Activity-based CRISPR scanning uncovers allostery in DNA methylation maintenance machinery.

Allostery enables dynamic control of protein function. A paradigmatic example is the tightly orchestrated process of DNA methylation maintenance. Despite the fundamental importance of allosteric sites, their identification remains highly challenging. Here, we perform CRISPR scanning on the essential maintenance methylation machinery-DNMT1 and its partner UHRF1-with the activity-based inhibitor decitabine to uncover allosteric mechanisms regulating DNMT1. In contrast to non-covalent DNMT1 inhibition, activity-based selection implicates numerous regions outside the catalytic domain in DNMT1 function. Through computational analyses, we identify putative mutational hotspots in DNMT1 distal from the active site that encompass mutations spanning a multi-domain autoinhibitory interface and the uncharacterized BAH2 domain. We biochemically characterize these mutations as gain-of-function, exhibiting increased DNMT1 activity. Extrapolating our analysis to UHRF1, we discern putative gain-of-function mutations in multiple domains, including key residues across the autoinhibitory TTD-PBR interface. Collectively, our study highlights the utility of activity-based CRISPR scanning for nominating candidate allosteric sites, and more broadly, introduces new analytical tools that further refine the CRISPR scanning framework.

Collection of Nitrogen Dioxide for Nitrogen and Oxygen Isotope Determination─Laboratory and Environmental Chamber Evaluation.

The family of atmospheric oxides of nitrogen, NOy (e.g., nitrogen oxides (NOx) + nitric acid (HNO3) + nitrous acid (HONO) + peroxyacetyl nitrate (PAN) + particulate nitrate (pNO3-) + other), have an influential role in atmospheric chemistry, climate, and the environment. The nitrogen (δ15N) and oxygen (δ18O and Δ17O) stable isotopes of NOy are novel tools for potentially tracking emission sources and quantifying oxidation chemistry. However, there is a lack of well-established methods, particularly for speciated gas-phase components of NOy, to accurately quantify δ15N, δ18O, and Δ17O. This work presents controlled laboratory experiments and complex chamber α-pinene/NOx oxidation experiments of a sampling apparatus constructed for the simultaneous capture of multiple NOy species for isotope analysis using a series of coated denuders, with a focus on nitrogen dioxide (NO2•). The laboratory tests indicate complete NO2• capture for the targeted concentration of 15 ppbv for at least 24 h collections at 10 liters per minute, with δ15N and δ18O precisions of ±1.3‰ and 1.0‰, respectively, and minimal (2.2% ± 0.1%) NO2• collection on upstream denuders utilized for the capture of HNO3 and other acidic gases. The multispecies NOy collection system showed excellent concentration correlations with online instrumentation for both HNO3 and NO2• and isotope reproducibility of ±1.7‰, ±1.8‰, and ±0.7‰ for δ15N, δ18O, and Δ17O, respectively, for replicate experiments and highly time-resolved collections. This work demonstrates a new method that can enable the simultaneous collection of HNO3 and NO2• for accurate quantification of concentration and isotopic composition.

Grain-size distribution dataset of supercritical flow sediments from a Gilbert-type delta that are associated with disaggregation bands.

This is a dataset of grain-size distribution in sub- and supercritical flow sediments of a Gilbert-type delta from an outcrop in North Germany. Thirteen samples of ca 2.5 kg were dried (at 105°C), and homogenised twice with a sample divider. A representative sample of 1-2 g was then analysed using laser diffraction. The grain-size distribution of the sand has a maximum between fine to medium sand, with a long fine fraction tail down to 0.06 µm and occasional coarse fractions (up to 1.5 mm) in some samples. Specific grain-size distributions correlate with the different sedimentary bedforms from which the samples were taken. This data is important for two reasons: Firstly, sedimentary structures formed by Froude supercritical flows are controlled by grain-size. However, few studies have provided grain-size datasets from the natural record, which often have a much wider grain-size distribution than experimentally-produced supercritical flow deposits. Secondly, the sands were deformed subsequently by disaggregation bands, a type of geological fault that only develops in porous granular materials, i.e. well-sorted, medium sand. The disaggregation bands are indicative of seismic or even aseismic, creeping movement of basement faults.

Identification of the Biosynthetic Gene Cluster for Pyracrimycin A, an Antibiotic Produced by Streptomyces sp.

