Kaya Forest

Evidence for increasingly variable Palmer Drought Severity Index in the United States since 1895.

Annual and summertime trends towards increasingly variable values of the Palmer Drought Severity Index (PDSI) over a sub-decadal period (five years) were investigated within the contiguous United States between 1895 and the present. For the contiguous United States as a whole, there is a significant increasing trend in the five-year running minimum-maximum ranges for the annual PDSI (aPDSI5 yr(min|max, range)). During this time frame, the average aPDSI5 yr(min|max, range) has increased by about one full unit, indicating a substantial increase in drought variability over short time scales across the United States. The end members of the running aPDSI5 yr(min|max, range) highlight even more rapid changes in the drought index variability within the past 120 years. This increasing variability in the aPDSI5 yr(min|max, range) is driven primarily by changes taking place in the Pacific and Atlantic Ocean coastal climate regions, climate regions which collectively comprise one-third the area of the contiguous United States. Similar trends were found for the annual and summertime Palmer Hydrological Drought Index (PHDI), the Palmer Modified Drought Index (PMDI), and the Palmer Z Index (PZI). Overall, interannual drought patterns in the contiguous United States are becoming more extreme and difficult to predict, posing a challenge to agricultural and other water-resource related planning efforts.

Performance of the major semiempirical, ab initio, and DFT methods for isomerization enthalpies of linear to branched heptanes

ABSTRACT The gas phase standard state (298.15 K, 1 atm) isomerization enthalpy (ΔisomH°(g)) prediction performance of the major semiempirical, ab initio, and density functional levels of theory for environmentally relevant transformations was investigated using the linear to branched heptanes as a representative case study. The M062X density functional, MP2 (and higher) levels of Moller-Plesset perturbation theory, and the CBS and Gaussian-n composite methods are well suited for investigating the thermodynamic properties of environmentally interesting isomerizations, although the M062X functional may not be appropriate for all systems. Where large molecular systems prohibit the use of higher levels of theory, the PM6 and PDDG semiempirical methods may offer an appropriate computational cost-accuracy compromise.

Singlet–triplet excitation energies of substituted phenyl cations: a G4(MP2) and G4 theoretical study

Singlet–triplet adiabatic excitation energies (AES−T) of the parent and variously substituted phenyl cations, as well as the parent benzannelated derivatives up to anthracenyl, were calculated at the G4(MP2) and G4 levels of theory. The G4(MP2)/G4 AES−T estimates range up to 40xa0kJ/mol higher than prior density functional theory (DFT)-based predictions for these cations and suggest that AES−T and ground state multiplicity structure–property trends for phenyl cations previously proposed in the literature need to be re-assessed at higher levels of theory. In general, Hartree–Fock, DFT, and semiempirical methods do a poor job describing the singlet–triplet excitation energetics of these systems. Only modest effects of different solvation models (SMD, IEF-PCM, and C-PCM) and different polar protic through apolar aprotic solvents are evident on the calculated AES−T of the phenyl cation. Electron-donating substituents on the phenyl cation substantially lower the AES−T to an extent where some functional groups (–NH2, N(CH3)2, OCH3, and SCH3) can result in triplet ground states depending on their position relative to the cation. In contrast to the phenyl and 1- and 2-naphthyl cations, which are predicted to be ground state singlets, the three parent anthracenyl cations will be ground state triplets.

Rapidly changing climatic conditions for wine grape growing in the Okanagan Valley region of British Columbia, Canada

