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1. Applications of 1,3,5-trimethoxybenzene as a derivatizing agent for quantifying free chlorine, free bromine, bromamines, and bromide in aqueous systems

   https://doi.org/10.1039/C9AY01443H  

   Dias, Ryan P. ; Schammel, Marella H. ; Reber, Keith P. ; Sivey, John D. ( January 2019 , Analytical Methods)

   Free chlorine and free bromine ( e.g. , HOCl and HOBr) are employed as disinfectants in a variety of aqueous systems, including drinking water, wastewater, ballast water, recreational waters, and cleaning products. Yet, the most widely used methods for quantifying free halogens, including those employing N , N -diethyl- p -phenylenediamine (DPD), cannot distinguish between HOCl and HOBr. Herein, we report methods for selectively quantifying free halogens in a variety of aqueous systems using 1,3,5-trimethoxybenzene (TMB). At near-neutral pH, TMB reacted on the order of seconds with HOCl, HOBr, and inorganic bromamines to yield halogenated products that were readily quantifiedmore »by liquid chromatography or, following liquid–liquid extraction, gas chromatography-mass spectrometry (GC-MS). The chlorinated and brominated products of TMB were stable, and their molar concentrations were used to calculate the original concentrations of HOCl (method quantitation limit (MQL) by GC-MS = 15 nmol L −1 = 1.1 μg L −1 as Cl 2 ) and HOBr (MQL by GC-MS = 30 nmol L −1 = 2 μg L −1 as Cl 2 ), respectively. Moreover, TMB derivatization was efficacious for quantifying active halogenating agents in drinking water, pool water, chlorinated surface waters, and simulated spa waters treated with 1-bromo-3-chloro-5,5-dimethylhydantoin. TMB was also used to quantify bromide as a trace impurity in 20 nominally bromide-free reagents (following oxidation of bromide by HOCl to HOBr). Several possible interferents were tested, and iodide was identified as impeding accurate quantitation of HOCl and HOBr. Overall, compared to the DPD method, TMB can provide lower MQLs, larger linear ranges, and selectivity between HOCl and HOBr.« less
2. OH and HO₂ radical chemistry in a midlatitude forest: measurements and model comparisons

   https://doi.org/10.5194/acp-20-9209-2020  

   Lew, Michelle M. ; Rickly, Pamela S. ; Bottorff, Brandon P. ; Reidy, Emily ; Sklaveniti, Sofia ; Léonardis, Thierry ; Locoge, Nadine ; Dusanter, Sebastien ; Kundu, Shuvashish ; Wood, Ezra ; et al ( January 2020 , Atmospheric Chemistry and Physics)

   Abstract. Reactions of the hydroxyl (OH) and peroxy (HO2 and RO2) radicals playa central role in the chemistry of the atmosphere. In addition to controlling the lifetimes ofmany trace gases important to issues of global climate change, OH radical reactionsinitiate the oxidation of volatile organic compounds (VOCs) which can lead to the production ofozone and secondary organic aerosols in the atmosphere. Previous measurements of these radicalsin forest environments characterized by high mixing ratios of isoprene and low mixing ratios ofnitrogen oxides (NOx) (typically less than 1–2 ppb) have shown seriousdiscrepancies with modeled concentrations. These results bring into question our understanding ofthe atmosphericmore »chemistry of isoprene and other biogenic VOCs under low NOxconditions. During the summer of 2015, OH and HO2 radical concentrations, as well as totalOH reactivity, were measured using laser-induced fluorescence–fluorescence assay by gasexpansion (LIF-FAGE) techniques as part of the Indiana Radical Reactivity and Ozone productioN InterComparison (IRRONIC). This campaign took place in a forested area near Indiana University's Bloomington campus which is characterized by high mixing ratios of isoprene (average daily maximum ofapproximately 4 ppb at 28 ∘C) and low mixing ratios of NO (diurnal averageof approximately 170 ppt). Supporting measurements of photolysis rates, VOCs,NOx, and other species were used to constrain a zero-dimensional box model basedon the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM 3.2),including versions of the Leuven isoprene mechanism (LIM1) for HOx regeneration(RACM2-LIM1 and MCM 3.3.1). Using an OH chemical scavenger technique, the study revealed thepresence of an interference with the LIF-FAGE measurements of OH that increased with bothambient concentrations of ozone and temperature with an average daytime maximum equivalentOH concentration of approximately 5×106 cm−3. Subtraction of theinterference resulted in measured OH concentrations of approximately4×106 cm−3 (average daytime maximum) that were in better agreement with modelpredictions although the models underestimated the measurements in the evening. The addition ofversions of the LIM1 mechanism increased the base RACM2 and MCM 3.2 modeled OH concentrationsby approximately 20 % and 13 %, respectively, with the RACM2-LIM1 mechanism providing thebest agreement with the measured concentrations, predicting maximum daily OH concentrationsto within 30 % of the measured concentrations. Measurements of HO2 concentrationsduring the campaign (approximately a 1×109 cm−3 average daytime maximum)included a fraction of isoprene-based peroxy radicals(HO2*=HO2+αRO2) and were found to agree with modelpredictions to within 10 %–30 %. On average, the measured reactivity was consistent with thatcalculated from measured OH sinks to within 20 %, with modeled oxidation productsaccounting for the missing reactivity, however significant missing reactivity (approximately40 % of the total measured reactivity) was observed on some days.« less
3. Synergistic Multiphase Chemistry of Isoprene Hydroxy Hydroperoxides (ISOPOOH) with Sulfur Dioxide in Acidic Sulfate Aerosols Leading to Secondary Inorganic and Organic Aerosol Formation

