The Impact of the Aqueous Phase Chemistry of HNO4 on Gas Phase Tropospheric Chemistry

2001 ◽  
Vol 32 ◽  
pp. 269-270
Author(s):  
J.E. WILLIAMS ◽  
F.J. DENTENER ◽  
A.R. van den BERG
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Tropospheric Chemistry ◽  
Phase Chemistry ◽  
The Impact

Influence of in-cloud oxidation of organic compounds on tropospheric ozone

2021 ◽  
Author(s):  
Simon Rosanka ◽  
Rolf Sander ◽  
Bruno Franco ◽  
Catherine Wespes ◽  
Andreas Wahner ◽  
...  
Keyword(s):  
Gas Phase ◽  
Organic Compounds ◽  
Aqueous Phase ◽  
Phase Transfer ◽  
Sulfur Oxidation ◽  
Box Model ◽  
Atmospheric Models ◽  
Model Studies ◽  
Phase Chemistry ◽  
The Impact

<p>Large parts of the troposphere are affected by clouds, whose aqueous-phase chemistry differs significantly from gas-phase chemistry. Box-model studies have demonstrated that clouds influence the tropospheric oxidation capacity. However, most global atmospheric models do not represent this chemistry reasonably well and are largely limited to sulfur oxidation. Therefore, we have developed the Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC), making a detailed in-cloud oxidation model of oxygenated volatile organic compounds (OVOCs) readily available for box as well as for regional and global simulations that are affordable with modern supercomputers. JAMOC includes the phase transfer of species containing up to ten carbon atoms, and the aqueous-phase reactions of a selection of species containing up to four carbon atoms, e.g., ethanol, acetaldehyde, glyoxal. The impact of in-cloud chemistry on tropospheric composition is assessed on a regional and global scale by performing a combination of box-model studies using the Chemistry As A Boxmodel Application (CAABA) and the global atmospheric model ECHAM/MESSy (EMAC). These models are capable to represent the described processes explicitly and integrate the corresponding ODE system with a Rosenbrock solver. </p><p>Overall, the explicit in-cloud oxidation leads to a reduction of predicted OVOCs levels. By comparing EMAC's prediction of methanol abundance to spaceborne retrievals from the Infrared Atmospheric Sounding Interferometer (IASI), a reduction in EMAC's overestimation is observed in the tropics. Further, the in-cloud OVOC oxidation shifts the hydroperoxyl radicals (HO<sub>2</sub>) production from the gas- to the aqueous-phase. As a result, the in-cloud destruction (scavenging) of ozone (O<sub>3</sub>) by the superoxide anion (O<sub>2</sub><sup>-</sup>) is enhanced and accompanied by a reduction in both sources and sinks of tropospheric O<sub>3</sub> in the gas phase. By considering only the in-cloud sulfur oxidation by O<sub>3</sub>, about 13 Tg a<sup>-1</sup> of O<sub>3</sub> are scavenged, which increases to 336 Tg a<sup>-1</sup> when JAMOC is used. With the full oxidation scheme, the highest O<sub>3</sub> reduction of 12 % is predicted in the upper troposphere/lower stratosphere (UTLS). Based on the IASI O<sub>3</sub> retrievals, it is demonstrated that these changes in the free troposphere significantly reduce the modelled tropospheric O<sub>3</sub> columns, which are known to be generally overestimated by global atmospheric models. Finally, the relevance of aqueous-phase oxidation of organics for ozone in hazy polluted regions will be presented.  </p>

scholarly journals Application of random forest regression to the calculation of gas-phase chemistry within the GEOS-Chem chemistry model v10

2019 ◽  
Vol 12 (3) ◽  
pp. 1209-1225 ◽  
Author(s):  
Christoph A. Keller ◽  
Mat J. Evans
Keyword(s):  
Machine Learning ◽  
Random Forest ◽  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Random Forest Regression ◽  
Data Set ◽  
Gas Phase Chemistry ◽  
Chemical Conditions ◽  
Phase Chemistry ◽  
The Impact

