Particle penetration through a 300 m inlet pipe for sampling atmospheric aerosols from a tall meteorological tower

Abstract

An aerosol inlet pipe with an internal diameter of 2.8 cm and overall length of 300 m was designed for deployment on a tall meteorological tower. During this work the transport losses of aerosol particles across the pipe were experimentally ascertained for particle diameters between 10 and 400 nm, and sampling flows between 20 and 60 l min-1. The transport losses were determined by simultaneously measuring particle number size distributions of ambient aerosol upstream and downstream of the 300 m pipe using two scanning mobility particle sizers (SMPS). At a sampling flow of 40 l min-1, the particle penetration attained a maximum of 0.97 (±0.01) for particles in the size range between 50 and 200 nm. This particle penetration decreased to 0.66 (± 0.03) for 20 nm particles, and 0.29 (±0.04) for 10 nm particles. Theoretical values for the particle penetration through the pipe were calculated based on expressions accounting for Brownian diffusion in laminar, or fully turbulent flow. In addition, computational fluid dynamics (CFD) modeling was used to estimate particle deposition inside the rectangular bends of the pipe. For the particle size range between 10 and 200 nm the calculated particle penetration efficiency agreed with experimental values within a relative uncertainty of 5%. The calibration results for the horizontally oriented test set-up are applied to provide size-dependent correction factors for the final pipe installation at the tall meteorological tower in Siberia. The work demonstrates the practical feasibility of unusually long inlet pipes for atmospheric particle sampling and encourages their deployment on tall towers, which warrants in-situ atmospheric measurements of greater representativeness than near-surface measurements. Copyright © American Association for Aerosol Research.