An Aerosol Chemical Speciation Monitor (ACSM) for Routine Monitoring of the Composition and Mass Concentrations of Ambient Aerosol

TLDR

The study introduces the Aerosol Chemical Speciation Monitor (ACSM), an instrument that routinely measures the mass and chemical composition of non‑refractory submicron aerosol in real time. The ACSM employs aerodynamic particle focusing, high‑vacuum thermal vaporization, electron‑impact ionization, and mass spectrometry—technology derived from the Aerodyne AMS—while incorporating design changes that make it smaller, cheaper, and easier to operate, and its data are processed with the same established AMS analysis methods. Under ambient conditions the ACSM achieves sub‑0.2 μg m⁻³ detection limits for organics, sulfate, nitrate, ammonium, and chloride, operates stably for months, and produces mass concentration trends and organic aerosol component analyses that agree closely with co‑located AMS instruments.

Abstract

We present a new instrument, the Aerosol Chemical Speciation Monitor (ACSM), which routinely characterizes and monitors the mass and chemical composition of non-refractory submicron particulate matter in real time. Under ambient conditions, mass concentrations of particulate organics, sulfate, nitrate, ammonium, and chloride are obtained with a detection limit <0.2 μg/m3 for 30 min of signal averaging. The ACSM is built upon the same technology as the widely used Aerodyne Aerosol Mass Spectrometer (AMS), in which an aerodynamic particle focusing lens is combined with high vacuum thermal particle vaporization, electron impact ionization, and mass spectrometry. Modifications in the ACSM design, however, allow it to be smaller, lower cost, and simpler to operate than the AMS. The ACSM is also capable of routine stable operation for long periods of time (months). Results from a field measurement campaign in Queens, NY where the ACSM operated unattended and continuously for 8 weeks, are presented. ACSM data is analyzed with the same well-developed techniques that are used for the AMS. Trends in the ACSM mass concentrations observed during the Queens, NY study compare well with those from co-located instruments. Positive Matrix Factorization (PMF) of the ACSM organic aerosol spectra extracts two components: hydrocarbon-like organic aerosol (HOA) and oxygenated organic aerosol (OOA). The mass spectra and time trends of both components correlate well with PMF results obtained from a co-located high resolution time-of-flight AMS instrument.