Investigating a Liquid-Based Method for Online Organic Carbon Detection in Atmospheric Particles

A Particle-Into-Liquid Sampler (PILS) was modified and coupled with a Total Organic Carbon (TOC) Analyzer (Sievers 800T, GE Water Systems, Boulder, CO), in an attempt to measure particulate organic carbon (OC) online. The PILS droplet collection system was changed from an inertial impactor to a miniature cyclone to increase the efficiency of transferring insoluble carbonaceous aerosol to the liquid sample stream. The performance of the modified PILS was investigated with a variety of calibration aerosols through comparison with the Sunset Labs ECOC technique (NIOSH method 5040). Linear regression slopes of water-soluble organic compounds compared well with Sunset Labs measurement, agreeing to within 5%. However, a size dependence was observed when comparing insoluble carbonaceous aerosol (polystyrene latex spheres, PSL). The new method did not effectively measure insoluble particles with aerodynamic diameters greater than ∼110 nm due to inefficient analysis by the TOC. The OC measurement method was also compared with online Sunset Labs organic carbon (OC) measurements in two urban locations: Atlanta, GA, and Riverside, CA. Linear regression slopes between the PILS technique and Sunset Labs were near unity (101% to 93% ± 2 and 5%, respectively), and not statistically different from unity considering the measurement uncertainty of each method. However there was a significant (0.6 to 1.7 μgC m−3) non-zero intercept, with the Sunset Labs instrument measuring higher concentrations, possible due to the inability of the PILS to measure large, insoluble particles or positive artifacts with the non-blank corrected Sunset Labs filter-based collection method.