Actinomycetes make a wealth of complex, structurally diverse natural products, and a key challenge is to link them to their biosynthetic gene clusters and delineate the reactions catalyzed by each of the enzymes. Here, we report the biosynthetic gene cluster for pyracrimycin A, a set of nine genes that includes a core nonribosomal peptide synthase (pymB) that utilizes serine and proline as precursors and a monooxygenase (pymC) that catalyzes Baeyer-Villiger oxidation. The cluster is similar to the one for brabantamide A; however, pyracrimycin A biosynthesis differs in that feeding experiments with isotope-labeled serine and proline suggest that a ring opening reaction takes place and a carbon is lost from serine downstream of the oxidation reaction. Based on these data, we propose a full biosynthesis pathway for pyracrimycin A.

Evaluating reporting of patient-reported outcomes in randomized controlled trials regarding inflammatory bowel disease: a methodological study.

Patient-reported outcomes (PROs) in randomized controlled trials pertaining to inflammatory bowel disease are important in identifying patients' perspective of treatment. Incompletely reported PROs within trials could misrepresent information for clinicians and may contribute to treatment which lacks accommodation of patient input. Our study evaluates completeness of reporting of PROs and risk of bias (RoB) to identify how well trialists are adhering to known resources for trials. We used MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials to identify eligible trials from 2006 to 2020 with at least 1 PRO measure related to inflammatory bowel disease. The trials were screened in duplicate using Rayyan. We then compared trial completion of reporting to the Consolidated Standards of Reporting Trials (CONSORT)-PRO adaptation, and assessed RoB using the Cochrane Collaboration RoB 2.0 tool. To measure trial and reporting characteristics, we performed bivariate regression analyses. Among a sample of 29 trials, the mean completion percentage for CONSORT-PRO was 46.77%. We found PROs as a secondary outcome had significantly lower CONSORT-PRO reporting (p<0.05). In addition, per cent completeness of reporting was significantly higher with both a 'therapy' intervention, and trials published following the development of CONSORT-PRO (p<0.05). Incomplete PRO reporting is common in trials focused on inflammatory bowel disease. This suboptimal reporting indicates the need for adherence to reporting guidelines. Trialists should use the CONSORT-PRO checklist, as endorsed by Patient-Reported Outcomes Tools: Engaging Users and Stakeholders, to assess their studies in order to enhance reporting adherence.

Engineering bio-interfaces for the direct electron transfer of Myriococcum thermophilum cellobiose dehydrogenase: Towards a mediator-less biosupercapacitor/biofuel cell hybrid.

Direct electron transfer (DET) of enzymes on electrode surfaces is highly desirable both for fundamental mechanistic studies and to achieve membrane- and mediator-less bioenergy harvesting. In this report, we describe the preparation and comprehensive structural and electrochemical characterization of a three-dimensional (3D) graphene-based carbon electrode, onto which the two-domain redox enzyme Myriococcum thermophilum cellobiose dehydrogenase (MtCDH) is immobilized. The electrode is prepared by an entirely novel method, which combines in a single step electrochemical reduction of graphene oxide (GO) and simultaneous electrodeposition of positively charged polyethylenimine (PEI), resulting in a well dispersed MtCDH surface. The resulting MtCDH bio-interface was characterized structurally in detail, optimized, and found to exhibit a DET maximum current density of 7.7 ± 0.9 µA cm-2 and a half-lifetime of 48 h for glucose oxidation, attributed to favorable MtCDH surface orientation. A dual, entirely DET-based enzymatic biofuel cell (EBFC) was constructed with a MtCDH bioanode and a Myrothecium verrucaria bilirubin oxidase (MvBOD) biocathode. The EBFC delivers a maximum power density (Pmax) of 7.6 ± 1.3 µW cm-2, an open-circuit voltage (OCV) of 0.60 V, and an operational lifetime over seven days, which exceeds most reported CDH based DET-type EBFCs. A biosupercapacitor/EBFC hybrid was also constructed and found to register maximum power densities 62 and 43 times higher than single glucose/air and lactose/air EBFCs, respectively. This hybrid also shows excellent operational stability with self-charging/discharging over at least 500 cycles.

Ultrafast charge transfer dynamics in 2D covalent organic frameworks/Re-complex hybrid photocatalyst.

