scholarly journals Active and widespread halogen chemistry in the tropical and subtropical free troposphere

2015 ◽  
Vol 112 (30) ◽  
pp. 9281-9286 ◽  
Author(s):  
Siyuan Wang ◽  
Johan A. Schmidt ◽  
Sunil Baidar ◽  
Sean Coburn ◽  
Barbara Dix ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Oxidative Capacity ◽  
Free Troposphere ◽  
Mercury Deposition ◽  
Tropical Eastern Pacific ◽  
Ice Clouds ◽  
Bromine Oxide ◽  
Halogen Chemistry ◽  
Model Predictions ◽  
Wet Scavenging

Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O3 and methane (CH4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O3. The observed BrO concentrations increase strongly with altitude (∼3.4 pptv at 13.5 km), and are 2–4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5–6.4 pptv total inorganic bromine (Bry), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. The halogen-catalyzed loss of tropospheric O3 needs to be considered when estimating past and future ozone radiative effects.

scholarly journals Rapid formation of isoprene photo-oxidation products observed in Amazonia

2009 ◽  
Vol 9 (3) ◽  
pp. 13629-13653 ◽  
Author(s):  
T. Karl ◽  
A. Guenther ◽  
A. Turnipseed ◽  
P. Artaxo ◽  
S. Martin
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Oxidative Capacity ◽  
Oxidation Products ◽  
Lower Atmosphere ◽  
Peroxy Radicals ◽  
Aerosol Formation ◽  
Photo Oxidation ◽  
Voc Oxidation ◽  
Rapid Formation

Abstract. Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photo-oxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian aerosol characterization experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photo-oxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. A recently suggested novel pathway for isoprene peroxy radicals could explain the observed discrepancy and reconcile the rapid formation of these VOCs. Furthermore, if generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in substantial underestimates of modelled OH reactivity that could explain a major fraction of the missing OH sink over forests which has previously been attributed to a missing source of primary biogenic VOCs.

Surface-Promoted Redox Reactions Occurs Spontaneously on Solvating Salt Surfaces

2021 ◽  
Author(s):  
Xiangrui Kong ◽  
Ivan Gladich ◽  
Dimitri Castarede ◽  
Erik Thomson ◽  
Anthony Boucly ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Photoelectron Spectroscopy ◽  
Ambient Pressure ◽  
Species Abundance ◽  
Ammonium Oxidation ◽  
Gas Uptake ◽  
Sulfate Reducing ◽  
Interfacial Processes ◽  
Key Species ◽  
Halogen Chemistry

<p>Gas-particle interfaces play essential roles in the atmosphere and directly influence many atmospheric processes, including gas uptake, halogen chemistry, ozone depletion, and heterogeneous ice nucleation. However, because interfacial processes take place on molecular scales, classical bulk thermodynamic theories are often insufficient to describe interfaces. Also, interfacial processes are challenging to characterize and are often overlooked in current atmospheric chemistry.</p><p>For this study, ambient pressure X-ray photoelectron spectroscopy (APXPS) experiments were performed. A surface-promoted sulfate-reducing ammonium oxidation reaction is discovered to spontaneously take place on common inorganic aerosol surfaces undergoing solvation. Several key intermediate species including, S<sup>0</sup>, HS<sup>-</sup>, HONO, and NH<sub>3(aq)</sub> are identified as reaction components associated with the solvation process. Depth profiles of relative species abundance show the surface propensity of key species. The species assignments and depth profile features are supported by classical and first-principle molecular dynamics calculations. A detailed mechanism is proposed to describe the processes that lead to unexpected products during salt solvation. This discovery reveals novel chemistry that is uniquely linked to a solvating surface and has great potential to illuminate current puzzles within heterogeneous chemistry. Lastly, natural salts sampled from saline lakes and playas are examined for this behavior, and provide further evidence of the important roles this surface-promoted redox mechanism may play in nature.</p>

scholarly journals OH and HO<sub>2</sub> radical chemistry in a midlatitude forest: Measurements and model comparisons