Abstract. Atmospheric chemistry models are a central tool to study the impact of chemical constituents on the environment, vegetation and human health. These models are numerically intense, and previous attempts to reduce the numerical cost of chemistry solvers have not delivered transformative change. We show here the potential of a machine learning (in this case random forest regression) replacement for the gas-phase chemistry in atmospheric chemistry transport models. Our training data consist of 1 month (July 2013) of output of chemical conditions together with the model physical state, produced from the GEOS-Chem chemistry model v10. From this data set we train random forest regression models to predict the concentration of each transported species after the integrator, based on the physical and chemical conditions before the integrator. The choice of prediction type has a strong impact on the skill of the regression model. We find best results from predicting the change in concentration for long-lived species and the absolute concentration for short-lived species. We also find improvements from a simple implementation of chemical families (NOx = NO + NO2). We then implement the trained random forest predictors back into GEOS-Chem to replace the numerical integrator. The machine-learning-driven GEOS-Chem model compares well to the standard simulation. For ozone (O3), errors from using the random forests (compared to the reference simulation) grow slowly and after 5 days the normalized mean bias (NMB), root mean square error (RMSE) and R2 are 4.2 %, 35 % and 0.9, respectively; after 30 days the errors increase to 13 %, 67 % and 0.75, respectively. The biases become largest in remote areas such as the tropical Pacific where errors in the chemistry can accumulate with little balancing influence from emissions or deposition. Over polluted regions the model error is less than 10 % and has significant fidelity in following the time series of the full model. Modelled NOx shows similar features, with the most significant errors occurring in remote locations far from recent emissions. For other species such as inorganic bromine species and short-lived nitrogen species, errors become large, with NMB, RMSE and R2 reaching >2100 % >400 % and <0.1, respectively. This proof-of-concept implementation takes 1.8 times more time than the direct integration of the differential equations, but optimization and software engineering should allow substantial increases in speed. We discuss potential improvements in the implementation, some of its advantages from both a software and hardware perspective, its limitations, and its applicability to operational air quality activities.

scholarly journals Do organic surface films on sea salt aerosols influence atmospheric chemistry? – a model study

2007 ◽  
Vol 7 (21) ◽  
pp. 5555-5567 ◽  
Author(s):  
L. Smoydzin ◽  
R. von Glasow
Keyword(s):  
Mass Transfer ◽  
Liquid Phase ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Atmospheric Chemistry ◽  
Organic Coating ◽  
Sea Salt ◽  
Tropospheric Chemistry ◽  
Special Focus ◽  
Sea Salt Aerosols

Abstract. Organic material from the ocean's surface can be incorporated into sea salt aerosol particles often producing a surface film on the aerosol. Such an organic coating can reduce the mass transfer between the gas phase and the aerosol phase influencing sea salt chemistry in the marine atmosphere. To investigate these effects and their importance for the marine boundary layer (MBL) we used the one-dimensional numerical model MISTRA. We considered the uncertainties regarding the magnitude of uptake reduction, the concentrations of organic compounds in sea salt aerosols and the oxidation rate of the organics to analyse the possible influence of organic surfactants on gas and liquid phase chemistry with a special focus on halogen chemistry. By assuming destruction rates for the organic coating based on laboratory measurements we get a rapid destruction of the organic monolayer within the first meters of the MBL. Larger organic initial concentrations lead to a longer lifetime of the coating but lead also to an unrealistically strong decrease of O3 concentrations as the organic film is destroyed by reaction with O3. The lifetime of the film is increased by assuming smaller reactive uptake coefficients for O3 or by assuming that a part of the organic surfactants react with OH. With regard to tropospheric chemistry we found that gas phase concentrations for chlorine and bromine species decreased due to the decreased mass transfer between gas phase and aerosol phase. Aqueous phase chlorine concentrations also decreased but aqueous phase bromine concentrations increased. Differences for gas phase concentrations are in general smaller than for liquid phase concentrations. The effect on gas phase NO2 or NO is very small (reduction less than 5%) whereas liquid phase NO2 concentrations increased in some cases by nearly 100%. We list suggestions for further laboratory studies which are needed for improved model studies.

