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

Abstract

Abstract. We developed an online instrument for measuring the oxidative potential (OP) of ambient particulate matter (PM) using the dithiothreitol (DTT) assay. The instrument uses a mist chamber (MC) to continuously collect the ambient PM2.5 in water, and then determines its DTT activity 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 =1.08, R2=0.93) and Milli-Q water (slope =1.86, R2=0.86) extracts of the PM filters, indicating a better efficiency of the 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 4-fold increase in the hourly averaged activity was observed on the night of 4 July (Independence Day fireworks display). The diurnal profile of the hourly averaged OP during weekdays showed a bimodal trend, with a sharp peak in the morning (around 07:00 LT), followed by a broader afternoon peak which plateaus around 14:00 LT and starts subsiding at night (around 19:00 LT). 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, 07:00–10:00 LT; afternoon, 10:00–15:00 LT; evening, 15:00–19:00 LT; and night, 19:00–07:00 LT) 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 vehicular (both exhaust and non-exhaust) emissions and resuspended dust, whereas secondary photochemical transformation of primary emissions appear to enhance the OP of PM during the afternoon and evening period.

Use of Dithiothreitol Assay to Evaluate the Oxidative Potential of Atmospheric Aerosols

“…Several online methods have been developed to facilitate the effort of automated aerosol collection and the subsequent DTT measurement with reduced assay time. For example, Puthussery et al used a mist chamber design to wash off the particles from the filter samples [78]. In some other studies, a particle-into-liquid sampler or liquid spot sampler has been used to directly collect aerosols into liquid [78][79][80][81].…”

“…For example, Puthussery et al used a mist chamber design to wash off the particles from the filter samples [78]. In some other studies, a particle-into-liquid sampler or liquid spot sampler has been used to directly collect aerosols into liquid [78][79][80][81]. These online sampling devices could be coupled to an online DTT measurement system.…”

Development and application of a mass closure PM<sub>2.5</sub> composition online monitoring system

“…The Ca might come from the soot produced by the inferior coal and diesel combustion in the industry (Lewis and Macias, 1980). The Fe might be related to ceramic production (Querol et al, 2007) and was thus considered to be related to industrial processes. Factor 9 was ship emissions, due to a large EV values of V .…”

Development and application of a mass closure PM<sub>2.5</sub> composition online monitoring system

“…PM2.5 (aerodynamic particles smaller than 2.5 microns in size) is currently a serious problem because its chemical components have strong harmful effects on visibility (Campbell et al, 2018), radiative forcing (Gao et al, 2017), human health (Puthussery, et al, 2018;Zhang et al, 2019), climate change (Glotfelty et al, 2014), and ecosystems (Diemoz et al, 2019;Amarloei et al, 2020). PM2.5 contains many types of components, such as trace elements, water-soluble inorganic ions, elemental carbon (EC), black carbon (BC), organic carbon (OC) or organic matter (OM), etc.…”