Quantitative Chemical Assay of Nanogram-Level PM Using Aerosol Mass Spectrometry: Characterization of Particles Collected from Uncrewed Atmospheric Measurement Platforms

Abstract. Aerosol generation techniques have expanded the utility of aerosol mass spectrometry (AMS) for offline chemical analysis of airborne particles and droplets. However, standard aerosolization techniques require relatively large liquid volumes (e.g., several milliliters) and high sample masses that limit their utility. Here we report the development and characterization of a micronebulization-AMS (MN-AMS) technique that requires as low as 10 μL of sample and can provide quantification of nanogram level of organic and inorganic substances via the usage of an isotopically labeled internal standard (³⁴SO₄²⁻). Using standard solutions, the detection limits for this technique were determined at 0.189, 0.751, and 2.19 ng for sulfate, nitrate, and organics, respectively. The analytical recoveries for these species are 104 %, 87 %, and 94 %, respectively. This MN-AMS technique was applied successfully to analyzing filter and impactor samples collected using miniature PM samplers deployable on uncrewed atmospheric measurement platforms, such as uncrewed aerial systems (UAS) and tethered balloon systems (TBS). Chemical composition of PM samples collected from a UAS field campaign conducted at the DOE Southern Great Plains (SGP) observatory was characterized. The offline MN-AMS data compared well with the in situ PM composition measured by a co-located Aerosol Chemical Speciation Monitor (ACSM). In addition, the MN-AMS and ion chromatography (IC) agreed well for measurements of sulfate and nitrate concentrations in the PM extracts. This study demonstrates the utility of combining MN-AMS with uncrewed measurement platforms to provide quantitative measurements of ambient PM composition with temporal and spatial resolution.