Chemical Differences in Environmental Films Collected on Surfaces with Different Hydrophilicity.

Environmental films form when airborne particles and molecular species adsorb on solid surfaces. Recent studies have characterized these films but overlook how collection methods and host-surface character (orientation, chemical functionality, or height) change the deposition process. In this work, environmental films are collected at a rural location on gold and silicon surfaces (water contact angles of ca. 57° and <1°, respectively) to determine how the different substrate changes the properties of the accumulated environmental film. Results show that gold surfaces have a homogeneous distribution of film mass across the surface, while silicon surfaces collect films with irregular patchy domains. The two surfaces also develop different surface coverages and particle number densities, and the particles' packing arrangements are quantified by analyzing nearest-neighbor distances. Computer-controlled scanning electron microscopy with energy-dispersive X-ray spectroscopy suggests that, despite morphological differences, larger (>5 μm) particles have similar elemental compositions. Minor variations are observed at smaller particle sizes (∼5 μm), which include carbon-rich particles primarily attributed to pollen or biotic activity. Chemical analysis shows the presence of nitrate and sulfate, as well as heterogeneous cation pools on the surfaces.