Application of a Fluorescent Probe for the Online Measurement of PM-Bound Reactive Oxygen Species in Chamber and Ambient Studies

Abstract

This manuscript details the application of a profluorescent nitroxide (PFN) for the online quantification of radical concentrations on particulate matter (PM) using an improved Particle Into Nitroxide Quencher (PINQ). A miniature flow-through fluorimeter developed specifically for use with the 9,10-bis(phenylethynyl)anthracene-nitroxide (BPEAnit) probe was integrated into the PINQ, along with automated gas phase corrections through periodic high efficiency particle arrestor (HEPA) filtering. The resulting instrument is capable of unattended sampling and was operated with a minimum time resolution of 2.5 min. Details of the fluorimeter design and examples of data processing are provided, and results from a chamber study of side-stream cigarette smoke and ambient monitoring campaign in Guangzhou, China are presented. Primary cigarette smoke was shown to have both short-lived (t1/2 = 27 min) and long-lived (t1/2 = indefinite) PM-bound reactive oxygen species (ROS) components which had previously only been observed in secondary organic aerosol (SOA).

Relationship between Atmospheric PM-Bound Reactive Oxygen Species, Their Half-Lives, and Regulated Pollutants: Investigation and Preliminary Model

“…However, this is only part of the picture, as the highly reactive nature of ROS causes them to dissipate over time through chemical reactions both within the particles and with the surrounding gas phase. This decay has been observed in several independent laboratory-based studies using different sources and methodologies, with distinct subsets of PM-bound ROS decaying with half-lives ranging anywhere from a few minutes, to half an hour, and to several hours, days, , or even longer . Thus, the PM-bound ROS content is not only tied to how the amount of oxygenated organics is present in a sample but also to how recently they were oxidized.…”

“…The 5 min data collected by the PINQ was subject to significant short-term variation, indicating rapid, short-term variations in PM-bound ROS concentrations in the order of minutes. This is likely due to the close proximity of the sampling site to several major roads and thus the random chance of sampling unmixed plumes from primary combustion emissions, which are known to contain ROS. , …”

“…Gas-phase contributions to the signal are corrected for by alternately sampling the total aerosol and collecting high-efficiency particle arrestor (HEPA) filtered aerosol using a valve assembly. Full details of the operation and sample processing can be found elsewhere …”

“…Full details of the operation and sample processing can be found elsewhere. 9 For this study, the valve assembly was switched every 150 s to give a final PM-bound sample resolution of 5 min with a limit of detection (LOD) of 0.01 nmol•m −3 . Liquid and aerosol flow rates were checked twice daily, with freshwater and probe supplies added each day during daily checks to ensure instrument stability.…”

“…This is because time delays between collection and analysis will inevitably lead to losses in the short-lived contribution through decay. This has motivated the development of several instruments which rapidly collect and measure PM-bound ROS online. ,− While these systems have been successful, to date, there has been no attempt to quantify the relative contributions of short- and long-lived ROS to total PM-bound ROS in the atmosphere. This paper describes efforts that aim to address this issue through the deployment of an online instrument for the rapid measurement of PM-bound ROS in an urban environment.…”