Identification of Airborne Particle Types and Sources at a California School Using Electron Microscopy

• Published in: Atmosphere Vol. 14; no. 11; p. 1702
• Main Authors: Wagner, Jeff, Castorina, Rosemary, Kumagai, Kazukiyo, Thompson, McKenna, Sugrue, Rebecca, Noth, Elizabeth M., Bradman, Asa, Hurley, Susan
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.11.2023
• Subjects: aerosol chemical composition; aerosol morphology; Aerosols; Agglomerates; Air cleaners; Air pollution; Air quality; Aluminosilicates; Aluminum silicates; Asthma; Automation; Black carbon; Calcium; Chlorine; Chlorine compounds; Classrooms; Combustion; Contamination; Detection limits; Droplets; Electron microscopy; Emission control equipment; Environmental aspects; Fog; Fog droplets; HVAC; Identification and classification; Low temperature; low-cost sensors; Metal particles; Metals; Morphology; Outdoor air quality; Particle size; Particles; Particulate emissions; Particulate matter; passive sampling; Salt; Salt particles; Sample contamination; Samplers; Scanning electron microscopy; Schools; Secondary aerosols; Sensors; Sodium; Sodium chloride; Sodium salts; Software; Sulfur; Sulphur; Suspended particulate matter; United States; Water droplets; Water drops; United States; United States > US; California
• DOI: 10.3390/atmos14111702
• ISSN: 2073-4433

We conducted a pilot study to investigate air quality indoors in two classrooms and outdoors on the school grounds in a California community with historically high PM2.5 (fine particulate matter, diameter < 2.5 μm). We used computer-controlled scanning electron microscopy of passive samples to identify major PM types, which were used to help interpret continuous PM2.5 and black carbon sensor data. The five major PM types were sodium salt particles with sulfur, calcium, or chlorine; aluminosilicate dusts; carbonaceous combustion agglomerates; biogenic particles; and metal-rich particles. Based on morphological evidence of water droplets, the salt particles are hypothesized to be secondary aerosols formed via the reaction of sodium chloride fog droplets with sulfur from regional sources. The carbonaceous agglomerates had unusual morphologies consistent with low-temperature combustion and smoke from open-burning activities observed nearby. The passive PM sampler and continuous sensor results indicated lower concentrations in the classroom equipped with an air cleaner. Passive samples collected in one classroom exhibited enhanced PM10–2.5 crustal particles and PM2.5 metal particles, suggesting a potential local PM source in that room. Future study designs that enable longer passive sampling times would reduce detection limits and sample contamination concerns. The determination of major airborne particle types in a given environment makes this technique a useful and unique community exposure assessment tool, even in these limited-duration (48 h) deployments.