2019 ◽  
Author(s):  
Michelle L. Lew ◽  
Pamela S. Rickly ◽  
Brandon P. Bottorff ◽  
Sofia Sklaveniti ◽  
Thierry Léonardis ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Peroxy Radicals ◽  
Mixing Ratios ◽  
Photolysis Rates ◽  
Model Predictions ◽  
Ho2 Radical

Abstract. Reactions of the hydroxyl (OH) and peroxy radicals (HO2 and RO2) play a central role in the chemistry of the atmosphere. In addition to controlling the lifetimes of many trace gases important to issues of global climate change, OH radical reactions initiate the oxidation of volatile organic compounds (VOCs) which can lead to the production of ozone and secondary organic aerosols in the atmosphere. Previous measurements of these radicals in forest environments characterized by high mixing ratios of isoprene and low mixing ratios of nitrogen oxides (NOx) have shown serious discrepancies with modeled concentrations. These results bring into question our understanding of the atmospheric chemistry of isoprene and other biogenic VOCs under low NOx conditions. During the summer of 2015, OH and HO2 radical concentrations as well as total OH reactivity were measured using Laser-Induced Fluorescence - Fluorescence Assay by Gas Expansion (LIF-FAGE) techniques as part of the Indiana Radical, Reactivity and Ozone Production Intercomparison (IRRONIC). This campaign took place in a forested area near the Indiana University, Bloomington campus characterized by high mixing ratios of isoprene and low mixing ratios of NOx. Supporting measurements of photolysis rates, VOCs, NOx, and other species were used to constrain a zero-dimensional box model based on the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM). Using an OH chemical scavenger technique, the study revealed the presence of an interference with the LIF-FAGE measurements of OH that increased with both ambient concentrations of ozone and temperature. Subtraction of the interference resulted in measured OH concentrations that were in better agreement with model predictions, although the model still underestimated the measured concentrations, likely due to an underestimation of the concentration of NO at this site. Measurements of HO2 radical concentrations during the campaign included a fraction of isoprene-based peroxy radicals (HO2* = HO2 + αRO2) and were found to agree with model predictions. On average, the measured reactivity was consistent with that calculated from measured OH sinks to within 20 %, with modeled oxidation products accounting for the missing reactivity, although significant missing reactivity (approximately 40 % of the total measured reactivity) was observed on some days.

scholarly journals On the role of tropopause folds in summertime tropospheric ozone over the eastern Mediterranean and the Middle East

2016 ◽  
Vol 16 (21) ◽  
pp. 14025-14039 ◽  
Author(s):  
Dimitris Akritidis ◽  
Andrea Pozzer ◽  
Prodromos Zanis ◽  
Evangelos Tyrlis ◽  
Bojan Škerlak ◽  
...  
Keyword(s):  
Middle East ◽  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
Eastern Mediterranean ◽  
Stratospheric Ozone ◽  
Surface Ozone ◽  
Free Troposphere ◽  
Near Surface ◽  
Grid Points ◽  
High Concentrations

Abstract. We study the contribution of tropopause folds in the summertime pool of tropospheric ozone over the eastern Mediterranean and the Middle East (EMME) with the aid of the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model. Tropopause fold events in EMAC simulations were identified with a 3-D labeling algorithm that detects folds at grid points where multiple crossings of the dynamical tropopause are computed. Subsequently the events featuring the largest horizontal and vertical extent were selected for further study. For the selection of these events we identified a significant contribution of the stratospheric ozone reservoir to the high concentrations of ozone in the middle and lower free troposphere over the EMME. A distinct increase of ozone is found over the EMME in the middle troposphere during summer as a result of the fold activity, shifting towards the southeast and decreasing altitude. We find that the interannual variability of near-surface ozone over the eastern Mediterranean (EM) during summer is related to that of both tropopause folds and ozone in the free troposphere.