Rhenium(I)-carbonyl-diimine complexes have emerged as promising photocatalysts for carbon dioxide reduction with covalent organic frameworks recognized as perfect sensitizers and scaffold support. Such Re complexes/covalent organic frameworks hybrid catalysts have demonstrated high carbon dioxide reduction activities but with strong excitation energy-dependence. In this paper, we rationalize this behavior by the excitation energy-dependent pathways of internal photo-induced charge transfer studied via transient optical spectroscopies and time-dependent density-functional theory calculation. Under band-edge excitation, the excited electrons are quickly injected from covalent organic frameworks moiety into catalytic RheniumI center within picosecond but followed by fast backward geminate recombination. While under excitation with high-energy photon, the injected electrons are located at high-energy levels in RheniumI centers with longer lifetime. Besides those injected electrons to RheniumI center, there still remain some long-lived electrons in covalent organic frameworks moiety which is transferred back from RheniumI. This facilitates the two-electron reaction of carbon dioxide conversion to carbon monoxide.

Alcohol use disorder: An analysis of the evidence underpinning clinical practice guidelines.

BACKGROUND: As Clinical Practice Guidelines (CPGs) provide effective guidance for providing medical care for individuals with alcohol use disorder (AUD), the evidence behind them should be robust. OBJECTIVE: Our primary objective was to critically appraise the methodological and reporting quality of systematic reviews cited within CPGs regarding the treatment of AUD. Our secondary objective was to determine how frequently Cochrane Reviews were cited as justification and to evaluate appraisals between Cochrane and non-Cochrane reviews. METHODS: We searched PubMed to identify CPGs for the treatment of AUD published between 2015 and 2021. Systematic reviews included in each CPG were evaluated using the Preferred Reporting Instrument for Systematic Reviews and Meta-Analyses (PRISMA) and a validated quality assessment tool (AMSTAR-2). Additional study characteristics were recorded. RESULTS: From the screening process, 98 systematic reviews from 6 CPGs met inclusion criteria. PRISMA adherence ranged from 72% to 85% (mean of 79%). AMSTAR-2 adherence ranged from 52% to 73% (mean of 68%). AMSTAR appraisal ratings found 32 (35.6%) critically low, 10 (11.1%) low, 35 (38.9%) moderate, and only 13 (14.4%) high systematic reviews. Cochrane systematic reviews displayed greater PRISMA (0.92 vs. 0.75: p < 0.001) and AMSTAR-2 (0.90 vs. 0.61.; p < 0.001) scores compared to the non-Cochrane studies. CONCLUSION: Systematic reviews included in CPGs for AUD treatment showed variable adherence to PRISMA and AMSTAR-2 guidelines, with almost half of the systematic reviews being critically low to low methodological quality. Given the prevalence of alcohol use disorder, methodological and reporting quality recommendations are important to strengthening evidence informing CPGs.

Ozone chemistry in western U.S. wildfire plumes.

Wildfires are a substantial but poorly quantified source of tropospheric ozone (O3). Here, to investigate the highly variable O3 chemistry in wildfire plumes, we exploit the in situ chemical characterization of western wildfires during the FIREX-AQ flight campaign and show that O3 production can be predicted as a function of experimentally constrained OH exposure, volatile organic compound (VOC) reactivity, and the fate of peroxy radicals. The O3 chemistry exhibits rapid transition in chemical regimes. Within a few daylight hours, the O3 formation substantially slows and is largely limited by the abundance of nitrogen oxides (NOx). This finding supports previous observations that O3 formation is enhanced when VOC-rich wildfire smoke mixes into NOx-rich urban plumes, thereby deteriorating urban air quality. Last, we relate O3 chemistry to the underlying fire characteristics, enabling a more accurate representation of wildfire chemistry in atmospheric models that are used to study air quality and predict climate.

Large contribution of biomass burning emissions to ozone throughout the global remote troposphere.

