Journals with open-discussion forums are excellent educational resources for peer review training exercises

Journals with open-discussion forums lend themselves well for peer review exercises to train early career scientists. Earth System Science Data (ESSD) is an open-access journal for the publication of interdisciplinary datasets and articles, and it is thus an example of an educational resource in the peer review process. We offer our experiences in peer review training with manuscripts submitted to ESSD, and we do so from the disparate perspectives of workshop instructor, student, and author. We then provide recommendations for the structure of a peer review workshop. We seek to promote the use of open-discussion forums, including ESSD, for educational purposes, as they can provide mutual benefits to trainees, authors, reviewers, and editors.</p

Petrologic and geochronologic evolution of the Grenville orogen, northern Blue Ridge Province, Virginia.

Basement rocks in the northern Virginia Blue Ridge include petrologically diverse granitoids and granitic gneisses that collectively record over 100 m.y. of Grenville orogenic history. New U-Pb sensitive high-resolution ion microprobe (SHRIMP) isotopic analyses of zircon indicate igneous crystallization ages of 1159 ± 14 Ma (high-silica charnockite), 1078 ± 9 Ma (leucogranite gneiss), 1060 ± 5 Ma (Old Rag magmatic series), and 1050 ± 8 Ma (low-silica charnockite). These ages, together with SHRIMP and thermal ionization mass spectrometry (TIMS) ages from previous studies, define three intervals of Grenville-age magmatic activity: Ca. 1160-1140 Ma (Magmatic Interval I), ca. 1112 Ma (Magmatic Interval II), and ca. 1080-1050 Ma (Magmatic Interval III). Field relations and ages of crosscutting igneous units indicate that a high-grade deformation event, likely associated with Ottawan orogenesis, occurred between 1078 and 1050 Ma. All rocks display tholeiitic affinity and trace-element concentrations indicative of derivation from heterogenous sources. The low-silica charnockite exhibits A-type geochemical affinity; however, all other meta-igneous rocks are compositionally transitional between A-types and fractionated I-types. Similar ages of magmatism in the Blue Ridge and Adirondacks indicate that meta-igneous rocks in both massifs define age clusters that both predate and postdate the main pulse of local Ottawan orogenesis. Late- to postorogenic A-type magmatism is represented by the 1050 Ma low-silica charnockite in the Blue Ridge and the 1060-1045 Ma Lyon Mountain granitic gneiss in the Adirondacks. Zircons from Blue Ridge granitoids emplaced during Magmatic Interval III preserve evidence of thermal effects associated with waning stages of Ottawan orogenesis at ca. 1020 Ma and 980 Ma

Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere

A growing number of ambient measurements of isocyanic acid (HNCO) are being made, yet little is known about its fate in the atmosphere. To better understand HNCO's loss processes and particularly its atmospheric partitioning behaviour, we measure its effective Henry's Law coefficient <i>K</i>_H^eff with a bubbler experiment using chemical ionization mass spectrometry as the gas phase analytical technique. By conducting experiments at different pH values and temperature, a Henry's Law coefficient <i>K</i>_H of 26 ± 2 M atm^&minus;1 is obtained, with an enthalpy of dissolution of &minus;34 ± 2 kJ mol^&minus;1, which translates to a <i>K</i>_H^eff of 31 M atm^&minus;1 at 298 K and at pH 3. Our approach also allows for the determination of HNCO's acid dissociation constant, which we determine to be <i>K</i>_a = 2.1 ± 0.2  ×  10^&minus;4 M at 298 K. Furthermore, by using ion chromatography to analyze aqueous solution composition, we revisit the hydrolysis kinetics of HNCO at different pH and temperature conditions. Three pH-dependent hydrolysis mechanisms are in play and we determine the Arrhenius expressions for each rate to be <i>k</i>₁ = (4.4 ± 0.2)  ×  10⁷ exp(&minus;6000 ± 240∕<i>T</i>) M s^&minus;1, <i>k</i>₂ = (8.9 ± 0.9)  ×  10⁶  exp(&minus;6770 ± 450∕<i>T</i>) s⁻¹ and <i>k</i>₃ =  (7.2 ± 1.5)  ×  10⁸ exp(&minus;10 900 ± 1400∕<i>T</i>) s^&minus;1, where <i>k</i>₁ is for HNCO + H⁺+ H₂O  →  NH₄⁺+ CO₂, <i>k</i>₂ is for HNCO + H₂O  →  NH₃ + CO₂ and <i>k</i>₃ is for NCO^&minus;+ 2 H₂O  →  NH₃+ HCO₃^&minus;. HNCO's lifetime against hydrolysis is therefore estimated to be 10 days to 28 years at pH values, liquid water contents, and temperatures relevant to tropospheric clouds, years in oceans and months in human blood. In all, a better parameterized Henry's Law coefficient and hydrolysis rates of HNCO allow for more accurate predictions of its concentration in the atmosphere and consequently help define exposure of this toxic molecule

Seasonal variations in the production of singlet oxygen and organic triplet excited states in aqueous PM_2.5 in Hong Kong SAR, South China

