Development and testing of an online method to measure ambient fine particulate reactive oxygen species (ROS) based on the 2',7'-dichlorofluorescin (DCFH) assay

Abstract. An online, semi-continuous instrument to measure fine particle (PM_2.5) reactive oxygen species (ROS) was developed based on the fluorescent probe 2'7'-dichlorofluorescin (DCFH). Parameters that influence probe response were first characterized to develop an optimal method for use in a field instrument. The online method used a mist chamber scrubber to collect total (gas plus particle) ROS components (ROS_t) alternating with gas phase ROS (ROS_g) by means of an inline filter. Particle phase ROS (ROS_p) was determined by the difference between ROS_t and ROS_g. The instrument was deployed in urban Atlanta, Georgia, USA, and at a rural site during various seasons. Concentrations from the online instrument generally agreed well with those from an intensive filter measurement of ROS_p. Concentrations of the ROS_p measurements made with this instrument were lower than reported in other studies, often below the instrument's average limit of detection (0.15 nmol H₂O₂ equivalents m⁻³). Mean ROS_p concentrations were 0.26 nmol H₂O₂ equivalents m⁻³ at the Atlanta urban sites compared to 0.14 nmol H₂O₂ equivalents m⁻³ at the rural site.