scholarly journals Heterogeneity and chemical reactivity of the remote troposphere defined by aircraft measurements

2021 ◽  
Vol 21 (18) ◽  
pp. 13729-13746
Author(s):  
Hao Guo ◽  
Clare M. Flynn ◽  
Michael J. Prather ◽  
Sarah A. Strode ◽  
Stephen D. Steenrod ◽  
...  
Keyword(s):  
Chemical Reactivity ◽  
Chemical Species ◽  
Tropospheric Chemistry ◽  
Organic Nitrates ◽  
Data Set ◽  
Tropical Oceans ◽  
The Pacific ◽  
Probability Densities ◽  
Remote Troposphere ◽  
Modeling Data

Abstract. The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. In this paper we present and analyze a data set of 10 s (2 km) merged and gap-filled observations of the key reactive species driving the chemical budgets of O3 and CH4 (O3, CH4, CO, H2O, HCHO, H2O2, CH3OOH, C2H6, higher alkanes, alkenes, aromatics, NOx, HNO3, HNO4, peroxyacetyl nitrate, other organic nitrates), consisting of 146 494 distinct air parcels from ATom deployments 1 through 4. Six models calculated the O3 and CH4 photochemical tendencies from this modeling data stream for ATom 1. We find that 80 %–90 % of the total reactivity lies in the top 50 % of the parcels and 25 %–35 % in the top 10 %, supporting previous model-only studies that tropospheric chemistry is driven by a fraction of all the air. In other words, accurate simulation of the least reactive 50 % of the troposphere is unimportant for global budgets. Surprisingly, the probability densities of species and reactivities averaged on a model scale (100 km) differ only slightly from the 2 km ATom data, indicating that much of the heterogeneity in tropospheric chemistry can be captured with current global chemistry models. Comparing the ATom reactivities over the tropical oceans with climatological statistics from six global chemistry models, we find excellent agreement with the loss of O3 and CH4 but sharp disagreement with production of O3. The models sharply underestimate O3 production below 4 km in both Pacific and Atlantic basins, and this can be traced to lower NOx levels than observed. Attaching photochemical reactivities to measurements of chemical species allows for a richer, yet more constrained-to-what-matters, set of metrics for model evaluation.

scholarly journals Heterogeneity and Chemical Reactivity of the Remote Troposphere defined by Aircraft Measurements

2021 ◽  
Author(s):  
Hao Guo ◽  
Clare M. Flynn ◽  
Michael J. Prather ◽  
Sarah A. Strode ◽  
Stephen D. Steenrod ◽  
...  
Keyword(s):  
Data Stream ◽  
Chemical Reactivity ◽  
Probability Distributions ◽  
Organic Nitrates ◽  
Gaseous Species ◽  
Core Species ◽  
The Pacific ◽  
Remote Troposphere ◽  
Modeling Data

Abstract. The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic Oceans. ATom measured numerous gases and aerosols, particularly the gaseous species driving the chemical budgets of O3 and CH4: i.e., O3, CH4, CO, C2H6, higher alkanes, alkenes, aromatics, NOx, HNO3, HNO4, peroxyacetylnitrate, other organic nitrates, H2O, HCHO, H2O2, and CH3OOH. From the 10 s (2 km) merged observations, a modeling data stream (MDS) based on observations of the core species, consisting of 146,494 distinct air parcels has been constructed from the 4 ATom deployments, providing a continuous data stream for initializing global chemistry models and calculating the 24-hour chemical tendencies. Tendencies derived from 6 chemistry models using the ATom-1 MDS tend to agree and show a highly heterogeneous troposphere where globally 10% of the parcels control as much as 40% of the budget of O3 and CH4. Surprisingly, modeled probability distributions (100-km cells) match ATom statistics (2 km parcels), indicating that the majority of the observed heterogeneity can be resolved with current global chemistry models. On the other hand, the models' own chemical climatologies underestimate O3 production below 4 km in both Pacific and Atlantic basins because they have lower NOX levels than observed.