A statistical analysis was conducted on long-term climate records for sites bordering Okanagan Lake in the Okanagan Valley viticultural region of British Columbia, Canada. Average wine grape growing season temperatures are increasing rapidly in the area over the post-1980 period at rates upwards of 7.0±1.3°C/century. Similar increases in the average dormant season temperature are evident. These temperature changes are likely some of the most extreme observed among the worlds wine producing areas during the past few decades. Growing degree day base 10°C (GDD10) has increased by nearly 50% at some locations since the 1970s, resulting in major impacts on the corresponding climate classification for viticulture. If current climate trends continue, the southern and central portions of the region will likely enter Winkler region II within the next few decades, placing them in the same category as well-established warmer wine regions from France, Spain, Italy, and Australia. The large dormant season temperature increases over the last several decades have resulted in the area no longer being a cold season outlier when compared to most other cool-climate viticultural areas. Based on average growing season temperatures, the southern end of Okanagan Lake has moved out of the cool-climate viticultural classification and into the intermediate zone, while the central and northern regions are now at the cool/intermediate viticulture interface, similar to the historical positions of the Rhine Valley in Germany, northern Oregon in the United States, and the Loire Valley, Burgundy-Cote, Burgundy-Beaujolais, and Champagne appelations of France. The corresponding suitable grape species for the area have evolved into warmer region varietals during this time frame, having substantial economic impacts on producers. Increased temperatures are also expected to bring greater threats from agricultural pests, notably Pierces disease from the bacterium Xylella fastidiosa.

Use of the SPARC software program to calculate hydrolysis rate constants for the polymeric brominated flame retardants BC-58 and FR-1025

ABSTRACT The SPARC software program was used to estimate the acid-catalyzed, neutral, and base-catalyzed hydrolysis rate constants for the polymeric brominated flame retardants BC-58 and FR-1025. Relatively rapid hydrolysis of BC-58, producing 2,4,6-tribromophenol—and ultimately tetrabromobisphenol A—as the hydrolytically stable end products from all potential hydrolysis reactions, is expected in both environmental and biological systems with starting material hydrolytic half-lives (t1/2,hydr) ranging from less than 1 h in marine systems, several hours in cellular environments, and up to several weeks in slightly acid fresh waters. Hydrolysis of FR-1025 to give 2,3,4,5,6-pentabromobenzyl alcohol is expected to be slower (t1/2,hydr less than 0.5 years in marine systems up to several years in fresh waters) than BC-58, but is also expected to occur at rates that will contribute significantly to environmental and in vivo loadings of this compound.

Aqueous phase hydration and hydrate acidity of perfluoroalkyl and n:2 fluorotelomer aldehydes

ABSTRACT The SPARC software program and comparative density functional theory (DFT) calculations were used to investigate the aqueous phase hydration equilibrium constants (Khyd) of perfluoroalkyl aldehydes (PFAlds) and n:2 fluorotelomer aldehydes (FTAlds). Both classes are degradation products of known industrial compounds and environmental contaminants such as fluorotelomer alcohols, iodides, acrylates, phosphate esters, and other derivatives, as well as hydrofluorocarbons and hydrochlorofluorocarbons. Prior studies have generally failed to consider the hydration, and subsequent potential hydrate acidity, of these compounds, resulting in incomplete and erroneous predictions as to their environmental behavior. In the current work, DFT calculations suggest that all PFAlds will be dominantly present as the hydrated form in aqueous solution. Both SPARC and DFT calculations suggest that FTAlds will not likely be substantially hydrated in aquatic systems or in vivo. PFAld hydrates are expected to have pKa values in the range of phenols (ca. 9 to 10), whereas n:2 FTAld hydrates are expected to have pKa values ca. 2 to 3 units higher (ca. 12 to 13). In order to avoid spurious modeling predictions and a fundamental misunderstanding of their fate, the molecular and/or dissociated hydrate forms of PFAlds and FTAlds need to be explicitly considered in environmental, toxicological, and waste treatment investigations. The results of the current study will facilitate a more complete examination of the environmental fate of PFAlds and FTAlds.

