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.
The oxidative potential (OP) of ambient particulate matter (PM) is a commonly used metric to link the aerosol exposure to its adverse health effects. In this study, we report the first-ever real-time measurements of ambient PM2.5 OP based on a dithiothreitol (DTT) assay in Delhi, during a late winter season (February 2019). The chemical composition of PM was also measured using various collocated online instruments to identify the chemical components driving the PM2.5 OP. The hourly averaged OP during the entire campaign ranged from 0.49 -3.60 nmol/min/m 3 , with an average value of 1.57±0.7 nmol/min/m 3 . The secondary organic aerosols appear to be the major driver for the variability in the intrinsic OP of PM2.5. Although, the average PM1 mass concentration at Delhi was 13-times the average PM2.5 mass concentration reported in Illinois, USA in a similar study, it was not accompanied by a proportionate increase in the OP (average volume normalized DTT activity of PM2.5 was only 5 times of that reported in Illinois). These findings reveal substantial spatial heterogeneity in the redox properties of PM and highlight the importance of determining the PM chemical composition along with its mass concentrations for predicting the overall health impacts associated with aerosol exposure.
A pandemic such as COVID-19 can cause a sudden depletion of the worldwide supply of
respirators, forcing healthcare providers to reuse them. In this study, we
systematically evaluated dry heat treatment as a viable option for the safe
decontamination of N95 respirators (1860, 3M) before their reuse. We found that the dry
heat generated by an electric cooker (100 °C, 5% relative humidity, 50 min)
effectively inactivated Tulane virus (TV, >5.2-log
10
reduction), rotavirus
(RV, >6.6-log
10
reduction), adenovirus (AdV, >4.0-log
10
reduction), and transmissible gastroenteritis virus (TGEV, >4.7-log
10
reduction). The respirator integrity (determined on the basis of the particle filtration
efficiency and quantitative fit testing) was not compromised after 20 cycles of a 50 min
dry heat treatment. On the basis of these results, dry heat decontamination generated by
an electric cooker (e.g., rice cookers, instant pots, and ovens) could be an effective
and accessible decontamination method for the safe reuse of N95 respirators. We
recommend users measure the temperature during decontamination to ensure the respirator
temperature can be maintained at 100 °C for 50 min.
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