skip to main content

Search for: All records

Creators/Authors contains: "Frank, N."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract. Short-lived highly reactive atmospheric species, such as organic peroxy radicals (RO2) and stabilized Criegee intermediates (SCIs), play an important role in controlling the oxidative removal and transformation of many natural and anthropogenic trace gases in the atmosphere. Direct speciated measurements of these components are extremely helpful for understanding their atmospheric fate and impact. We describe thedevelopment of an online method for measurements of SCIs and RO2 inlaboratory experiments using chemical derivatization and spin trappingtechniques combined with H3O+ and NH4+ chemicalionization mass spectrometry (CIMS). Using chemical derivatization agentswith low proton affinity, such as electron-poor carbonyls, we scavenge allSCIs produced frommore »a wide range of alkenes without depleting CIMS reagentions. Comparison between our measurements and results from numericmodeling, using a modified version of the Master Chemical Mechanism, showsthat the method can be used for the quantification of SCIs in laboratoryexperiments with a detection limit of 1.4×107 molecule cm−3for an integration time of 30 s with the instrumentation used in this study. Weshow that spin traps are highly reactive towards atmospheric radicals andform stable adducts with them by studying the gas-phase kinetics of thereaction of spin traps with the hydroxyl radical (OH). We also demonstrate that spin trapadducts with SCIs and RO2 can be simultaneously probed and quantified under laboratory conditions with a detection limit of 1.6×108 molecule cm−3 for an integration time of 30 s for RO2 species with the instrumentation used in this study. Spin trapping prevents radical secondary reactions and cycling, ensuring that measurements are not biased by chemical interferences, and it can be implemented for detecting RO2 species in laboratory studies and potentially in the ambient atmosphere.« less
  2. Free, publicly-accessible full text available September 1, 2022
  3. Abstract. Oxidation of organic compounds in the atmosphere produces an immenselycomplex mixture of product species, posing a challenge for both theirmeasurement in laboratory studies and their inclusion in air quality andclimate models. Mass spectrometry techniques can measure thousands of thesespecies, giving insight into these chemical processes, but the datasetsthemselves are highly complex. Data reduction techniques that groupcompounds in a chemically and kinetically meaningful way provide a route tosimplify the chemistry of these systems but have not been systematicallyinvestigated. Here we evaluate three approaches to reducing thedimensionality of oxidation systems measured in an environmental chamber:positive matrix factorization (PMF), hierarchical clustering analysismore »(HCA),and a parameterization to describe kinetics in terms of multigenerationalchemistry (gamma kinetics parameterization, GKP). The evaluation isimplemented by means of two datasets: synthetic data consisting of athree-generation oxidation system with known rate constants, generationnumbers, and chemical pathways; and the measured products of OH-initiatedoxidation of a substituted aromatic compound in a chamber experiment. Wefind that PMF accounts for changes in the average composition of allproducts during specific periods of time but does not sort compounds intogenerations or by another reproducible chemical process. HCA, on the otherhand, can identify major groups of ions and patterns of behavior andmaintains bulk chemical properties like carbon oxidation state that can beuseful for modeling. The continuum of kinetic behavior observed in a typicalchamber experiment can be parameterized by fitting species' time traces tothe GKP, which approximates the chemistry as a linear, first-order kineticsystem. The fitted parameters for each species are the number of reaction stepswith OH needed to produce the species (the generation) and an effectivekinetic rate constant that describes the formation and loss rates of thespecies. The thousands of species detected in a typical laboratory chamberexperiment can be organized into a much smaller number (10–30) of groups,each of which has a characteristic chemical composition and kinetic behavior.This quantitative relationship between chemical and kinetic characteristics,and the significant reduction in the complexity of the system, provides anapproach to understanding broad patterns of behavior in oxidation systemsand could be exploited for mechanism development and atmospheric chemistrymodeling.« less
  4. Abstract. Formaldehyde (HCHO) has been measured from space for morethan 2 decades. Owing to its short atmospheric lifetime, satellite HCHOdata are used widely as a proxy of volatile organic compounds (VOCs; pleaserefer to Appendix A for abbreviations and acronyms), providing constraintson underlying emissions and chemistry. However, satellite HCHO products fromdifferent satellite sensors using different algorithms have received littlevalidation so far. The accuracy and consistency of HCHO retrievals remainlargely unclear. Here we develop a validation platform for satellite HCHOretrievals using in situ observations from 12 aircraft campaigns with a chemicaltransport model (GEOS-Chem) as the intercomparison method. Application tothe NASA operational OMImore »HCHO product indicates negative biases (−44.5 %to −21.7 %) under high-HCHO conditions, while it indicates high biases (+66.1 % to+112.1 %) under low-HCHO conditions. Under both conditions, HCHO a priorivertical profiles are likely not the main driver of the biases. By providingquick assessment of systematic biases in satellite products over largedomains, the platform facilitates, in an iterative process, optimization ofretrieval settings and the minimization of retrieval biases. It is alsocomplementary to localized validation efforts based on ground observationsand aircraft spirals.« less