Ozone is the third most important anthropogenic greenhouse gas after carbon dioxide and methane but has a larger uncertainty in its radiative forcing, in part because of uncertainty in the source characteristics of ozone precursors, nitrogen oxides, and volatile organic carbon that directly affect ozone formation chemistry. Tropospheric ozone also negatively affects human and ecosystem health. Biomass burning (BB) and urban emissions are significant but uncertain sources of ozone precursors. Here, we report global-scale, in situ airborne measurements of ozone and precursor source tracers from the NASA Atmospheric Tomography mission. Measurements from the remote troposphere showed that tropospheric ozone is regularly enhanced above background in polluted air masses in all regions of the globe. Ozone enhancements in air with high BB and urban emission tracers (2.1 to 23.8 ppbv [parts per billion by volume]) were generally similar to those in BB-influenced air (2.2 to 21.0 ppbv) but larger than those in urban-influenced air (-7.7 to 6.9 ppbv). Ozone attributed to BB was 2 to 10 times higher than that from urban sources in the Southern Hemisphere and the tropical Atlantic and roughly equal to that from urban sources in the Northern Hemisphere and the tropical Pacific. Three independent global chemical transport models systematically underpredict the observed influence of BB on tropospheric ozone. Potential reasons include uncertainties in modeled BB injection heights and emission inventories, export efficiency of BB emissions to the free troposphere, and chemical mechanisms of ozone production in smoke. Accurately accounting for intermittent but large and widespread BB emissions is required to understand the global tropospheric ozone burden.

Low-Molecular-Weight Carboxylic Acids in the Southeastern U.S.: Formation, Partitioning, and Implications for Organic Aerosol Aging.

While carboxylic acids are important components in both particle and gas phases in the atmosphere, their sources and partitioning are not fully understood. In this study, we present real-time measurements of both particle- and gas-phase concentrations for five of the most common and abundant low-molecular-weight carboxylic acids (LMWCA) in a rural region in the southeastern U.S. in Fall 2016. Through comparison with secondary organic aerosol (SOA) tracers, we find that isoprene was the most important local precursor for all five LMWCA but via different pathways. We propose that monocarboxylic acids (formic and acetic acids) were mainly formed through gas-phase photochemical reactions, while dicarboxylic acids (oxalic, malonic, and succinic acids) were predominantly from aqueous processing. Unexpectedly high concentrations of particle-phase formic and acetic acids (in the form of formate and acetate, respectively) were observed and likely the components of long-range transport organic aerosol (OA), decoupled from their gas-phase counterparts. In addition, an extraordinarily strong correlation (R2 = 0.90) was observed between a particulate LMWCA and aged SOA, which we tentatively attribute to boundary layer dynamics.

Evaluation of the Infill Design on the Tensile Response of 3D Printed Polylactic Acid Polymer.

The current study explores the effects of geometrical shapes of the infills on the 3D printed polylactic acid (PLA) plastic on the tensile properties. For this purpose, by utilizing an accessible supply desktop printer, specimens of diamond, rectangular, and hexagonal infill patterns were produced using the fused filament fabrication (FFF) 3D printing technique. Additionally, solid samples were printed for comparison. The printed tensile test specimens were conducted at environmental temperature, Ta of 23 °C and crosshead speed, VC.H of 5 mm/min. Mainly, this study focuses on investigating the percentage infill with respect to the cross-sectional area of the investigated samples. The mechanical properties, i.e., modulus of toughness, ultimate tensile stress, yield stress, and percent elongation, were explored for each sample having a different geometrical infill design. The test outcomes for each pattern were systematically compared. To further validate the experimental results, a computer simulation using finite element analysis was also performed and contrasted with the experimental tensile tests. The experimental results mainly suggested a brittle behavior for solidly infilled specimen, while rectangular, diamond, and hexagonal infill patterns showed ductile-like behavior (fine size and texture of infills). This brittleness may be due to the relatively higher infill density results that led to the high bonding adhesion of the printed layers, and the size and thickness effects of the solid substrate. It made the solidly infilled specimen structure denser and brittle. Among all structures, hexagon geometrical infill showed relative improvement in the mechanical properties (highest ultimate tensile stress and modulus values 1759.4 MPa and 57.74 MPa, respectively) compared with other geometrical infills. Therefore, the geometrical infill effects play an important role in selecting the suitable mechanical property's values in industrial applications.

A Review: The Prospect of Inhaled Insulin Therapy via Vibrating Mesh Technology to Treat Diabetes.

