Abstract
Abstract. 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.
Highlights
Aerosol particles have negative effects on human health (Pope and Dockery, 2006), with an estimated 3 % of cardiopulmonary and 5 % of lung cancer deaths attributable to particulate matter (PM) globally (WHO, 2013)
Reaction times of 11 and 22 min were investigated by using different reaction tube lengths in the reaction chamber and followed by measurement of the fluorescence intensity resulting from the reaction of H2O2 (Fig. 2a) and 2-hydroperoxy-2-(2hydroperoxybutan-2-ylperoxy)butane (Fig. 2b) with the working solution (WS)
The residence and response time of the sample in the instrument were measured to be approximately 19 and 8 min, respectively. The former was determined as the time from the injection of an H2O2 solution to the time the fluorescence signal started to increase, while the response time corresponds to the rise time of the fluorescence signal from 10 to 90 % of the full signal
Summary
Aerosol particles have negative effects on human health (Pope and Dockery, 2006), with an estimated 3 % of cardiopulmonary and 5 % of lung cancer deaths attributable to particulate matter (PM) globally (WHO, 2013). One of the important pathways leading to deleterious impacts on health is believed to be induced oxidative stress by the generation of reactive oxygen species (ROS), through the interaction of particulate matter with the human lung (Donaldson et al, 2002). As one of the main free radical sources generated in our body by various endogenous systems, ROS can adversely alter lipids, proteins and DNA structures, potentially leading to aging and numerous human diseases (Devasagayam et al, 2004). ROS are either produced inside the human body through generation by the inhaled PM (e.g., by transition metals) in vivo (endogenous ROS) or by transportation into the lungs on respirable
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