Interactions and implications of halogens and VOCs on tropospheric oxidant cycles in the remote atmosphere

2020 ◽  
Author(s):  
Eric C. Apel
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Model Development ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Chemical Production ◽  
Four Seasons ◽  
The Pacific ◽  
Volatile Organic ◽  
Remote Troposphere

<p>Reactive halogens have wide-ranging consequences on tropospheric chemistry including ozone destruction, HOx and NOx partitioning, oxidization of volatile organic compounds (VOCs) and initiation of new particle formation. Of particular note and importance, the tropospheric Ox loss due to halogens is estimated to be between 10-20% globally, and up to 50% in some local marine environments. In this work, we include a state-of-the-art coupled halogen and VOCs chemical mechanism into the CAM-Chem global model. Complementing the model development and providing the opportunity to test the model are recent results from the NASA Atmospheric Tomography (ATom) experiment.  ATom was conducted with a heavily instrumented NASA DC-8 aircraft over the course of two and a half years, transecting the lengths of the Pacific and Atlantic Oceans during four seasons, constantly profiling from the surface (200 m) to the upper troposphere/lower stratosphere (12000 m). The ATom payload included instruments that measured both inorganic halogens and organic halogen-containing very short-lived substances (VSLS), as well as those that measured additional volatile organic compounds (VOCs), including hydrocarbons and oxygenated VOCs (OVOCs), both of which react with halogens. Modeled BrO is sensitive to the inclusion of reactions between Br and OVOCs, particularly the aldehydes, which rapidly convert Br to HBr, a far less reactive form of Br<sub>y</sub>. These reactions can have large implications in the remote troposphere where the ATom measurements have revealed significant emissions and chemical production of low molecular weight aldehydes over the remote marine environment. A version of CAM-chem, updated to include aldehyde emissions from the ocean to close the gap between models and measurements, is used in these analyses. Comparisons between measured and modeled halogen containing species, both organic and inorganic, is presented along with a summary of the implications of our findings on the overall budgets of tropospheric halogens and ozone.</p>

scholarly journals Cloud impacts on photochemistry: building a climatology of photolysis rates from the Atmospheric Tomography mission

2018 ◽  
Vol 18 (22) ◽  
pp. 16809-16828 ◽  
Author(s):  
Samuel R. Hall ◽  
Kirk Ullmann ◽  
Michael J. Prather ◽  
Clare M. Flynn ◽  
Lee T. Murray ◽  
...  
Keyword(s):  
Tropospheric Chemistry ◽  
Data Sets ◽  
Data Set ◽  
Clear Sky ◽  
Photolysis Rates ◽  
The Pacific ◽  
Chemistry Modeling ◽  
The Pacific Ocean ◽  
Cloud Modeling ◽  
The Impact

Abstract. Measurements from actinic flux spectroradiometers on board the NASA DC-8 during the Atmospheric Tomography (ATom) mission provide an extensive set of statistics on how clouds alter photolysis rates (J values) throughout the remote Pacific and Atlantic Ocean basins. J values control tropospheric ozone and methane abundances, and thus clouds have been included for more than three decades in tropospheric chemistry modeling. ATom made four profiling circumnavigations of the troposphere capturing each of the seasons during 2016–2018. This work examines J values from the Pacific Ocean flights of the first deployment, but publishes the complete Atom-1 data set (29 July to 23 August 2016). We compare the observed J values (every 3 s along flight track) with those calculated by nine global chemistry–climate/transport models (globally gridded, hourly, for a mid-August day). To compare these disparate data sets, we build a commensurate statistical picture of the impact of clouds on J values using the ratio of J-cloudy (standard, sometimes cloudy conditions) to J-clear (artificially cleared of clouds). The range of modeled cloud effects is inconsistently large but they fall into two distinct classes: (1) models with large cloud effects showing mostly enhanced J values aloft and or diminished at the surface and (2) models with small effects having nearly clear-sky J values much of the time. The ATom-1 measurements generally favor large cloud effects but are not precise or robust enough to point out the best cloud-modeling approach. The models here have resolutions of 50–200 km and thus reduce the occurrence of clear sky when averaging over grid cells. In situ measurements also average scattered sunlight over a mixed cloud field, but only out to scales of tens of kilometers. A primary uncertainty remains in the role of clouds in chemistry, in particular, how models average over cloud fields, and how such averages can simulate measurements.

scholarly journals Impact of stratospheric air and surface emissions on tropospheric nitrous oxide during ATom

2021 ◽  
Vol 21 (14) ◽  
pp. 11113-11132
Author(s):  
Yenny Gonzalez ◽  
Róisín Commane ◽  
Ethan Manninen ◽  
Bruce C. Daube ◽  
Luke D. Schiferl ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Chemical Species ◽  
N2o Emission ◽  
Data Set ◽  
Mixing Ratios ◽  
Four Seasons ◽  
The Pacific ◽  
The Rich