Modelling the photochemical formation of high H2O2 concentrations and secondary sulfate observed during winter haze periods in the NCP

2020 ◽  
Author(s):  
Andreas Tilgner ◽  
Erik Hans Hoffmann ◽  
Lin He ◽  
Bernd Heinold ◽  
Can Ye ◽  
...  
Keyword(s):  
Air Pollution ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Photochemical Reactions ◽  
Data Availability ◽  
Phase Reaction ◽  
Aerosol Composition ◽  
Chemistry Research ◽  
The Impact

&lt;p&gt;During winter, the North China Plain (NCP) is frequently characterized by severe haze conditions connected with extremely high PM2.5 and NOx concentrations, i.e. strong air pollution. The NCP is one of the most populated regions worldwide where haze periods have direct health effects. Tropospheric haze particles are a complex multiphase and multi-component environment, in which multiphase chemical processes are able to alter the chemical aerosol composition and deduced physical aerosol properties and can strongly contribute to air pollution. Despite many past investigations, the chemical haze processing is still uncertain and represents a challenge to atmospheric chemistry research. Recent NCP studies during autumn/winter 2017 haze periods have revealed unexpected high H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentrations of about 1&amp;#160;ppb suggesting H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; as a potential contributor to secondary PM2.5 mass, e.g., due to sulfur(IV) oxidation. However, the multiphase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation under such NOx concentrations is still unclear. Therefore, the present study aimed at the examination of potential multiphase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation pathways, and the feedback on sulfur oxidation.&lt;/p&gt;&lt;p&gt;Multiphase chemistry simulations of a measurement campaign in the NCP are performed with the box model SPACCIM. The multiphase chemistry model within SPACCIM contains the gas-phase mechanism MCMv3.2 and the aqueous-phase mechanism CAPRAM4.0 together with both its aromatics module CAPRAM-AM1.0 and its halogen module CAPRAM-HM2.1. Furthermore, based on available literature data, the multiphase chemistry mechanism is extended considering further multiphase formation pathways of HONO and an advanced HOx mechanism scheme enabling higher in-situ H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formations in haze particles. The simulations have been performed for three periods characterized by high H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentrations, high RH and PM2.5 conditions and high measurement data availability. Several sensitivity runs have been performed examining the impact of the soluble transition metal ion (TMI) content on the predicted H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation.&lt;/p&gt;&lt;p&gt;Simulations with the improved multiphase chemistry mechanism shows a good agreement of the modelled H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentrations with field data. The modelled H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentration shows a substantial dependency on the soluble TMI content. Higher soluble TMI contents result in higher H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentrations demonstrating the strong influence of TMI chemistry in haze particles on H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation. The analysis of the chemical production and sink fluxes reveals that a huge fraction of the multiphase HO&lt;sub&gt;2&lt;/sub&gt; radicals and nearly all of the subsequently formed reaction product H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; is produced in-situ within the haze particles and does not origin from the gas phase. Further chemical analyses show that, during the morning hours, the aqueous-phase reaction of H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; with S(IV) contributes considerably to S(VI) formation beside the HONO related formation of sulfuric acid by OH in the gas-phase.&lt;/p&gt;&lt;p&gt;Finally, a parameterization was developed to study the particle-phase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formations as potential source with the global model ECHAM-HAMMOZ. The performed global modelling identifies an increase of gas-phase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; by a factor of 2.8 through the newly identified particle chemistry. Overall, the study demonstrated that photochemical reactions of HULIS and TMIs in particles are an important H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; source leading to increased particle sulfate formation.&lt;/p&gt;

scholarly journals Tropospheric Aqueous-Phase Chemistry: Kinetics, Mechanisms, and Its Coupling to a Changing Gas Phase

2015 ◽  
Vol 115 (10) ◽  
pp. 4259-4334 ◽  
Author(s):  
Hartmut Herrmann ◽  
Thomas Schaefer ◽  
Andreas Tilgner ◽  
Sarah A. Styler ◽  
Christian Weller ◽  
...  
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Phase Chemistry

Impacts of monocyclic aromatics on regional and global tropospheric gas-phase chemistry

2020 ◽  
Author(s):  
Rolf Sander ◽  
David Cabrera-Perez ◽  
Sara Bacer ◽  
Sergey Gromov ◽  
Jos Lelieveld ◽  
...  
Keyword(s):  
East Asia ◽  
Gas Phase ◽  
Aromatic Compounds ◽  
General Circulation ◽  
Regional Scale ◽  
Circulation Model ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

