Annual Variation in Event-Scale Precipitation Δ 2 H at Barrow, Ak, Reflects Vapor Source Region

In this study, precipitation isotopic variations at Barrow, AK, USA, are linked to conditions at the moisture source region, along the transport path, and at the precipita- tion site. Seventy precipitation events between January 2009 and March 2013 were analyzed for δ2H and deuterium ex- cess. For each precipitation event, vapor source regions were identified with the hybrid single-particle Lagrangian inte- grated trajectory (HYSPLIT) air parcel tracking program in back-cast mode. The results show that the vapor source re- gion migrated annually, with the most distal (proximal) and southerly (northerly) vapor source regions occurring during the winter (summer). This may be related to equatorial ex- pansion and poleward contraction of the polar circulation cell and the extent of Arctic sea ice cover. Annual cycles of vapor source region latitude and δ2H in precipitation were in phase; depleted (enriched) δ2H values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation δ2H responded to variation in vapor source region as reflected by significant correlations betweenδ2H with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, T cool , (2) meteorological conditions at the evaporation site quantified by 2 m dew point, T d, and (3) whether the vapor transport path crossed the Brooks and/or Alaskan ranges, expressed as a Boolean variable, mt n. These three variables explained 54 % of the variance (p\u3c0.001) in precipitation δ2H with a sensitivity of −3.51 ± 0.55 ‰ ◦C−1(p\u3c0.001) to T cool, 3.23 ± 0.83 ‰ ◦C−1 (p\u3c0.001) to Td, and −32.11 ± 11.04 ‰ (p = 0.0049) depletion when mt n is true

High molecular weight SOA formation during limonene ozonolysis: insights from ultrahigh-resolution FT-ICR mass spectrometry characterization

The detailed molecular composition of laboratory generated limonene ozonolysis secondary organic aerosol (SOA) was studied using ultrahigh-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Approximately 1200 molecular formulas were identified in the SOA over the mass range of 140 to 850 Da. Four characteristic groups of high relative abundance species were observed; they indicate an array of accretion products that retain a large fraction of the limonene skeleton. The identified molecular formulas of each of the groups are related to one another by CH2, O and CH2O homologous series. The CH2 and O homologous series of the low molecular weight (MW) SOA (m/z \u3c 300) are explained with a combination of functionalization and fragmentation of radical intermediates and reactive uptake of gas-phase carbonyls. They include isomerization and elimination reactions of Criegee radicals, reactions between alkyl peroxy radicals, and scission of alkoxy radicals resulting from the Criegee radicals. The presence of compounds with 10–15 carbon atoms in the first group (e.g. C11H18O6) provides evidence for SOA formation by the reactive uptake of gas-phase carbonyls during limonene ozonolysis. The high MW compounds (m/z \u3e 300) were found to constitute a significant number fraction of the identified SOA components. The formation of high MW compounds was evaluated by molecular formula trends, fragmentation analysis of select high MW compounds and a comprehensive reaction matrix including the identified low MW SOA, hydroperoxides and Criegee radicals as building blocks. Although the formation of high MW SOA may occur via a variety of radical and non-radical reaction channels, the combined approach indicates a greater importance of the non-condensation reactions over aldol and ester condensation reaction channels. Among these hemi-acetal reactions appear to be most dominant followed by hydroperoxide and Criegee reaction channels

tert-Butyl 2-benzoyl-2-methyl­propanoate

The title compound, C15H20O3, is bent with a dihedral angle of 67.28 (9)° between the mean planes of the phenyl ring and a group encompassing the ester functionality (O=C—O—C). In the crystal, mol­ecules related by inversion symmetry are connected by weak C—H⋯O inter­actions into infinite chains. On one side of the mol­ecule there are two adjacent inter­actions between neighbouring mol­ecules involving the H atoms of methyl groups from the dimethyl groups and the O atoms of the ketone; on the other side, there are also two inter­actions to another adjacent mol­ecule involving the H atoms on the phenyl rings and the carbonyl O atoms of the ester functionality