   Zhang, Yue ; Yan, Yan ; Chen, Yuzhi ; Armstrong, Cazimir ; Zhang, Zhenfa ; Gold, Avram ; Turpin, Barbara ; Surratt, Jason ( October 2021 , 2021 AAAR 39th Annual Conference)

   In order to examine the reaction products, kinetics, and implications of ISOPOOH with aqueous sulfite, ammonium bisulfate particles were injected into the UNC 10‐m3 indoor environmental chamber under humid (i.e., 72% RH) and dark conditions. After the inorganic sulfate concentration stabilized, selected concentrations of gas‐phase 1,2‐ISOPOOH were injected into the chamber, and aerosols showed a minimal mass increase. Gaseous SO2 was subsequently injected into the chamber and a significant amount of aerosol mass was produced. The gas‐phase ISOPOOH and particle‐phase species were sampled with online instruments, including a chemical ionization mass spectrometer (CIMS), an aerosol chemical speciation monitor (ACSM), amore »particle‐into‐liquid sampler (PILS) for analysis by ion chromatography analysis (IC), and filter samples were analyzed by an ultra‐performance liquid chromatography coupled to an electrospray ionization highresolution quadrupole time‐of‐flight mass spectrometry (UPLCESI‐ HR‐QTOFMS) to obtain offline molecular‐level information. Results show that a significant amount of inorganic sulfate and organosulfates were formed rapidly after injecting SO2, altering the chemical and physical properties of the particles including phase state, pH, reactivity, and composition. Multifunctional C5‐organic species that were previously measured in atmospheric fine aerosol samples were also reported here as reaction products, including 2‐methyletrols and 2‐methyltetrol sulfates that were previously thought to be only produced from the reactive uptake of isoprene‐derived epoxydiols (IEPOX). Such results indicate that the multiphase reactions of ISOPOOH could have significant impacts on the atmospheric lifecycle of organic aerosols and sulfur, as well as the physicochemical properties of ambient particles.« less
4. LOCATER: Cleaning WiFi Connectivity Datasets for Semantic Localization

   Yiming Lin, Daokun Jiang ( January 2021 , Proceedings of the VLDB Endowment)

   This paper explores the data cleaning challenges that arise in using WiFi connectivity data to locate users to semantic indoor locations such as buildings, regions, rooms. WiFi connectivity data consists of sporadic connections between devices and nearby WiFi access points (APs), each of which may cover a relatively large area within a building. Our system, entitled semantic LOCATion cleanER (LOCATER), postulates semantic localization as a series of data cleaning tasks - first, it treats the problem of determining the AP to which a device is connected between any two of its connection events as a missing value detection and repairmore »problem. It then associates the device with the semantic subregion (e.g., a conference room in the region) by postulating it as a location disambiguation problem. LOCATER uses a bootstrapping semi-supervised learning method for coarse localization and a probabilistic method to achieve finer localization. The paper shows that LOCATER can achieve significantly high accuracy at both the coarse and fine levels.« less
5. Importance of biogenic volatile organic compounds to acyl peroxy nitrates (APN) production in the southeastern US during SOAS 2013

   https://doi.org/10.5194/acp-19-1867-2019  

   Toma, Shino ; Bertman, Steve ; Groff, Christopher ; Xiong, Fulizi ; Shepson, Paul B. ; Romer, Paul ; Duffey, Kaitlin ; Wooldridge, Paul ; Cohen, Ronald ; Baumann, Karsten ; et al ( January 2019 , Atmospheric Chemistry and Physics)

   Abstract. Gas-phase atmospheric concentrations of peroxyacetyl nitrate (PAN),peroxypropionyl nitrate (PPN), and peroxymethacryloyl nitrate (MPAN) weremeasured on the ground using a gas chromatograph electron capture detector(GC-ECD) during the Southern Oxidants and Aerosols Study (SOAS) 2013 campaign(1 June to 15 July 2013) in Centreville, Alabama, in order to studybiosphere–atmosphere interactions. Average levels of PAN, PPN, and MPAN were169, 5, and 9 pptv, respectively, and the sum accounts for an average of16 % of NO_y during the daytime (10:00 to 16:00 localtime). Higher concentrations were seen on average in air that came to thesite from the urban NO_x sources to the north. PAN levelswere themore »lowest observed in ground measurements over the past two decades inthe southeastern US. A multiple regression analysis indicates that biogenicvolatile organic compounds (VOCs) account for 66 % of PAN formationduring this study. Comparison of this value with a 0-D model simulation ofperoxyacetyl radical production indicates that at least 50 % of PANformation is due to isoprene oxidation. MPAN has a statistical correlationwith isoprene hydroxynitrates (IN). Organic aerosol mass increases withgas-phase MPAN and IN concentrations, but the mass of organic nitrates inparticles is largely unrelated to MPAN.

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