Aspiration ratio of a double-shrouded probe under low pressure conditions in troposphere

Abstract

Particulate matter forecasting is based on data measured at several monitoring stations fixed on the ground. The most effective way to improve forecast accuracy is to obtain measurements over a wider range. To this end, research is being conducted into data improvement methods using three-dimensional measurements over a large area using unmanned aerial vehicles (UAVs) such as drones. The environment of the troposphere, where atmospheric aerosol measurements are made using UAVs, is characterized by high velocity airflow and low pressure, and these conditions hinder representative sampling, which is the first step to accurately measure atmospheric aerosol concentrations. We evaluated the aspiration ratio using a double-shrouded probe designed to be mounted on a UAV at a high speed of up to 300 km/h and at a low pressure of 0.3 atm, the pressure in the upper troposphere. The aspiration ratio of the double-shrouded probe was predicted through simulation, and a low pressure high-speed wind tunnel that can implement an airflow velocity over 300 km/h was developed and verified through experiments. The results showed that as the pressure was lowered from 1 atm to 0.3 atm, the drag force of the air on particles decreased and the aspiration ratio of the double-shrouded probe was overestimated to some extent. However, representative sampling could be implemented with an error of 10% or less, even at speeds below 300 km/h for PM2.5. Therefore, the double-shrouded probe developed in this study enables representative sampling over much wider speed and pressure ranges than the existing sampling probes. Copyright © 2020 American Association for Aerosol Research.