Photooxidants drive many atmospheric chemical processes. The photoexcitation of light-absorbing organic compounds (i.e., brown carbon, BrC) in atmospheric waters can lead to the generation of reactive organic triplet excited states (3C∗), which can undergo further reactions to produce other photooxidants such as singlet oxygen (1O2∗). To determine the importance of these aqueous photooxidants in secondary organic aerosol (SOA) formation and transformation, we must know their steady-state concentrations and quantum yields. However, there have been limited measurements of aqueous 3C∗ and 1O2∗ in atmospheric samples outside of North America and Europe. In this work, we report the first measurements of the steady-state concentrations and quantum yields of 3C∗ and 1O2∗ produced in aerosols in South China. We quantified the production of 3C∗ and 1O2∗ in illuminated aqueous extracts of PM2.5 collected in different seasons at two urban sites and one coastal semi-rural site during a year-round study conducted in Hong Kong SAR, South China. The mass absorption coefficients at 300 nm for BrC in the aqueous PM2.5 extracts ranged from 0.49 to 2.01 m2 g-C−1 for the three sites. Both 1O2∗ and 3C∗ were produced year-round. The steady-state concentrations of 1O2∗ ([1O2∗]ss) in the illuminated aqueous extracts ranged from 1.56×10-14 to 1.35×10-12 M, with a study average of (4.02±3.52)×10-13 M. At nearly 2 orders of magnitude lower than [1O2∗]ss, the steady-state concentrations of 3C∗ ([3C∗]ss) ranged from 2.93×10-16 to 8.08×10-14 M, with a study average of (1.09±1.39)×10-14 M. The quantum yields of 1O2∗ and 3C∗ also spanned wide ranges across samples, with a range of 1.19 % to 13.74 % and an average of (5.19±2.63) % for 1O2∗ and a range of 0.05 % to 3.24 % and an average of (0.56±0.66) % for 3C∗. The [1O2∗]ss and [3C∗]ss correlated with the concentration and absorbance of BrC, thus implying that the amount of BrC drives the steady-state concentrations of these photooxidants. The locations (urban vs. semi-rural) did not have a significant effect on [3C∗]ss and [1O2∗]ss, which indicated that BrC from local sources did not have a significant influence on the year-round 3C∗ and 1O2∗ production. 3C∗ and 1O2∗ production were found to be the highest in winter and the lowest in summer for all three sites. The observed seasonal trends of 1O2∗ and 3C∗ production could be attributed to the seasonal variations in the long-range air mass transport. Our analysis highlighted the key role that regional sources play in influencing the composition and concentrations of water-soluble BrC in winter PM2.5 in Hong Kong SAR, which contributed to their highest 3C∗ and 1O2∗ production. The current results will be useful for modeling seasonal aqueous organic aerosol photochemistry in the South China region.</p

Grenvillian magmatism in the northern Virginia Blue Ridge: Petrologic implications of episodic granitic magma production and the significance of postorogenic A-type charnockite

Grenvillian (1.2 to 1.0 Ga) plutonic rocks in northern Virginia preserve evidence of episodic, mostly granitic magmatism that spanned more than 150 million years (m.y.) of crustal reworking. Crystallization ages determined by sensitive high resolution ion microprobe (SHRIMP) U-Pb isotopic analyses of zircon and monazite, combined with results from previous studies, define three periods of magmatic activity at 1183-1144 Ma (Magmatic Interval I), 1120-1111 Ma (Magmatic Interval II), and 1078-1028 Ma (Magmatic Interval III). Magmatic activity produced dominantly tholeiitic plutons composed of (1) low-silica charnockite, (2) leucogranite, (3) non-leucocratic granitoid (with or without orthopyroxene (opx)), and (4) intermediate biotite-rich granitoid. Field, petrologic, geochemical, and geochronologic data indicate that charnockite and non-charnockitic granitoids were closely associated in both space and time, indicating that presence of opx is related to magmatic conditions, not metamorphic grade. Geochemical and Nd isotopic data, combined with results from experimental studies, indicate that leucogranites (Magmatic Intervals I and III) and non-leucocratic granitoids (Magmatic Intervals I and II) were derived from parental magmas produced by either a high degree of partial melting of isotopically evolved tonalitic sources or less advanced partial melting of dominantly tonalitic sources that also included a more mafic component. Post-orogenic, circa 1050 Ma low-silica charnockite is characterized by A-type compositional affinity including high FeOt/(FeOt + MgO), Ga/Al, Zr, Nb, Y, and Zn, and was derived from parental magmas produced by partial melting of potassic mafic sources in the lower crust. Linear geochemical trends defined by leucogranites, low-silica charnockite, and biotite-rich monzogranite emplaced during Magmatic Interval III reflect differences in source-related characteristics; these features do not represent an igneous fractionation sequence. A compositional gap between circa 1160 Ma magnesian low-silica charnockite and penecontemporaneous higher silica lithologies likewise precludes a fractionation relationship among plutons intruded during Magmatic Interval I. Correspondence in timing of magmatic activity between the Blue Ridge and neighboring Mesoproterozoic terranes underscores the widespread nature of Grenvillian processes in the region