Doctor of Philosophy

dissertationChanging climate influences water resources by altering precipitation amount, intensity, and seasonal timing, which impact water availability in terrestrial systems. Stable isotope ratios of hydrogen ( 2H 1H) and oxygen ( 18O 16O) in precipitation exhibit spatial and temporal variability that arises from variation in hydroclimatic processes, and thus trace hydroclimatic processes and change across temporal and spatial scales. In this dissertation I describe the structure and management of the open access Waterisotopes database, and use either a single or the compiled global precipitation isotope ratio dataset from the database to address questions of hydroclimatic processes and change. From analysis of a single event scale precipitation isotope dataset, I examine the present state of the Arctic hydrologic cycle in eastern Siberia, finding a potential signal of contribution of Arctic vapor during the cold season. Using the compiled, processed dataset, I identify a timeseries length limitation of approximately 5 years for calculating robust local meteoric water lines, though this guideline shifts depending on how the meteoric water line will be used. I link the spatial variability of the global dataset of meteoric water line to processes including subcloud evaporation, continental recycling, and mixed phase cloud processes, and use these process links to benchmark global climate models. My results suggest that models can improve subcloud evaporation and continental recycling processes. Finally, I used the compiled dataset to examine global multidecadal oxygen isotope change. The results suggest that precipitation isotopes record nonlocal dynamic changes, with differing hydroclimatic controls over land and ocean. This result contrasts with the isotope enabled global climate model response to climate change, which primarily reflects local changes to the water balance. The infrastructure and isotope-atmospheric process relationships developed in this dissertation have implications for interpretation of hydroclimatic processes and change, including model evaluation and interpretation of paleoclimate proxies

Tracking the moisture sources of storms at Barrow, Alaska: Seasonal variations and isotopic characteristics

Enhanced warming and increasingly ice-free Arctic seas affect Arctic precipitation. We investigate increased Arctic precipitation due to declining sea ice by relating variations in moisture sources to stable isotope compositions of precipitation. We develop a novel method for deriving moisture sources using condensation profiles derived from cloud radar measurements to formulate initial heights for air mass back trajectories. This method was used to locate the moisture sources of seventy Barrow, AK storm events between 2009 and 2013. Trajectories were calculated by NOAA's HYSPLIT, using GDAS reanalysis wind fields. We demonstrate that the moisture source migrates with season, from distal in winter to proximal in summer. Moisture source dew point exhibits a semiannual cycle, with summer and winter maxima. The spring minimum reflects the reintroduction of the Arctic source. The autumn dew point minimum reflects pre-ice ocean cooling locally. 36% of isotopic variation is statistically explained by a combination of the moisture source dew point and trajectory cooling. Transport distance and path both influence the best descriptor of isotopic composition. For local events, dew point is the stronger influence on isotopic composition, explaining 21% of variance. For distal events, the effects of trajectory cooling supersedes the moisture source signal. The orographic effect of the Alaskan and Brooks ranges account for the influence of trajectory path on isotopic composition. Local moisture events during transition seasons were slightly enriched relative to distal events. If we measure further isotopic enrichment during future transition seasons, it may reflect increased contributions from the Arctic source and thus precipitation increase. Deuterium excess reflects various combinations of latitude, sea surface temperature and relative humidity. Moisture source dew point significantly but weakly predicts storm-specific d-excess. Similar analyses can be performed across the Arctic if reanalysis data can generate reliable condensation profiles. To evaluate the efficacy of condensation profiles produced by reanalysis data, we compared the condensation profiles derived from cloud radar to those from reanalysis. On average, reanalysis produced condensation profiles with mean cloud height 1.4 times higher than those from cloud radar. The greater elevation bias translated into a more distal, and thus warmer and drier, moisture source

Low flows from drought and water use reduced total dissolved solids fluxes in the Lower Colorado River Basin between 1976 to 2008

