UV/Vis+ photochemistry database: Structure, content and applications Noelle, Andreas; Vandaele, Ann Carine; Martin-Torres, Javier ...
Journal of Quantitative Spectroscopy & Radiative Transfer/Journal of quantitative spectroscopy & radiative transfer,
09/2020, Letnik:
253
Journal Article, Web Resource
Recenzirano
Odprti dostop
•The “science-softCon UV/Vis+ photochemistry database” contains EUV-VUV-UV–Vis-NIR spectral data.•The database also contains quantum yields and photolysis related data.•The database provides valuable ...information for astrophysics, earth and planetary sciences, medical and pharmaceutical sciences.
The “science-softCon UV/Vis+ Photochemistry Database” (www.photochemistry.org) is a large and comprehensive collection of EUV-VUV-UV–Vis-NIR spectral data and other photochemical information assembled from published peer-reviewed papers. The database contains photochemical data including absorption, fluorescence, photoelectron, and circular and linear dichroism spectra, as well as quantum yields and photolysis related data that are critically needed in many scientific disciplines.
This manuscript gives an outline regarding the structure and content of the “science-softCon UV/Vis+ Photochemistry Database”. The accurate and reliable molecular level information provided in this database is fundamental in nature and helps in proceeding further to understand photon, electron and ion induced chemistry of molecules of interest not only in spectroscopy, astrochemistry, astrophysics, Earth and planetary sciences, environmental chemistry, plasma physics, combustion chemistry but also in applied fields such as medical diagnostics, pharmaceutical sciences, biochemistry, agriculture, and catalysis. In order to illustrate this, we illustrate the use of the UV/Vis+ Photochemistry Database in four different fields of scientific endeavor.
Gas‐phase volatile organic compounds (VOCs) were measured at three vertical levels between 0.6 m and 5.4 m in the Arctic boundary layer in Barrow, Alaska, for the Ocean‐Atmosphere‐Sea Ice‐Snowpack ...(OASIS)‐2009 field campaign during March–April 2009. C4‐C8 nonmethane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs), including alcohols, aldehydes, and ketones, were quantified multiple times per hour, day and night, during the campaign using in situ fast gas chromatography‐mass spectrometry. Three canister samples were also collected daily and subsequently analyzed for C2‐C5 NMHCs. The NMHCs and aldehydes demonstrated an overall decrease in mixing ratios during the experiment, whereas acetone and 2‐butanone showed increases. Calculations of time‐integrated concentrations of Br atoms, ∫Brdt, yielded values as high as (1.34 ± 0.27) × 1014 cm−3 s during the longest observed ozone depletion event (ODE) of the campaign and were correlated with the steady state Br calculated at the site during this time. Both chlorine and bromine chemistry contributed to the large perturbations on the production and losses of VOCs. Notably, acetaldehyde, propanal, and butanal mixing ratios dropped below the detection limit of the instrument (3 parts per trillion by volume (pptv) for acetaldehyde and propanal, 2 pptv for butanal) during several ODEs due to Br chemistry. Chemical flux calculations of OVOC production and loss are consistent with localized high Cl‐atom concentrations either regionally or within a very shallow surface layer, while the deeper Arctic boundary layer provides a continuous source of precursor alkanes to maintain the OVOC mixing ratios.
Key Points
Integrated Cl and Br atom concentrations calculated from NMHC are decoupled
Strong positive correlation observed between ozone and aldehyde depletion events
Alkane‐Cl reactions play a key role in OVOC chemical fluxes in the Arctic
We demonstrate the capability of the ion mobility mass spectrometry (IMS-MS)
for molecular characterization of reactive and short-lived alkyl nitrates
(ANs) in atmospheric aerosols. We show ...significantly enhanced sensitivity
towards the intact molecules of ANs by ultimately 2 orders of magnitude
with the addition of inorganic anions such as chloride and nitrate to the
negative electrospray to promote the ion adduct formation. This approach
enables the measurement of ANs that have a low tendency to form molecular ions
on their own with an improved limit of detection in the range of 0.1 to 4.3 µM. Molecular identities of the ANs are well constrained by the
developed correlation between the collision cross section and mass-to-charge ratio,
which provides a two-dimensional separation of the -ONO2-containing
compounds on the basis of their molecular size and geometry. Structural
information of the nitrate molecules is further probed by the identification
of characteristic fragments produced from the collision-induced dissociation
of parent AN adducts. Application of the IMS-MS technique is exemplified by
the identification of hydroxy nitrates in secondary organic aerosols
produced from the photochemical oxidation of isoprene.
The chemistry–climate model ECHAM-HAMMOZ contains a detailed representation
of tropospheric and stratospheric reactive chemistry and state-of-the-art
parameterizations of aerosols using either a ...modal scheme (M7) or a bin
scheme (SALSA). This article describes and evaluates the model version
ECHAM6.3-HAM2.3-MOZ1.0 with a focus on the tropospheric gas-phase chemistry.