Air–water partition coefficients for a suite of polycyclic aromatic and other C10 through C20 unsaturated hydrocarbons

ABSTRACT The air–water partition coefficients (Kaw) for 86 large polycyclic aromatic hydrocarbons and their unsaturated relatives were estimated using high-level G4(MP2) gas and aqueous phase calculations with the SMD, IEFPCM-UFF, and CPCM solvation models. An extensive method validation effort was undertaken which involved confirming that, via comparisons to experimental enthalpies of formation, gas-phase energies at the G4(MP2) level for the compounds of interest were at or near thermochemical accuracy. Investigations of the three solvation models using a range of neutral and ionic compounds suggested that while no clear preferential solvation model could be chosen in advance for accurate Kaw estimates of the target compounds, the employment of increasingly higher levels of theory would result in lower Kaw errors. Subsequent calculations on the polycyclic aromatic and unsaturated hydrocarbons at the G4(MP2) level revealed excellent agreement for the IEFPCM-UFF and CPCM models against limited available experimental data. The IEFPCM-UFF-G4(MP2) and CPCM-G4(MP2) solvation energy calculation approaches are anticipated to give Kaw estimates within typical experimental ranges, each having general Kaw errors of less than 0.5 log10 units. When applied to other large organic compounds, the method should allow development of a broad and reliable Kaw database for multimedia environmental modeling efforts on various contaminants.

Estimated pKa values for the environmentally relevant C1 through C8 perfluorinated sulfonic acid isomers.

ABSTRACT In order to estimate isomer-specific acidity constants (pKa) for the perfluorinated sulfonic acid (PFSA) environmental contaminants, the parameterization method 6 (PM6) pKa prediction method was extensively validated against a wide range of carbon oxyacids and related sulfonic/sulfinic acids. Excellent pKa prediction performance was observed for the carbon oxyacids using the PM6 method, but this approach was found to have a severe positive bias for sulfonic/sulfinic acids. To overcome this obstacle, a correlation was developed between non-adjusted PM6 pKa values and the corresponding experimentally obtained/estimated acidity constants for a range of representative alkyl, aryl and halogen-substituted sulfonic acids. Application of this correction to the PM6 values allows for extension of this computational method to a new acid functional group. When used to estimate isomer-specific pKa values for the C1 through C8 PFSAs, the modified PM6 approach suggests an adjusted pKa range from −5.3 to −9.0, indicating that all members of this class of well-known environmental contaminants will be effectively completely dissociated in aquatic systems.

Declining relative humidity in the Thompson River Valley near Kamloops, British Columbia, Canada: 1990-2012

Potential time trends in relative humidity (RH) were investigated for the Kamloops climate station in a semi-arid region of south-central British Columbia, Canada, between 1990 and 2012. Mean monthly 6 am and 3 pm RH at Kamloops achieve annual minima during the March to September period with substantially higher early morning RH compared to the mid-afternoon period. Significant temporal declines in RH throughout the year are evident ranging from 1.5 to 5.7%/decade. No significantly increasing temporal trends in RH were found. The findings indicate that a continuation of declining trends in RH for the study area may increase the quantity of dust and other atmospheric particulate generation from both natural and anthropogenic sources, possibly resulting in additional threats to local and regional air quality, thereby necessitating inclusion in air quality management planning and modeling efforts.

Evidence for Increasingly Variable Drought Conditions in the United States Since 1895

Annual and summertime trends towards increasingly variable values of the Palmer Drought Severity Index (PDSI) over a sub-decadal period (five years) were investigated within the contiguous United States between 1895 and the present. For the contiguous U.S. as a whole, there is a significant increasing trend in the five-year running minimum-maximum ranges for the annual PDSI (aPDSI5yr(min| max range)). During this time frame, the average aPDSI5yr(min|max range) has increased by about one full unit, indicating a substantial increase is drought variability over short time scales across the United States. The end members of the running aPDSI5yr(min|max range) highlight even more rapid changes in the drought index variability within the past 120 years. This increasing variability in the aPDSI5yr(min|max range) is driven primarily by changes taking place in the Pacific and Atlantic Ocean coastal climate regions, climate regions which collectively comprise one-third the area of the contiguous U.S. Overall, interannual drought patterns are becoming more extreme and difficult to predict, posing a challenge to agricultural and other water-resource related planning efforts.