&lt;p&gt;Aromatic compounds in the troposphere are reactive towards ozone&lt;br&gt;(O&lt;sub&gt;3&lt;/sub&gt;), hydroxyl (OH) and other radicals. Here we present an&lt;br&gt;assessment of their impacts on the gas-phase chemistry, using the&lt;br&gt;general circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry). The&lt;br&gt;monocyclic aromatics considered in this study comprise benzene, toluene,&lt;br&gt;xylenes, phenol, styrene, ethylbenzene, trimethylbenzenes, benzaldehyde&lt;br&gt;and lumped higher aromatics bearing more than 9 C atoms. On a global&lt;br&gt;scale, the estimated net changes are minor when aromatic compounds are&lt;br&gt;included in the chemical mechanism of our model. For instance, the&lt;br&gt;tropospheric burden of CO increases by about 6 %, and those of OH,&lt;br&gt;O&lt;sub&gt;3&lt;/sub&gt;, and NO&lt;sub&gt;x&lt;/sub&gt; (NO + NO&lt;sub&gt;2&lt;/sub&gt;) decrease between&lt;br&gt;2 % and 14 %. The global mean changes are small partially because of&lt;br&gt;compensating effects between high- and low-NO&lt;sub&gt;x&lt;/sub&gt; regions. The&lt;br&gt;largest change is predicted for glyoxal, which increases globally by 36&lt;br&gt;%. Significant regional changes are identified for several species. For&lt;br&gt;instance, glyoxal increases by 130 % in Europe and 260 % in East Asia,&lt;br&gt;respectively. Large increases in HCHO are also predicted in these&lt;br&gt;regions. In general, the influence of aromatics is particularly evident&lt;br&gt;in areas with high concentrations of NO&lt;sub&gt;x&lt;/sub&gt;, with increases up&lt;br&gt;to 12 % in O&lt;sub&gt;3&lt;/sub&gt; and 17 % in OH. Although the global impact of&lt;br&gt;aromatics is limited, our results indicate that aromatics can strongly&lt;br&gt;influence tropospheric chemistry on a regional scale, most significantly&lt;br&gt;in East Asia.&lt;/p&gt;

scholarly journals Application of random forest regression to the calculation of gas-phase chemistry within the GEOS-Chem chemistry model v10

2018 ◽  
Author(s):  
Christoph A. Keller ◽  
Mat J. Evans
Keyword(s):  
Machine Learning ◽  
Random Forest ◽  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Random Forest Regression ◽  
Data Set ◽  
Gas Phase Chemistry ◽  
Chemical Conditions ◽  
Phase Chemistry ◽  
The Impact

Abstract. Atmospheric chemistry models are a central tool to study the impact of chemical constituents on the environment, vegetation and human health. These models are numerically intense, and previous attempts to reduce the numerical cost of chemistry solvers have not delivered transformative change. We show here the potential of a machine learning (in this case random forest regression) replacement for the gas-phase chemistry in atmospheric chemistry models. Our training data consists of one month (July 2013) of output of chemical conditions together with the model physical state, produced from the GEOS-Chem chemistry model (v10). From this data set we train random forest regression models to predict the concentration of each transported species after the integrator, based on the physical and chemical conditions before the integrator. The choice of prediction type has a strong impact on the skill of the regression model. We find best results from predicting the change in concentration for long-lived species and the absolute concentration for short-lived species. We also find improvements from a simple implementation of chemical families (NOx = NO + NO2). We then implement the trained random forest predictors back into GEOS-Chem to replace the numerical integrator. The machine learning driven GEOS-Chem model compares well to the standard simulation. For O3, error from using the random forests grow slowly and after 5 days the normalised mean bias (NMB), root mean square error (RMSE) and R2 are 4.2 %, 35 %, 0.9 respectively; after 30 days the errors increase to 13 %, 67 %, 0.75. The biases become largest in remote areas such as the tropical Pacific where errors in the chemistry can accumulate with little balancing influence from emissions or deposition. Over polluted regions the model error is less than 10 % and has significant fidelity in following the time series of the full model. Modelled NOx shows similar features, with the most significant errors occurring in remote locations far from recent emissions. For other species such as inorganic bromine species and short lived nitrogen species errors become large, with NMB, RMSE and R2 reaching >2100 % >400 %, <0.1 respectively. This proof-of-concept implementation is 85 % slower than the direct integration of the differential equations but optimisation and software engineering would allow substantial increases in speed. We discuss potential improvements in the implementation, some of its advantages from both a software and hardware perspective, its limitations and its applicability to operational air quality activities.