A 10-year model simulation was performed to test the stability of the model
and provide data for its evaluation. The comparison to observations
concentrates on the year 2008 and includes total column observations of ozone
and CO from IASI and OMI, Aura MLS observations of temperature, HNO3,
ClO, and O3 for the evaluation of polar stratospheric
processes, an ozonesonde climatology, surface ozone observations from the
TOAR database, and surface CO data from the Global Atmosphere Watch network.
Global budgets of ozone, OH, NOx, aerosols, clouds, and radiation
are analyzed and compared to the literature. ECHAM-HAMMOZ performs well in
many aspects. However, in the base simulation, lightning NOx
emissions are very low, and the impact of the heterogeneous reaction of
HNO3 on dust and sea salt aerosol is too strong. Sensitivity
simulations with increased lightning NOx or modified heterogeneous
chemistry deteriorate the comparison with observations and yield excessively
large ozone budget terms and too much OH. We hypothesize that this is an
impact of potential issues with tropical convection in the ECHAM model.
We report airborne measurements of acetaldehyde (CH3CHO) during the first and second deployments of the National Aeronautics and Space Administration 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 (42 Tg/a 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 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.
Plain Language Summary
The Earth's atmosphere and its ability to self‐regulate and cleanse itself is dependent on a complex interplay of trace chemical species, some of which are emitted from the biosphere, while others are from human activities or fires. One of these key species, acetaldehyde, was measured as part of the recent Atmospheric Tomography Mission, an aircraft (National Aeronautics and Space Administration DC‐8) experiment transecting the lengths of the Pacific and Atlantic Oceans during two seasons, measuring greenhouse gases and chemically reactive gases and particles. These measurements allow us to test our ability to model the chemical state of the atmosphere. The results indicate that the ocean is a large source of acetaldehyde and the analysis here suggests additional mechanisms that narrow the gap between observations and simulations but also reveal that an additional unexplained source or sources remain(s) in the remote free troposphere. It is critical to understand this missing carbon source because it has significant implications for understanding the cycle of oxidants which, in turn, provide for the means of removing (cleaning) trace gases including methane, an important greenhouse gas, from the atmosphere.
Key Points
Observed acetaldehyde (CH3CHO) in the remote troposphere is compatible with observed peroxyacetic acid (PAA) within uncertainties
We speculate that there is a missing CH3CHO source in the remote atmosphere and observed organic aerosols cannot explain the observed CH3CHO
The ocean is a net source of CH3CHO; the ocean biogeochemistry control on the atmospheric chemistry warrants further investigation
Polygenic risk scores (PRS) have potential to improve health care by identifying individuals that have elevated risk for common complex conditions. Use of PRS in clinical practice, however, requires ...careful assessment of the needs and capabilities of patients, providers, and health care systems. The electronic Medical Records and Genomics (eMERGE) network is conducting a collaborative study which will return PRS to 25,000 pediatric and adult participants. All participants will receive a risk report, potentially classifying them as high risk (∼2-10% per condition) for 1 or more of 10 conditions based on PRS. The study population is enriched by participants from racial and ethnic minority populations, underserved populations, and populations who experience poorer medical outcomes.
All 10 eMERGE clinical sites conducted focus groups, interviews, and/or surveys to understand educational needs among key stakeholders—participants, providers, and/or study staff. Together, these studies highlighted the need for tools that address the perceived benefit/value of PRS, types of education/support needed, accessibility, and PRS-related knowledge and understanding. Based on findings from these preliminary studies, the network harmonized training initiatives and formal/informal educational resources.
This paper summarizes eMERGE’s collective approach to assessing educational needs and developing educational approaches for primary stakeholders. It discusses challenges encountered and solutions provided.
Structure-activity relationships (SARs) are essential components of detailed chemical models, where they are employed to provide kinetic information when high-quality experimental or theoretical data ...are unavailable. Notwithstanding, there are very few types of SARs that are routinely employed to estimate reaction kinetics. Accordingly, a new temperature-dependent and site-specific technique for rate coefficient estimation is presented, based on the electrotopological state (E-state), a fundamental property that can describe the substituent effect upon each hydrogen environment in a molecule. This accounts for the electronic character of individual atoms within molecules and their respective distances from one another. This method is applied to the hydrogen abstraction reactions of OH with alkanes and haloalkanes, where it was found to perform well compared with other approaches for molecules whose rate coefficients have been measured experimentally over a broad temperature range (∼200-1500 K). To extend this comparison, an efficient software tool for batch-estimated rate coefficients has been developed. By applying this software to fully enumerated lists of halocarbons containing from one to four carbon atoms, we were able to compare predictions of >100 000 species between techniques, and although experimental coverage is sparse, we could assess the degree of consensus between these estimates. Disagreement between methods was found to increase with carbon number, and differences of up to three orders of magnitude were observed in some cases. The reasons for these discrepancies and possible solutions are discussed. In a further demonstration of the utility of the E-state approach, we show that it can also be used to calculate bond-dissociation energy (BDE), which also compares favourably with a state-of-the-art literature method. The E-state approach not only provides accurate predictions of rate coefficients, but it does so with fewer fitting parameters and by being constrained by a fundamental molecular property. From this we conject that it is less prone to overfitting and more easily expanded to unfamiliar substituents than previous SAR approaches. The efficiency and robustness with which estimates of BDE and rate coefficients are made over a wide range of conditions will be of relevance to a variety of fields including atmospheric and combustion chemistry.