Abstract. We measured the global distribution of tropospheric N2O mixing ratios during the NASA airborne Atmospheric Tomography (ATom) mission. ATom measured concentrations of ∼ 300 gas species and aerosol properties in 647 vertical profiles spanning the Pacific, Atlantic, Arctic, and much of the Southern Ocean basins, nearly from pole to pole, over four seasons (2016–2018). We measured N2O concentrations at 1 Hz using a quantum cascade laser spectrometer (QCLS). We introduced a new spectral retrieval method to account for the pressure and temperature sensitivity of the instrument when deployed on aircraft. This retrieval strategy improved the precision of our ATom QCLS N2O measurements by a factor of three (based on the standard deviation of calibration measurements). Our measurements show that most of the variance of N2O mixing ratios in the troposphere is driven by the influence of N2O-depleted stratospheric air, especially at mid- and high latitudes. We observe the downward propagation of lower N2O mixing ratios (compared to surface stations) that tracks the influence of stratosphere–troposphere exchange through the tropospheric column down to the surface. The highest N2O mixing ratios occur close to the Equator, extending through the boundary layer and free troposphere. We observed influences from a complex and diverse mixture of N2O sources, with emission source types identified using the rich suite of chemical species measured on ATom and the geographical origin calculated using an atmospheric transport model. Although ATom flights were mostly over the oceans, the most prominent N2O enhancements were associated with anthropogenic emissions, including from industry (e.g., oil and gas), urban sources, and biomass burning, especially in the tropical Atlantic outflow from Africa. Enhanced N2O mixing ratios are mostly associated with pollution-related tracers arriving from the coastal area of Nigeria. Peaks of N2O are often associated with indicators of photochemical processing, suggesting possible unexpected source processes. In most cases, the results show how difficult it is to separate the mixture of different sources in the atmosphere, which may contribute to uncertainties in the N2O global budget. The extensive data set from ATom will help improve the understanding of N2O emission processes and their representation in global models.

Integrated geophysical modelling of terranes and other structural features along the western Canadian margin

1992 ◽  
Vol 29 (7) ◽  
pp. 1492-1508 ◽  
Author(s):  
S. A. Dehler ◽  
R. M. Clowes
Keyword(s):  
Seismic Refraction ◽  
Vancouver Island ◽  
Structural Features ◽  
Pacific Rim ◽  
Data Set ◽  
Reflection Seismic ◽  
Barkley Sound ◽  
The Pacific ◽  
Wrangellia Terrane ◽  
Lower Crustal

An integrated geophysical data set has been used to develop structural models across the continental margin west of Vancouver Island, Canada. A modern accretionary complex underlies the continental slope and shelf and rests against and below the allochthonous Crescent and Pacific Rim terranes. These terranes in turn abut against the pre-Tertiary Wrangellia terrane that constitutes most of the island. Gravity and magnetic anomaly data, constrained by seismic reflection, seismic refraction, and other data, were interpreted to determine the offshore positions of these terranes and related features. Iterative 2.5-dimensional forward models of anomaly profiles were stepped laterally along the margin to extend areal coverage over a 70 km wide swath oriented normal to the tectonic features. An average model was then developed to represent this part of the margin. The Pacific Rim terrane appears to be continuous and close to the coastline along the length of Vancouver Island, consistent with emplacement by strike-slip motion along the margin. The Westcoast fault, the boundary between the Pacific Rim and Wrangellia terranes, is interpreted to be 15 km farther seaward than in previous interpretations in the region of Barkley Sound. The Crescent terrane forms a thin landward-dipping slab along the southern half of the Vancouver Island margin, and cannot be confirmed along the northern part. Model results suggest the slab has buckled into an anticline beneath southern Vancouver Island and Juan de Fuca Strait, uplifting high-density lower crustal or upper mantle material close to the surface to produce the observed intense positive gravity anomaly. This geometry is consistent with emplacement of the Crescent terrane by oblique subduction.

scholarly journals Global atmospheric chemistry – which air matters

2017 ◽  
Vol 17 (14) ◽  
pp. 9081-9102 ◽  
Author(s):  
Michael J. Prather ◽  
Xin Zhu ◽  
Clare M. Flynn ◽  
Sarah A. Strode ◽  
Jose M. Rodriguez ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Climate Models ◽  
Ocean Basin ◽  
Central Pacific ◽  
Central Pacific Ocean ◽  
Methane Budget ◽  
As Species ◽  
The Pacific ◽  
Key Species ◽  
Probability Densities

