Continuous chemical characterization of ultrafine particulate matter (PM0.1)

Abstract

Ultrafine particles (diameter of less than 100 nm) are primary suspects for enhanced negative health effects on humans. Measuring the chemical composition and physical properties of ultrafine particles online, continuously, and accurately is particularly challenging because of their typically low mass concentration (PM0.1) and susceptibility to interference from larger particles. The few past PM0.1 chemical composition measurement studies have used cascade impactors and at least a daily temporal resolution. In this study, we perform, for the first time, high-temporal-resolution measurements of the composition and sources of PM0.1 using an aerodynamic aerosol classifier (AAC) to separate PM0.1 from larger particles, integrated with other instruments. These include a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS, for organics, sulfate, nitrate, ammonium, and chloride), a single-particle soot photometer (SP2-XR, for black carbon), and an Xact625i (for elements). Ambient PM0.1 composition measurements were conducted in a suburban area in Greece to test the system. The hourly PM0.1 levels varied from 0.4 to 1.5 µg m−3, with an average of 0.7 µg m−3. Most of the PM0.1 (45 %) was organic aerosol (OA). On average, sulfates contributed 14 %, ammonium contributed 7 %, nitrate contributed 3 %, and black carbon contributed 4 % to PM0.1. Calcium (Ca) showed a surprising high average contribution to PM0.1 (18 %). The rest of the detected elements were Fe, K, Zn, and Ti, contributing 7 % together. Source apportionment analysis showed that most of the PM0.1 OA during this summertime period was oxygenated OA (90 %), with 70 % being less oxidized and 20 % being more oxidized, while only 10 % was fresh hydrocarbon-like OA.