While it has been hypothesized that the adverse health effects associated with ambient particulate matter (PM) are due to production of hydroxyl radical (·OH), few studies have quantified ·OH production from PM. Here we report the amounts of ·OH produced from ambient fine particles (PM 2.5 ) collected in northern California and extracted in a cell-free surrogate lung fluid (SLF). On average, the extracted particles produced 470 nmol ·OH mg −1 -PM 2.5 during our 15-month collection period. There was a clear seasonal pattern in the efficiency with which particles generated ·OH, with highest production during spring and summer and lowest during winter. In addition, nighttime PM was typically more efficient than daytime PM at generating ·OH. Transition metals played the dominant role in ·OH production: on average (± σ), the addition of desferoxamine (a chelator that prevents metals from forming ·OH) to the SLF removed (90 ± 5) % of ·OH generation. Furthermore, based on the concentrations of Fe in the PM 2.5 SLF extracts, and the measured yield of ·OH as a function of Fe concentration, dissolved iron can account for the majority of ·OH produced in most of our PM 2.5 extracts.
The Sunset Laboratory Carbon Aerosol Analysis Lab Instrument is widely used for thermal-optical analysis (TOA) of ambient particulate matter samples to measure total carbon (TC), organic carbon (OC), and elemental carbon (EC), and often thermal subfractions of OC and EC. TOA operating protocols include a series of plateau temperatures at which the thermal sub-fractions evolve. The temperatures have conventionally been measured by a sensor located in the sample oven but away from the filter sample. However, the TOA protocol used by the Interagency Monitoring of Protected Visual Environments (IMPROVE) network and recently adopted by the U.S. Environmental Protection Agency (EPA) Speciation Trends Network (STN) and Chemical Speciation Network (CSN) specify temperatures to be achieved at the filter. Our goal was to develop a simple calibration method to obtain the target filter temperatures in a Sunset Instrument. This method showed good agreement with the IMPROVE/STN/CSN method and has the advantages of not damaging oven components and of providing a direct comparison of sample oven sensor and filter temperatures at the TOA protocol-specified temperatures. Calibrations performed on four Sunset Instruments yielded different sensor/filter temperature relationships. Ambient PM 2.5 samples analyzed using IMPROVE A temperatures at the oven sensor compared to IMPROVE A temperatures at the filter yielded statistically insignificant differences for TC, OC, and EC but statistically Address correspondence to Ann M. Dillner, Crocker Nuclear Laboratory, University of California-Davis, 1 Shields Ave., Davis, CA 95614, USA. E-mail: amdillner@ucdavis.edu significant differences for the carbon sub-fraction concentrations. Temperature calibrations should be performed on each Sunset Instrument to ensure comparability in the carbon sub-fractions being reported, and a simple method has been provided for performing these calibrations.
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