Study area:: We evaluated the Virgin, Verde, Salt, and Gila Rivers in the Lower Colorado River Basin. The watersheds have extents in Arizona, Utah, New Mexico, US and Sonora, MX. Study focus:: We calculated trends in total dissolved solids (TDS) concentrations and fluxes with the Weighted Regressions on Time, Discharge and Season model. The modeling framework leverages daily streamflow and discrete water quality observations at specific monitoring sites. We evaluated trends for a common period (1976–2008) and the whole period of record at each monitoring site in terms of climate and anthropogenic controls. New hydrologic insights for the region:: Three rivers had persistent TDS concentrations exceeding the EPA secondary drinking water standard. All were associated with a geologic source of TDS. We observed increases and decreases in TDS concentrations at our monitoring sites, contrasting with global freshwater salinization and declining TDS concentrations in the Upper Colorado River Basin (UCRB). We attributed concentration variability to wintertime hydroclimatic forcing, with secondary influences of human water use. Reservoirs may decrease TDS concentrations by 50%. Efficiency improvements in irrigation and mining water uses may decrease TDS concentrations, while municipal growth increases TDS concentrations. We observed TDS flux declines at most monitoring sites. We attributed up to 85% of the TDS flux trend to changes in streamflow arising from drought and groundwater use. This study informs salinity dynamics in arid and aridifying locations, including the UCRB

Characterizing the secondary organic aerosol products of ozone and α-pinene using ultrahigh-resolution FT-ICR mass spectrometry

Three samples of secondary organic aerosol (SOA) were generated by reacting a-pinene and ozone in the presence of variable concentrations of hydroxyl radical scavenging cyclohexane and were characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS). The reactions were performed in the presence of different concentrations of hydroxyl radical scavenger. This provided an opportunity to examine the molecular level differences of SOA. More than 900 chemical formulas for negative ions were identified over the mass range of 100 to 820 u. The experimental reproducibility of the SOA composition and the technical reproducibility of the mass spectra were evaluated. Similar chemical formulas with similar relative abundances were observed in all three experiments. A few exceptions were particular high relative abundance signals such as m/z 357, 367 and 539, whose production efficiency increased in the presence of cyclohexane, and m/z 185, 199, 215, 231 and 261, whose production efficiency decreased in the presence of cyclohexane. In general, the composition of a-pinene SOA was only slightly influenced by the concentration of the hydroxyl radical scavenger, cyclohexane. The negative ion spectra of the SOA contained four groups of peaks over the following mass ranges: 150 \u3c n \u3c 300, 300 \u3c n \u3c 475, 475 \u3c n \u3c 600, 600 \u3c n \u3c 850. As the molecular weight increased, a variety of changes occurred. The number of individual compounds within one nominal mass increased. The range of oxygen to carbon and hydrogen ratios decreased from group I to IV. Likewise, the mean values of oxygen to carbon decreased from 0.55 to 0.42. The mean value of hydrogen to carbon, approximately 1.5, did not change with respect to molecular weight, although the range of values did decrease. The chemical formulas of groups I and II with the highest relative abundances contained 5-7 and 7-10 oxygen atoms and double bond equivalents (DBE) of 3-4 and 5-7, respectively. The chemical formulas of groups III and IV with the highest relative abundances contained 10-13 and 13-16 oxygen atoms and DBE values of 7-9 and 9-11, respectively. Several SOA accretion mechanisms cause increases of DBE of 2 or 3 and alter the O:C and H:C ratios in different ways. Observations of the oxygen content and the DBE of the SOA products suggest they resulted from a complex mixture of accretions, such as reactions of neutral molecules with hydroperoxy or criegee radicals, hemi-acetal reactions, aldol condensations or esterification reactions. To provide insight into the formation mechanisms, the molecular structures of selected group II compounds (300 \u3c n \u3c 475) were investigated using ultra-high resolution MS2

Back Trajectories for "Atmospheric Dust Deposition Varies by Season and Elevation in the Colorado Front Range, USA"

Back trajectory runs to accompany analysis of dust at sites near Boulder, CO, USA using the Stochastic Time-Inverted Lagrangian Trajectory model (STILT) run with High Resolution Rapid Refresh reanalysis data. This analysis was performed on the University of Utah's High Performance Computer 'lonepeak'. This modeling data may be used with scripts available at https://github.com/putmanannie/FrontRange-Dust; to produce the figures presented in the manuscript and supplemental information

Ultrahigh-resolution FT-ICR mass spectrometry characterization of α-pinene ozonolysis SOA

