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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 28 May 2018

Research article | 28 May 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Development and field-testing of an online instrument for measuring the real-time oxidative potential of ambient particulate matter based on dithiothreitol assay

Joseph V. Puthussery, Chen Zhang, and Vishal Verma Joseph V. Puthussery et al.
  • Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana,61801, USA

Abstract. We developed an online instrument for measuring the oxidative potential (OP) of ambient particulate matter (PM) using dithiothreitol (DTT) assay. The instrument uses a mist chamber (MC) to continuously collect the ambient PM2.5 in water, followed by its DTT activity determination using an automated syringe pump system. The instrument was deployed at an urban site in the University of Illinois campus, and its field performance was evaluated by comparing the results with the offline DTT activity measurements of simultaneously collected PM-laden filters. The online DTT activity measurements correlated well with the offline measurements but were higher than both methanol (slope=0.86, R2=0.93) and Milli-Q water (slope=0.52, R2=0.86) extracts of the PM filters, indicating a better efficiency of MC for collecting the water-insoluble fraction of PM. The hourly measurements of ambient PM2.5 OP were obtained by running the online instrument intermittently for 50 days with minimal manual assistance. The daytime DTT activity levels were generally higher than at night. However, a four-fold increase in the hourly averaged activity was observed on the night of July 04 (Independence Day fireworks display). Diurnal profile of the hourly averaged OP during weekdays showed a bimodal trend, with a sharp peak in the morning (around 7:00AM), followed by a broader afternoon peak, which plateaus around 2:00PM, and starts subsiding at night (around 7:00PM). To investigate the association of the diurnal profile of DTT activity with the emission sources at the site, we collected time-segregated composite PM filter samples in four different time periods of the day [morning (7:00AM–10:00AM), afternoon (10:00AM–3:00PM), evening (3:00PM–7:00PM) and night (7:00PM–7:00AM)] and determined the diurnal variations in the redox active components [i.e. water soluble Cu, Fe, Mn, organic carbon, elemental carbon and water soluble organic carbon]. Based on this comparison, we attributed the daytime OP of ambient PM2.5 to the water-soluble Cu from both exhaust and non-exhaust emissions, whereas secondary particles formed by the photochemical transformation of primary emissions appear to enhance the OP of PM during the afternoon and evening period.

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Joseph V. Puthussery et al.
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Joseph V. Puthussery et al.
Joseph V. Puthussery et al.
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Short summary
Oxidative potential (OP) of ambient particulate matter (PM) has recently gained attention as an air quality metric to assess PM-induced adverse health effects. In this study, we describe the development and field-testing of a new online system, which can measure the near real-time OP of ambient PM based on dithiothreitol assay. We report an hourly averaged diurnal profile of ambient PM OP for the first time, and infer the emission sources contributing to OP at an urban location in Illinois, USA.
Oxidative potential (OP) of ambient particulate matter (PM) has recently gained attention as an...