Development and validation of an integrated Ambient Air Test Facility (AATF) for multi-instrument aerosol characterization

Abstract. The U.S. Naval Research Laboratory has developed and validated an Ambient Air Test Facility (AATF) for controlled multi-instrument aerosol generation and characterization under realistic sampling conditions. The facility consists of a 14 m flow tube system that provides turbulent (Re=40 000) outdoor ambient air flow at 2 m s−1 for testing aerosol detection and measurement systems in a controlled indoor environment. The AATF integrates 13 diagnostic instruments across four measurement categories: individual particle measurement, aerosol loading, aerosol composition, and flow characterization. Multiple aerosol generation systems enable dispersion of both liquid solutions or suspensions and dry powders, producing particle concentrations from 50 to 3000 µg m−3 and the ability to detect particles across a mean diameter range of 50 nm to 15 µm. Facility validation was conducted using multiple test chemicals including caffeine, oleic acid, phenanthrene, glycerol, tributyl phosphate, and Arizona test dust for three nominal concentration levels (low ∼ 100, medium ∼ 500, high >800 µg m−3). Aerosol concentration uniformity across the flow cross-section showed relative standard deviations below 3.5 %. Multi-instrument comparisons between redundant particle sizing systems (dual APS units, UHSAS, and Promo) demonstrated good measurement consistency, with gravimetric validation confirming total aerosol mass concentrations with a 20 % difference between the types of measurements. The Aerodyne Aerosol Mass Spectrometer correctly identified particle chemical signatures consistent with NIST fragmentation patterns for all test compounds. The facility employs shrouded probe sampling systems with isokinetic coupling to individual instruments to minimize particle losses and sampling biases across the particle size distribution. The AATF provides a repeatable and reliable aerosol generation testbed for detector development, evaluation, instrument inter-comparison, and aerosol measurement validation under controlled yet realistic ambient air conditions with controlled size distributions and total mass concentrations for a wide range of chemical aerosols.