Atmospheric stratification dynamics of size-segregated urban particulate matter in the mixed layer using a...

This study characterizes the vertical stratification dynamics of size-segregated particulate matter (PM) within the urban mixing layer of Santiago, Chile, using a portable aerosol spectrometer and meteorological sensors mounted on an unmanned aerial vehicle (UAV). Vertical profiles of temperature, relative humidity, pressure, and 24 PM size fractions were obtained at altitudes up to 300 m during morning, midday, afternoon, and evening periods on days with elevated pollution levels. The objective was to identify atmospheric stability zones and assess their influence on the vertical distribution of PM of different diameter (Dp) throughout the day. The aerosol size distribution revealed two dominant modes: an accumulation mode (0.25 μm < Dp < 1 μm; PM₁) and a coarse mode (1 μm < Dp < 10 μm; PM_1-10). Coarse-mode particles were strongly affected by stability layers, particularly during morning and evening hours, resulting in near-surface concentration increases by factors of two to three. In contrast, PM₁ exhibited vertically homogeneous profiles, indicating limited sensitivity to stratification within the first 300 m above ground level. This methodology demonstrates the capability of UAV-based platforms to capture high-resolution vertical aerosol data under urban conditions. While UAV operations in urban areas face regulatory constraints, the deployment of lighter, low-cost sensors on compact platforms offers a practical alternative for future vertical monitoring. Such data is valuable for verifying atmospheric dispersion models, characterizing extreme pollution events, and developing extended monitoring campaigns with improved spatial and temporal resolution in stratified urban environments.