scholarly journals Methanol ice co-desorption as a mechanism to explain cold methanol in the gas-phase

2018 ◽  
Vol 612 ◽  
pp. A88 ◽  
Author(s):  
N. F. W. Ligterink ◽  
C. Walsh ◽  
R. G. Bhuin ◽  
S. Vissapragada ◽  
J. Terwisscha van Scheltinga ◽  
...  
Keyword(s):  
Gas Phase ◽  
Thermal Desorption ◽  
High Vacuum ◽  
Protoplanetary Disk ◽  
Ultra High Vacuum ◽  
Indirect Pathway ◽  
Cold Environments ◽  
Chemical Modelling ◽  
Phase Chemistry ◽  
The Impact

Context. Methanol is formed via surface reactions on icy dust grains. Methanol is also detected in the gas-phase at temperatures below its thermal desorption temperature and at levels higher than can be explained by pure gas-phase chemistry. The process that controls the transition from solid state to gas-phase methanol in cold environments is not understood. Aims. The goal of this work is to investigate whether thermal CO desorption provides an indirect pathway for methanol to co-desorb at low temperatures. Methods. Mixed CH3OH:CO/CH4 ices were heated under ultra-high vacuum conditions and ice contents are traced using RAIRS (reflection absorption IR spectroscopy), while desorbing species were detected mass spectrometrically. An updated gas-grain chemical network was used to test the impact of the results of these experiments. The physical model used is applicable for TW Hya, a protoplanetary disk in which cold gas-phase methanol has recently been detected. Results. Methanol release together with thermal CO desorption is found to be an ineffective process in the experiments, resulting in an upper limit of ≤ 7.3 × 10−7 CH3OH molecules per CO molecule over all ice mixtures considered. Chemical modelling based on the upper limits shows that co-desorption rates as low as 10−6 CH3OH molecules per CO molecule are high enough to release substantial amounts of methanol to the gas-phase at and around the location of the CO thermal desorption front in a protoplanetary disk. The impact of thermal co-desorption of CH3OH with CO as a grain-gas bridge mechanism is compared with that of UV induced photodesorption and chemisorption.

scholarly journals Comparison of tropospheric gas-phase chemistry schemes for use within global models

2009 ◽  
Vol 9 (5) ◽  
pp. 1831-1845 ◽  
Author(s):  
K. M. Emmerson ◽  
M. J. Evans
Keyword(s):  
Gas Phase ◽  
Transport Model ◽  
Regional Scale ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Model Framework ◽  
Transport Models ◽  
Global Models ◽  
Calculated Concentration ◽  
The Impact

Abstract. Methane and ozone are two important climate gases with significant tropospheric chemistry. Within chemistry-climate and transport models this chemistry is simplified for computational expediency. We compare the state of the art Master Chemical Mechanism (MCM) with six tropospheric chemistry schemes (CRI-reduced, GEOS-CHEM and a GEOS-CHEM adduct, MOZART-2, TOMCAT and CBM-IV) that could be used within composition transport models. We test the schemes within a box model framework under conditions derived from a composition transport model and from field observations from a regional scale pollution event. We find that CRI-reduced provides much skill in simulating the full chemistry, yet with greatly reduced complexity. We find significant variations between the other chemical schemes, and reach the following conclusions. 1) The inclusion of a gas phase N2O5+H2O reaction in one scheme and not others is a large source of uncertainty in the inorganic chemistry. 2) There are significant variations in the calculated concentration of PAN between the schemes, which will affect the long range transport of reactive nitrogen in global models. 3) The representation of isoprene chemistry differs hugely between the schemes, leading to significant uncertainties on the impact of isoprene on composition. 4) Differences are found in NO3 concentrations in the nighttime chemistry. Resolving these four issues through further investigative laboratory studies will reduce the uncertainties within the chemical schemes of global tropospheric models.

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