Abstract. An approach for analysis and modeling of global atmospheric chemistry is developed for application to measurements that provide a tropospheric climatology of those heterogeneously distributed, reactive species that control the loss of methane and the production and loss of ozone. We identify key species (e.g., O3, NOx, HNO3, HNO4, C2H3NO5, H2O, HOOH, CH3OOH, HCHO, CO, CH4, C2H6, acetaldehyde, acetone) and presume that they can be measured simultaneously in air parcels on the scale of a few km horizontally and a few tenths of a km vertically. As a first step, six global models have prepared such climatologies sampled at the modeled resolution for August with emphasis on the vast central Pacific Ocean basin. Objectives of this paper are to identify and characterize differences in model-generated reactivities as well as species covariances that could readily be discriminated with an unbiased climatology. A primary tool is comparison of multidimensional probability densities of key species weighted by the mass of such parcels or frequency of occurrence as well as by the reactivity of the parcels with respect to methane and ozone. The reactivity-weighted probabilities tell us which parcels matter in this case, and this method shows skill in differentiating among the models' chemistry. Testing 100 km scale models with 2 km measurements using these tools also addresses a core question about model resolution and whether fine-scale atmospheric structures matter to the overall ozone and methane budget. A new method enabling these six global chemistry–climate models to ingest an externally sourced climatology and then compute air parcel reactivity is demonstrated. Such an objective climatology containing these key species is anticipated from the NASA Atmospheric Tomography (ATom) aircraft mission (2015–2020), executing profiles over the Pacific and Atlantic Ocean basins. This modeling study addresses a core part of the design of ATom.

scholarly journals The political biogeography of migratory marine predators

2019 ◽  
Author(s):  
Autumn-Lynn Harrison
Keyword(s):  
Pacific Ocean ◽  
The Political ◽  
Migratory Species ◽  
Data Set ◽  
Leatherback Turtles ◽  
Annual Cycles ◽  
Marine Predators ◽  
The Pacific ◽  
The Pacific Ocean ◽  
International Strategies

We synthesized a large tracking data set from the Tagging of Pacific Predators to show how the movements and migratory phenology of 1,648 individuals representing 14 species—from leatherback turtles to white sharks—relate to the geopolitical boundaries of the Pacific Ocean throughout species’ annual cycles. Cumulatively, these species visited 86% of Pacific Ocean countries and some spent three-quarters of their annual cycles in the high seas. With our results, we offer answers to questions posed when designing international strategies for managing migratory species.

scholarly journals Ozone and carbon monoxide observations over open oceans on R/V <i>Mirai</i> from 67° S to 75° N during 2012 to 2017: Testing global chemical reanalysis in terms of Arctic processes, low ozone levels at low latitudes, and pollution transport

2019 ◽  
Author(s):  
Yugo Kanaya ◽  
Kazuyuki Miyazaki ◽  
Fumikazu Taketani ◽  
Takuma Miyakawa ◽  
Hisahiro Takashima ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Atmospheric Chemistry ◽  
Critical Evaluation ◽  
Chemical Transport ◽  
Tropospheric Chemistry ◽  
Set Covering ◽  
The Arctic ◽  
Pollution Transport ◽  
Data Set ◽  
Air Masses

Abstract. Constraints from ozone (O3) observations over oceans are needed in addition to those from terrestrial regions to fully understand global tropospheric chemistry and its impact on the climate. Here, we provide a large data set of ozone and carbon monoxide (CO) levels observed (for 11 666 and 10 681 h, respectively) over oceans. The data set is derived from observations made during 24 research cruise legs of R/V Mirai during 2012 to 2017, in the Southern, Indian, Pacific, and Arctic Oceans, covering the region from 67° S to 75° N. The data are suitable for critical evaluation of the over-ocean distribution of ozone derived from chemical transport models. We first give an overview of the statistics in the data set and highlight key features in terms of geographical distribution and air mass type. We then use the data set to evaluate ozone concentration fields from Tropospheric Chemistry Reanalysis version 2 (TCR-2), produced by assimilating a suite of satellite observations of multiple species into a chemical transport model, namely CHASER. For long-range transport of polluted air masses from continents to the oceans, during which the effects of forest fires and fossil fuel combustion were recognized, TCR-2 gave an excellent performance in reproducing the observed temporal variations and photochemical buildup of O3 when assessed from ΔO3 / ΔCO ratios. For clean marine conditions with low and stable CO concentrations, two focused analyses were performed. The first was in the Arctic (> 70° N) in September every year from 2013 to 2016; TCR-2 underpredicted O3 levels by 6.7 ppb (21 %) on average. The observed vertical profiles from O3 soundings from R/V Mirai during September 2014 had less steep vertical gradients at low altitudes (> 850 hPa) than those obtained TCR-2. This suggests the possibilities of more efficient descent of the O3-rich air from above or less efficient dry deposition on the surface than were assumed in the model. In the second analysis, over the western Pacific equatorial region (125–165° E, 10° S to 25° N), the observed O3 level frequently decreased to less than 10 ppb in comparison to that obtained with TCR-2, and also those obtained in most of the Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP) model runs for the decade from 2000. These results imply loss processes that are unaccounted for in the models. We found that the model’s positive bias positively correlated with the daytime residence times of air masses over a particular grid, namely 165–180° E and 15–30° N; an additional loss rate of 0.25 ppb h−1 in the grid best explained the gap. Halogen chemistry, which is commonly omitted from currently used models, might be active in this region and could have contributed to additional losses. Our open data set covering wide ocean regions is complementary to the Tropospheric Ozone Assessment Report data set, which basically comprises ground-based observations, and enables a fully global study of the behavior of O3.