Secondary organic aerosol (SOA) of α-pinene ozonolysis with and without hydroxyl radical scavenging hexane was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Molecular formulas for more than 900 negative ions were identified over the mass range of 100–850 u. Hydroxyl radicals formed during the ozonolysis of α-pinene might be expected to alter the composition of SOA, however a majority of the molecular formulas were identified in all three experiments and with a few exceptions they had similar relative abundances. Thus, the detailed composition of SOA was only slightly influenced by the presence or absence of hydroxyl radical scavenging hexane. The negative-ion mass spectra of the SOA contained four groups of peaks with increasing mass spectral complexity corresponding to increasing molecular weight. The mean values of O:C decreased from 0.55 to 0.42 with increasing molecular weight, but the mean value of H:C, approximately 1.5, did not change with increasing molecular weight. The molecular formulas with the highest relative abundances in Groups I and II contained 5–7 and 7–10 oxygen atoms and 3–4 and 5–7 double bond equivalents, respectively. The molecular formulas with the highest relative abundances in Groups III and IV contained 10–13 and 13–16 oxygen atoms and 7–9 and 9–11 double bond equivalents, respectively. Observations of the oxygen content and the double bond equivalents of the SOA products suggest a complex mixture of accretion reaction mechanisms, without an easily confirmable dominating pathway

Molecular formula characterization of biogenic secondary organic aerosol: Descriptive statistical evaluation

The detailed molecular composition of approximately 20 laboratory generated terpene ozonolysis secondary organic aerosol (SOA) samples was studied using ultrahigh resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Individual experiments were conducted with one of four terpene SOA precursors (α-pinene, β-pinene, limonene or β-caryophyllene), varied relative humidity (RH) conditions (0%, 4%, or 30%) and the presence or absence of cyclohexane (serving as a radical scavenger). In this work, we focus on the molecular composition of the SOA experiments conducted at 4% and 30% RH without cyclohexane. In each of the experimental SOA samples, the oxygen number and the DBE values increase with increasing carbon number and three or four distinct groups (aka oligomer groups) were observed in the mass spectra. The overall bulk properties, such as the elemental ratios and the average number of double bond equivalents (DBE), of the SOA were highly similar. Despite the high number of identified species (N ≥ 1000) in each SOA sample, compounds unique to the SOA formed at either 4% or 30% RH conditions were comparatively low (\u3c 200). An exception to this was observed for the D-limonene ozonolysis SOA formed at 4% RH conditions where over 450 unique molecular formulas were observed. Due to the similarity in the bulk properties and composition of the SOA from the experiments, multivariate statistics were used to distinguish the experiments from each other. Hierarchical cluster analysis and principal component analysis was performed using the molecular formulas and their relative abundances for all of the identified species. Slight compositional differences between the experiments showed that experiments with the same terpene SOA precursor were most closely related regardless of the RH or the presence/absence of cyclohexane. Furthermore, SOA experiments with D-limonene and β-caryophyllene as precursors were clearly distinguished from β-pinene and α-pinene. When the experimental SOA composition was compared with ambient samples, we observed a high number of common monoisotopic molecular formulas for summer aerosol [63%; Mazzoleni et. al., Env. Chem. 2012] and winter cloudwater samples [60%; Zhao et. al., ACPD 2013]. However the molecular formulas identified as significant using principal components analysis, were not found consistently in both samples indicating variable SOA contributions to summer and winter ambient samples. Mazzoleni, L.R., P. Saranjampour, M.M. Dalbec, V. Samburova, B. Zielinska, A.G. Hallar, D. Lowenthal, and S. Kohl, Identification of Water-Soluble Organic Carbon in Nonurban Organic Aerosols using Ultrahigh-Resolution FT-ICR Mass Spectrometry: Organic Anions, Environmental Chemistry, Vol. 9(3) 285-297, 2012. Zhao, Y., A.G. Hallar, and L.R. Mazzoleni, Atmospheric Organic Matter in Clouds: Exact Masses and Molecular Formula Identification using Ultrahigh Resolution FT-ICR Mass Spectrometry, Atmospheric Chemistry and Physics Discussion, In Press, 2013