Background: Inhaled insulin has proven to be viable and, in some aspects, a more effective alternative to subcutaneous insulin. Past and present insulin inhaler devices have not found clinical or commercial success. Insulin inhalers create a dry powder or soft mist insulin aerosol, which does not provide the required uniform particle size or aerosol volume for deep lung deposition. Methods: The primary focus of this review is to investigate the potential treatment of diabetes with a wet insulin aerosol. Vibrating mesh nebulisers allow the passive inhalation of a fine wet mist aerosol for the administration of drugs to the pulmonary system in higher volumes than other small-volume nebulisers. Results: At present, there is a significant focus on vibrating mesh nebulisers from the pharmaceutical and biomedical industries for the systemic administration of pharmaceuticals for non-traditional applications such as vaccines or the treatment of diabetes. Systemic drug administration using vibrating mesh nebulisers leads to faster-acting pharmaceuticals with a reduction in drug latency. Conclusions: Systemic conditions such as diabetes, require the innovative development of custom vibrating mesh devices to provide the desired flow rates and droplet size for effective inhaled insulin administration.

Correction: Gold-carbonyl group interactions in the electrochemistry of anthraquinone thiols self-assembled on Au(111)-surfaces.

[This corrects the article DOI: 10.1039/C9SC00061E.].

Interaction Between the a3 Region of Factor VIII and the TIL'E' Domains of the von Willebrand Factor.

The von Willebrand factor (VWF) and coagulation factor VIII (FVIII) are intricately involved in hemostasis. A tight, noncovalent complex between VWF and FVIII prolongs the half-life of FVIII in plasma, and failure to form this complex leads to rapid clearance of FVIII and bleeding diatheses such as hemophilia A and von Willebrand disease (VWD) type 2N. High-resolution insight into the complex between VWF and FVIII has so far been strikingly lacking. This is particularly the case for the flexible a3 region of FVIII, which is imperative for high-affinity binding. Here, a structural and biophysical characterization of the interaction between VWF and FVIII is presented with focus on two of the domains that have been proven pivotal for mediating the interaction, namely the a3 region of FVIII and the TIL'E' domains of VWF. Binding between the FVIII a3 region and VWF TIL'E' was here observed using NMR spectroscopy, where chemical shift changes were localized to two ß-sheet regions on the edge of TIL'E' upon FVIII a3 region binding. Isothermal titration calorimetry and NMR spectroscopy were used to characterize the interaction between FVIII and TIL'E' as well as mutants of TIL'E', which further highlights the importance of the ß-sheet region of TIL'E' for high-affinity binding. Overall, the results presented provide new insight into the role the FVIII a3 region plays for complex formation between VWF and FVIII and the ß-sheet region of TIL'E' is shown to be important for FVIII binding. Thus, the results pave the way for further high-resolution insights into this imperative complex.

Strain-Release Driven Cycloadditions for Rapid Construction of Functionalized Pyridines and Amino Alcohols.

This paper describes the development of a new variant of stereoselective strain-release driven reactions (formal homo [3 + 2] dipolar cycloadditions) which utilize housane (1) to construct functionalized amino alcohols and pyridine-substituted cyclopentanes in two to three steps from simple and easily available building blocks (nitrones and pyridine N-oxides respectively).

Gold-carbonyl group interactions in the electrochemistry of anthraquinone thiols self-assembled on Au(111)-surfaces.

New anthraquinone derivatives with either a single or two thiol groups (AQ1 and AQ2) were synthesized and immobilized in self-assembled monolayers (SAMs) on Au(111) electrodes via Au-S bonds. The resultant AQ1- and AQ2-SAMs were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which enabled mapping of the gold-carbonyl group interactions and other dynamics in the Au-S bound molecular framework. Understanding of these interactions is important for research on thiol-coated gold nanoclusters, since (I) anthraquinone derivatives are a major compound family for providing desired redox functionality in multifarious assays or devices, and (II) the gold-carbonyl interactions can strongly affect anthraquinone electrochemistry. Based on equivalent circuit analysis, it was found that there is a significant rise in polarization resistance (related to SAM structural reorganization) at potentials that can be attributed to the quinone/semi-quinone interconversion. The equivalent circuit model was validated by calculation of pseudocapacitance for quinone-to-hydroquinone interconversion, in good agreement with the values derived from CV. The EIS and CV patterns obtained provide consistent evidence for two different ECEC (i.e. proton-controlled ET steps, PCET) pathways in AQ1- and AQ2-SAMs. Notably, it was found that the formal reorganization (free) energies obtained for the elementary PCET steps are unexpectedly small for both SAMs studied. This anomaly suggests high layer rigidity and recumbent molecular orientation on gold surfaces, especially for the AQ2-SAMs. The results strongly indicate that gold-carbonyl group interactions can be controlled by favorable structural organization of anthraquinone-based molecules on gold surfaces.