Structure-activity relationships are an increasingly necessary tool to assess the reactivity of chemicals within the environment. We present a new, automated approach for estimating unknown rate coefficients based on the electrotopological state.
The products of the Cl atom initiated oxidation of diethyl ether (DEE) were investigated at atmospheric pressure over a range of temperatures (218-335 K) and O(2) partial pressures (50-700 Torr), ...both in the presence and absence of NO(x). The major products observed at 298 K and below were ethyl formate and ethyl acetate, which accounted for approximately equal to 60-80% of the reacted diethyl ether. In general, the yield of ethyl formate increased with increasing temperature, with decreasing O(2) partial pressure, and upon addition of NO to the reaction mixtures. The product yield data show that thermal decomposition reaction 3, CH(3)CH(2)-O-CH(O.)CH(3)--> CH(3)CH(2)-O-CH=O + CH(3), and reaction 6 with O(2), CH(3)CH(2)-O-CH(O.)CH(3) + O(2)--> CH(3)CH(2)-O-C(=O)CH(3) + HO(2) are competing fates of the CH(3)CH(2)-O-CH(O )CH(3) radical, with a best estimate of k3/k6 approximately equal to 6.9 x 10(24) exp(-3130/T). Thermal decomposition via C-H or C-O bond cleavage are at most minor contributors to the CH(3)CH(2)-O-CH(O.)CH(3) chemistry. The data also show that the CH(3)CH(2)-O-CH(O.)CH(3) radical is subject to a chemical activation effect. When produced from the exothermic reaction of the CH(3)CH(2)-O-CH(OO.)CH(3) radical with NO, prompt decomposition via both CH(3)- and probably H-elimination occur, with yields of about 40% and < or =15%, respectively. Finally, at temperatures slightly above ambient, evidence for a change in mechanism in the absence of NO(x), possibly due to chemistry involving the peroxy radical CH(3)CH(2)-O-CH(OO.)CH(3), is presented.
Product branching ratios for the gas-phase reactions of i-butanol, (CH3)2CHCH2OH, with OH radicals (251, 294, and 340 K) and Cl atoms (294 K) were quantified in an environmental chamber study and ...used to interpret i-butanol site-specific reactivity. i-Butyraldehyde, acetone, acetaldehyde, and formaldehyde were observed as major stable end products in both reaction systems with carbon mass balance indistinguishable from unity. Product branching ratios for OH oxidation were found to be temperature-dependent with the α, β, and γ channels changing from 34 ± 6 to 47 ± 1%, from 58 ± 6 to 37 ± 9%, and from 8 ± 1 to 16 ± 4%, respectively, between 251 and 340 K. Recommended temperature-dependent site-specific modified Arrhenius expressions for the OH reaction rate coefficient are (cm3 molecule–1 s–1): k α(T) = 8.64 × 10–18 × T 1.91exp(666/T); k β(T) = 5.15 × 10–19 × T 2.04exp(1304/T); k γ(T) = 3.20 × 10–17 × T 1.78exp(107/T); k OH(T) = 2.10 × 10–18 × T 2exp(−23/T), where k Total(T) = k α(T) + k β(T) + k γ(T) + k OH(T). The expressions were constrained using the product branching ratios measured in this study and previous total phenomenological rate coefficient measurements. The site-specific expressions compare reasonably well with recent theoretical work. It is shown that use of i-butanol would result in acetone as the dominant degradation product under most atmospheric conditions.
Relative rate studies were carried out to determine the temperature dependent rate constant ratio k 1/k 2a: CH3O· + O2 → HCHO + HO2· and CH3O· + NO2 (+M) → CH3ONO2 (+M) over the temperature range ...250–333 K in an environmental chamber at 700 Torr using Fourier transform infrared detection. Absolute rate constants k 2 were determined using laser flash photolysis/laser-induced fluorescence under the same conditions. The analogous experiments were carried out for the reactions of the perdeuterated methoxy radical (CD3O·). Absolute rate constants k 2 were in excellent agreement with the recommendations of the JPL Data Evaluation panel. The combined data (i.e., k 1/k 2 and k 2) allow the determination of k 1 as 1.3–0.5 +0.9 × 10–14 exp−(663 ± 144)/T cm3 s–1, corresponding to 1.4 × 10–15 cm3 s–1 at 298 K. The rate constant at 298 K is in excellent agreement with previous work, but the observed temperature dependence is less than was previously reported. The deuterium isotope effect, k H/k D, can be expressed in the Arrhenius form as k 1/k 3 = (1.7–0.4 +0.5) exp((306 ± 70)/T). The deuterium isotope effect does not appear to be greatly influenced by tunneling, which is consistent with a previous theoretical work by Hu and Dibble. (Hu, H.; Dibble, T. S., J. Phys. Chem. A 2013, 117, 14230–14242.)
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