Major influence of BrO on the NOx and nitrate budgets in the Arctic spring, inferred from Δ17O(NO3 - ) measurements during ozone depletion events

2007 ◽  
Vol 4 (4) ◽  
pp. 238 ◽  
Author(s):  
S. Morin ◽  
J. Savarino ◽  
S. Bekki ◽  
A. Cavender ◽  
P. B. Shepson ◽  
...  
Keyword(s):  
Nitrogen Oxides ◽  
Isotopic Composition ◽  
Atmospheric Chemistry ◽  
Ozone Depletion ◽  
Lower Atmosphere ◽  
The Arctic ◽  
Major Influence ◽  
Peroxy Radicals ◽  
Bromine Oxide ◽  
Atmospheric Nitrate

Environmental context. Ozone depletion events (ODEs) in the Arctic lower atmosphere drive profound changes in the chemistry of nitrogen oxides (NOx) because of the presence of bromine oxide (BrO). These are investigated using the isotopic composition of atmospheric nitrate (NO3–), which is a ubiquitous species formed through the oxidation of nitrogen oxides. Since BrO is speculated to play a key role in the atmospheric chemistry of marine regions and in the free troposphere, our studies contribute to the improvement of the scientific knowledge on this new topic in atmospheric chemistry. Abstract. The triple oxygen isotopic composition of atmospheric inorganic nitrate was measured in samples collected in the Arctic in springtime at Alert, Nunavut and Barrow, Alaska. The isotope anomaly of nitrate (Δ17O = δ17O–0.52δ18O) was used to probe the influence of ozone (O3), bromine oxide (BrO), and peroxy radicals (RO2) in the oxidation of NO to NO2, and to identify the dominant pathway that leads to the production of atmospheric nitrate. Isotopic measurements confirm that the hydrolysis of bromine nitrate (BrONO2) is a major source of nitrate in the context of ozone depletion events (ODEs), when brominated compounds primarily originating from sea salt catalytically destroy boundary layer ozone. They also show a case when BrO is the main oxidant of NO into NO2.

Investigating the relationship between ozone and water-ice in the martian atmosphere

2020 ◽  
Author(s):  
Megan Brown ◽  
Manish Patel ◽  
Stephen Lewis ◽  
Amel Bennaceur
Keyword(s):  
Carbon Dioxide ◽  
Water Vapour ◽  
Hydroxyl Radicals ◽  
Atmospheric Chemistry ◽  
Martian Atmosphere ◽  
Reaction Rates ◽  
Chemical Processes ◽  
Ice Clouds ◽  
Water Ice ◽  
The Relationship

