Vertical profile of particulate matter: A review of techniques and methods

Vertical profile of PM concentration is crucial for understanding PM dispersion and improving air quality forecasts. The paper presents a critical review of different techniques, viz., meteorological tower/buildings, aircraft, balloons, remote sensing and UAVs (Unmanned Aerial Vehicles) used in the past to get the vertical profile of PM. Irrespective of the technique used, the PM concentration was found to be heavily influenced by meteorology, particularly temperature inversions above the ground. Low-altitude vertical profile studies used UAV (<1000 m) and meteorological towers and buildings (<= 400 m). The studies with the objective of understanding long range transport of PM and climate change associated with PM in the atmosphere used remote sensing, aircraft and balloons to get the vertical profiles. Vertical concentrations were found to be decreasing, increasing or a combination of both depending upon the site-specific factors. Many of the high-altitude studies reported stratified layers of higher PM concentration several kms above the ground level. Chemical compositions of PM were obtained by using buildings at lower altitudes and aircraft at higher altitudes which provided information on the source of the pollution. The applicability of each technique has been discussed, highlighting their limitations and specific applications.