Development, characterization and first deployment of an improved online reactive oxygen species analyzer

• Main Authors: J. Zhou, E. A. Bruns, P. Zotter, G. Stefenelli, A. S. H. Prévôt, U. Baltensperger, I. El-Haddad, J. Dommen
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-01-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://www.atmos-meas-tech.net/11/65/2018/amt-11-65-2018.pdf
• ISSN: 1867-1381; 1867-8548

Inhalation of atmospheric particles is linked to human diseases. Reactive oxygen species (ROS) present in these atmospheric aerosols may play an important role. However, the ROS content in aerosols and their formation pathways are still largely unknown. Here, we have developed an online and offline ROS analyzer using a 2′,7′-dichlorofluorescin (DCFH) based assay. The ROS analyzer was calibrated with H₂O₂ and its sensitivity was characterized using a suite of model organic compounds. The instrument detection limit determined as 3 times the noise is 1.3 nmol L⁻¹ for offline analysis and 2 nmol m⁻³ of sampled air when the instrument is operated online at a fluorescence response time of approximately 8 min, while the offline method detection limit is 18 nmol L⁻¹. Potential interferences from gas-phase O₃ and NO₂ as well as matrix effects of particulate SO₄²⁻ and NO₃⁻ were tested, but not observed. Fe³⁺ had no influence on the ROS signal, while soluble Fe²⁺ reduced it if present at high concentrations in the extracts. Both online and offline methods were applied to identify the ROS content of different aerosol types, i.e., ambient aerosols as well as fresh and aged aerosols from wood combustion emissions. The stability of the ROS was assessed by comparing the ROS concentration measured by the same instrumentation online in situ with offline measurements. We also analyzed the evolution of ROS in specific samples by conducting the analysis after storage times of up to 4 months. The ROS were observed to decay with increasing storage duration. From their decay behavior, ROS in secondary organic aerosol (SOA) can be separated into short- and long-lived fractions. The half-life of the short-lived fraction was 1.7 ± 0.4 h, while the half-life of the long-lived fraction could not be determined with our uncertainties. All these measurements showed consistently that on average 60 ± 20 % of the ROS were very reactive and disappeared during the filter storage time. This demonstrates the importance of a fast online measurement of ROS.