&lt;p&gt;This project maps ozone and ice-water clouds detected in the martian atmosphere to assess the atmospheric chemistry between ozone, water-ice and hydroxyl radicals. Hydroxyl photochemistry may be indicated by a non-negative or fluctuating correlation between ozone and water-ice. This will contribute to understanding the stability of carbon dioxide and atmospheric chemistry of Mars.&lt;/p&gt;&lt;p&gt;Ozone (O&lt;sub&gt;3&lt;/sub&gt;) can be used for tracking general circulation of the martian atmosphere and other trace chemicals, as well as acting as a proxy for water vapour. The photochemical break down of water vapour produces hydroxyl radicals known to participate in the destruction of ozone. The relationship between water vapour and ozone is therefore negatively correlated. Atmospheric water-ice concentrations may also follow this theory. The photochemical reactions between ozone, water-ice clouds and hydroxyl radicals are poorly understood in the martian atmosphere due to the short half-life and rapid reaction rates of hydroxyl radicals. These reactions destroy ozone, as well as indirectly contributing to the water cycle and stability of carbon dioxide (measured by the CO&lt;sub&gt;2&lt;/sub&gt;&amp;#8211;CO ratio). However, the detection of ozone in the presence of water-ice clouds suggests the relationship between them is not always anti-correlated. Global climate models (GCMs) struggle to describe the chemical processes occurring within water-ice clouds. For example, the heterogeneous photochemistry described in the LMD (Laboratoire de M&amp;#233;t&amp;#233;orologie Dynamique) GCM did not significantly improve the model. This leads to the following questions:&lt;em&gt; what is the relationship between water-ice clouds and ozone, and can the chemical reactions of hydroxyl radicals occurring within water-ice clouds be determined through this relationship?&lt;/em&gt;&lt;/p&gt;&lt;p&gt;This project aims to address these questions using nadir and occultation retrievals of ozone and water-ice clouds, potentially using retrievals from the UVIS instrument aboard NOMAD (Nadir and Occultation for Mars Discovery), ExoMars Trace Gas Orbiter. Analysis will include temporal and spatial binning of data to help identify any patterns present. Correlation tests will be conducted to determine the significance of any relationship at short term and seasonal scales along a range of zonally averaged latitude photochemical model from the LMD-UK GCM will be used to further explore the chemical processes.&lt;/p&gt;&lt;p&gt;Interactions between hydroxyl radicals and the surface of water-ice clouds are poorly understood. Ozone abundance is greatest in the winter at the polar regions, which also coincides with the appearance of the polar hood clouds. The use of nadir observations will enable the comparison between total column of ozone abundance at high latitudes (&gt;60&amp;#176;S) in a range of varying water-ice cloud opacities, as well as the equatorial region (30&amp;#176;S &amp;#8211; 30&amp;#176;N) during aphelion. Water-ice clouds may remove hydroxyl radicals responsible for the destruction of ozone and thus the previously assumed anticorrelation between ozone and water-ice will not hold. The project will therefore assess the hypothesis that: &lt;em&gt;water-ice clouds may act as a sink for hydroxyl radicals.&lt;/em&gt;&lt;/p&gt;

scholarly journals Atmospheric nitrogen oxides (NO and NO<sub>2</sub>) at Dome C, East Antarctica, during the OPALE campaign

2015 ◽  
Vol 15 (14) ◽  
pp. 7859-7875 ◽  
Author(s):  
M. M. Frey ◽  
H. K. Roscoe ◽  
A. Kukui ◽  
J. Savarino ◽  
J. L. France ◽  
...  
Keyword(s):  
Nitrogen Oxides ◽  
Atmospheric Chemistry ◽  
Ambient Air ◽  
Skin Layer ◽  
East Antarctica ◽  
Atmospheric Nitrogen ◽  
Bromine Oxide ◽  
Diurnal Cycles ◽  
Mixing Ratios ◽  
Air Chemistry

Abstract. Mixing ratios of the atmospheric nitrogen oxides NO and NO2 were measured as part of the OPALE (Oxidant Production in Antarctic Lands &amp; Export) campaign at Dome C, East Antarctica (75.1° S, 123.3° E, 3233 m), during December 2011 to January 2012. Profiles of NOx mixing ratios of the lower 100 m of the atmosphere confirm that, in contrast to the South Pole, air chemistry at Dome C is strongly influenced by large diurnal cycles in solar irradiance and a sudden collapse of the atmospheric boundary layer in the early evening. Depth profiles of mixing ratios in firn air suggest that the upper snowpack at Dome C holds a significant reservoir of photolytically produced NO2 and is a sink of gas-phase ozone (O3). First-time observations of bromine oxide (BrO) at Dome C show that mixing ratios of BrO near the ground are low, certainly less than 5 pptv, with higher levels in the free troposphere. Assuming steady state, observed mixing ratios of BrO and RO2 radicals are too low to explain the large NO2 : NO ratios found in ambient air, possibly indicating the existence of an unknown process contributing to the atmospheric chemistry of reactive nitrogen above the Antarctic Plateau. During 2011–2012, NOx mixing ratios and flux were larger than in 2009–2010, consistent with also larger surface O3 mixing ratios resulting from increased net O3 production. Large NOx mixing ratios at Dome C arise from a combination of continuous sunlight, shallow mixing height and significant NOx emissions by surface snow (FNOx). During 23 December 2011–12 January 2012, median FNOx was twice that during the same period in 2009–2010 due to significantly larger atmospheric turbulence and a slightly stronger snowpack source. A tripling of FNOx in December 2011 was largely due to changes in snowpack source strength caused primarily by changes in NO3− concentrations in the snow skin layer, and only to a secondary order by decrease of total column O3 and associated increase in NO3− photolysis rates. A source of uncertainty in model estimates of FNOx is the quantum yield of NO3− photolysis in natural snow, which may change over time as the snow ages.