TOPOLOGICAL INDICES – WHY AND HOW

2021 ◽  
Author(s):  
Ivan Gutman ◽  
Keyword(s):  
Single Molecule ◽  
Chemical Structure ◽  
Chemical Reactivity ◽  
Chemical Species ◽  
Chemical Compounds ◽  
Simple Calculation ◽  
Topological Indices ◽  
High Level ◽  
Complex Phenomena ◽  
Real World Problems

By means of presently available high-level computational methods, based on quantum theory, it is possible to determine (predict) the main structural, electronic, energetic, geometric, and thermodynamic properties of a particular chemical species (usually a molecule), as well as the ways in which it changes in chemical reactions. When one needs to estimate such properties of thousands or millions of chemical species, such high-level calculations are no more feasible. Then simpler, but less accurate, approaches are necessary. One such approach utilized so-called “topological indices”. According to IUPAC ‘s definition [Pure Appl. Chem. 69 (1997) 1137]: A topological index is a numerical value associated with chemical constitution for correlation of chemical structure with various physical properties, chemical reactivity or biological activity. In the first part of the lecture, we show that „numerical values“are associated with many other complex phenomena, encountered in various areas of human activity, implying that „topological indices“ are used far beyond chemistry. Next, we discuss the number of possible chemical compounds. Simple calculation shows that the number of possible compounds zillion times exceeds the number of those that have been experimentally characterized. Even worse, in the entire Universe, there is not enough matter to make at least a single molecule of each possible compound. In the second part of the lecture, a few most popular topological indices will be presented, as well as the way in which these can be (and are being) applied in treating real-world problems.

scholarly journals Decadal Timescale Shift in the 14C Record of a Central Equatorial Pacific Coral

Radiocarbon ◽  
2003 ◽  
Vol 45 (1) ◽  
pp. 91-99 ◽  
Author(s):  
A G Grottoli ◽  
S T Gille ◽  
E R M Druffel ◽  
R B Dunbar
Keyword(s):  
Mass Movement ◽  
Relative Increase ◽  
Equatorial Pacific ◽  
Windward Side ◽  
Common Mechanism ◽  
Positive Shift ◽  
Tropical Oceans ◽  
The Pacific ◽  
Central Equatorial Pacific ◽  
History Of

Coral skeletal radiocarbon records reflect seawater ∆14C and are useful for reconstructing the history of water mass movement and ventilation in the tropical oceans. Here, we reconstructed the inter-annual variability in central equatorial Pacific surface water ∆14C from 1922–1956 using near-monthly 14C measurements in a Porites sp. coral skeleton (FI5A) from the windward side of Fanning Island (3°54′32′′N, 159°18'88′′W). The most pronounced feature in this record is a large, positive shift in the ∆14C between 1947 and 1956 that coincides with the switch of the Pacific Decadal Oscillation (PDO) from a positive to a negative phase in the mid-1940s. Although the absolute ∆14C values from 1950–1955 in FI5A differ from the ∆14C values of another coral core collected from the opposite side of the island, both records show a large, positive shift in their ∆14C records at that time. The relative increase in the ∆14C of each record is consistent with the premise that a common mechanism is controlling the ∆14C records within each coral record. Overall, the Fanning ∆14C data support the notion that a significant amount of subtropical seawater is arriving at the Equator, but does not allow us to determine the mechanism for its transport.

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