Atmospheric Acetaldehyde: Importance of Air-Sea Exchange and a Missing Source in the Remote Troposphere.

We report airborne measurements of acetaldehyde (CH3CHO) during the first and second deployments of the National Aeronautics and Space Administration (NASA) Atmospheric Tomography Mission (ATom). The budget of CH3CHO is examined using the Community Atmospheric Model with chemistry (CAM-chem), with a newly-developed online air-sea exchange module. The upper limit of the global ocean net emission of CH3CHO is estimated to be 34 Tg a-1 (42 Tg a-1 if considering bubble-mediated transfer), and the ocean impacts on tropospheric CH3CHO are mostly confined to the marine boundary layer. Our analysis suggests that there is an unaccounted CH3CHO source in the remote troposphere and that organic aerosols can only provide a fraction of this missing source. We propose that peroxyacetic acid (PAA) is an ideal indicator of the rapid CH3CHO production in the remote troposphere. The higher-than-expected CH3CHO measurements represent a missing sink of hydroxyl radicals (and halogen radical) in current chemistry-climate models.

Active molecular iodine photochemistry in the Arctic.

During springtime, the Arctic atmospheric boundary layer undergoes frequent rapid depletions in ozone and gaseous elemental mercury due to reactions with halogen atoms, influencing atmospheric composition and pollutant fate. Although bromine chemistry has been shown to initiate ozone depletion events, and it has long been hypothesized that iodine chemistry may contribute, no previous measurements of molecular iodine (I2) have been reported in the Arctic. Iodine chemistry also contributes to atmospheric new particle formation and therefore cloud properties and radiative forcing. Here we present Arctic atmospheric I2 and snowpack iodide (I-) measurements, which were conducted near Utqiagvik, AK, in February 2014. Using chemical ionization mass spectrometry, I2 was observed in the atmosphere at mole ratios of 0.3-1.0 ppt, and in the snowpack interstitial air at mole ratios up to 22 ppt under natural sunlit conditions and up to 35 ppt when the snowpack surface was artificially irradiated, suggesting a photochemical production mechanism. Further, snow meltwater I- measurements showed enrichments of up to ∼1,900 times above the seawater ratio of I-/Na+, consistent with iodine activation and recycling. Modeling shows that observed I2 levels are able to significantly increase ozone depletion rates, while also producing iodine monoxide (IO) at levels recently observed in the Arctic. These results emphasize the significance of iodine chemistry and the role of snowpack photochemistry in Arctic atmospheric composition, and imply that I2 is likely a dominant source of iodine atoms in the Arctic.

Derivation of Hydroperoxyl Radical Levels at an Urban Site via Measurement of Pernitric Acid by Iodide Chemical Ionization Mass Spectrometry.

Hydroperoxyl radical (HO2) is a key species to atmospheric chemistry. At warm temperatures, the HO2 and NO2 come to a rapid steady state with pernitric acid (HO2NO2). This paper presents the derivation of HO2 from observations of HO2NO2 and NO2 in metropolitan Atlanta, US, in winter 2014 and summer 2015. HO2 was observed to have a diurnal cycle with morning concentrations suppressed by high NO from the traffic. At night, derived HO2 levels were nonzero and exhibited correlations with O3 and NO3, consistent with previous studies that ozonolysis and oxidation by NO3 are sources of nighttime HO2. Measured and model calculated HO2 were in reasonable agreement: Without the constraint of measured HO2NO2, the model reproduced HO2 with a model-to-observed ratio (M/O) of 1.27 (r = 0.54) for winter, 2014, and 0.70 (r = 0.80) for summer, 2015. Adding measured HO2NO2 as a constraint, the model predicted HO2 with M/O = 1.13 (r = 0.77) for winter 2014 and 0.90 (r = 0.97) for summer 2015. These results demonstrate the feasibility of deriving HO2 from HO2NO2 measurements in warm regions where HO2NO2 has a short lifetime.