scholarly journals Rapid formation of isoprene photo-oxidation products observed in Amazonia

2009 ◽  
Vol 9 (20) ◽  
pp. 7753-7767 ◽  
Author(s):  
T. Karl ◽  
A. Guenther ◽  
A. Turnipseed ◽  
G. Tyndall ◽  
P. Artaxo ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Field Measurements ◽  
Oxidative Capacity ◽  
Oxidation Products ◽  
Lower Atmosphere ◽  
Peroxy Radicals ◽  
Aerosol Formation ◽  
Photo Oxidation ◽  
Voc Oxidation

Abstract. Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photo-oxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian Aerosol Characterization Experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photo-oxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. Recently reported fast secondary production could explain 50% of the observed discrepancy with the remaining part possibly produced via a novel primary production channel, which has been proposed theoretically. The observations of OVOCs are also used to test a recently proposed HOx recycling mechanism via degradation of isoprene peroxy radicals. If generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in uncertainties of modelled OH reactivity, potentially explaining a fraction of the missing OH sink over forests which has previously been largely attributed to a missing source of primary biogenic VOCs.

scholarly journals A Comparative Study of Atmospheric Chemistry with VULCAN

2021 ◽  
Vol 923 (2) ◽  
pp. 264
Author(s):  
Shang-Min Tsai ◽  
Matej Malik ◽  
Daniel Kitzmann ◽  
James R. Lyons ◽  
Alexander Fateev ◽  
...  
Keyword(s):  
Cross Sections ◽  
Atmospheric Chemistry ◽  
Vertical Mixing ◽  
Giant Planets ◽  
Temperature Dependent ◽  
Ice Clouds ◽  
Various Boundary Conditions ◽  
Set Up ◽  
Vanadium Species ◽  
Titanium Vanadium

Abstract We present an update of the open-source photochemical kinetics code VULCAN to include C–H–N–O–S networks and photochemistry. The additional new features are advection transport, condensation, various boundary conditions, and temperature-dependent UV cross sections. First, we validate our photochemical model for hot Jupiter atmospheres by performing an intercomparison of HD 189733b models between Moses et al., Venot et al., and VULCAN, to diagnose possible sources of discrepancy. Second, we set up a model of Jupiter extending from the deep troposphere to upper stratosphere to verify the kinetics for low temperature. Our model reproduces hydrocarbons consistent with observations, and the condensation scheme successfully predicts the locations of water and ammonia ice clouds. We show that vertical advection can regulate the local ammonia distribution in the deep atmosphere. Third, we validate the model for oxidizing atmospheres by simulating Earth and find agreement with observations. Last, VULCAN is applied to four representative cases of extrasolar giant planets: WASP-33b, HD 189733b, GJ 436b, and 51 Eridani b. We look into the effects of the C/O ratio and chemistry of titanium/vanadium species for WASP-33b, we revisit HD 189733b for the effects of sulfur and carbon condensation, the effects of internal heating and vertical mixing (K zz) are explored for GJ 436b, and we test updated planetary properties for 51 Eridani b with S8 condensates. We find that sulfur can couple to carbon or nitrogen and impact other species, such as hydrogen, methane, and ammonia. The observable features of the synthetic spectra and trends in the photochemical haze precursors are discussed for each case.

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