Author(s)

ALFRED MICALLEF, REBECCA CARUANA, MARVIC GRIMA

Abstract

Understanding the vertical distribution of air pollutants in urban environments is essential for accurate exposure assessment, model validation and effective air quality management. This review synthesises current knowledge on vertical concentration profiles of urban pollutants, examining measurement techniques, observed patterns, controlling factors and practical applications. Traditional ground-based profiling systems, including tall towers and tethered balloons, have been complemented by advanced remote sensing technologies such as light detection and ranging technology, and unmanned aerial vehicles, enabling comprehensive characterisation of three-dimensional pollutant distributions. Primary pollutants from ground-level sources typically exhibit exponential decay with height, while secondary pollutants such as ozone display inverse gradients due to surface titration reactions. Particulate matter shows size-dependent vertical behaviour, with fine particles relatively well-mixed during convective conditions and coarse particles displaying steep gradients due to gravitational settling. Atmospheric boundary layer dynamics, urban morphology, emission source characteristics and chemical transformations fundamentally control vertical pollutant distributions. Applications include improved exposure assessment for epidemiological studies, air quality model evaluation, monitoring network optimisation and source apportionment. As cities expand vertically and climate change alters atmospheric dynamics, understanding pollutant distributions throughout the urban atmospheric column becomes increasingly critical for protecting public health and managing air quality in the growing global urban population.

Keywords

vertical concentration profiles, air pollution, concentration gradients