding the severity of the fine mode surface particulate matter pollution. The present study characterises PM_2.5/PM₁₀ ratio estimates from eight Indian urban sites with varying levels of urbanization. Five years (2015–2019) of collocated PM_2.5, PM₁₀, and meteorological (ambient temperature, relative humidity (RH), and wind speed) measurements are used to understand the spatial and temporal variability in the PM_2.5/PM₁₀ ratio at different scales and to investigate its relationship with meteorological parameters. Over the study sites, the seasonal mean PM_2.5/PM₁₀ ratio varied between 0.31 ± 0.08 (mean ± standard deviation) and 0.65 ± 0.13. Seasonally, the highest PM_2.5/PM₁₀ ratio was observed during winter and post-monsoon seasons. Sites in the Indo-Gangetic Plain (IGP) exhibited higher PM levels (PM_2.5 and PM₁₀) and higher PM_2.5/PM₁₀ ratios than the corresponding values recorded at other sites. The seasonal mean PM_2.5/PM₁₀ ratio estimated (over the study sites) using MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) ranged between 0.25 ± 0.08 and 0.77 ± 0.16, and exhibited consistent overestimation (when compared to values derived from measurements) during winter and pre-monsoon seasons. Grossly, the PM_2.5/PM₁₀ ratio exhibited a weak association with meteorological parameters. Interestingly, despite variations in geography, population, anthropogenic activities and PM concentrations across seasons and sites, the PM_2.5/PM₁₀ ratio showed low variability.

PM _2.5 / PM ₁₀比（PM _2.5和PM ₁₀分别定义为空气动力学直径小于2.5和10 µm的颗粒的质量浓度）是理解精细模式表面颗粒物污染严重性的重要参数之一。本研究描述了来自八个城市化程度不同的印度城市站点的PM _2.5 / PM ₁₀比率估计值。并置的PM _2.5，PM ₁₀和气象（环境温度，相对湿度（RH）和风速）的五年（2015-2019）测量用于了解PM _2.5的空间和时间变化/ PM ₁₀比值在不同尺度上的变化，并研究其与气象参数的关系。在研究地点，季节性平均PM _2.5 / PM ₁₀比在0.31±0.08（均值±标准偏差）和0.65±0.13之间变化。季节性地，在冬季和季风后季节观察到最高的PM _2.5 / PM ₁₀比。与其他站点记录的相应值相比，印度恒河平原（IGP）站点显示出更高的PM水平（PM _2.5和PM ₁₀）以及更高的PM _2.5 / PM ₁₀比。季节性平均PM _2.5 / PM ₁₀使用MERRA-2（研究和应用的现代时代回顾性分析，第2版）估算的比例（在研究地点上）介于0.25±0.08到0.77±0.16之间，并且在测量过程中表现出一致的高估（与测量得出的值相比）冬季和季风前的季节。总的来说，PM _2.5 / PM ₁₀比率与气象参数之间存在弱关联。有趣的是，尽管地理，人口，人为活动和不同季节和不同地点的PM浓度存在差异，但PM _2.5 / PM _10的比值显示出较低的变异性。