scholarly journals Iodine's impact on tropospheric oxidants: a global model study in GEOS-Chem

2016 ◽  
Vol 16 (2) ◽  
pp. 1161-1186 ◽  
Author(s):  
T. Sherwen ◽  
M. J. Evans ◽  
L. J. Carpenter ◽  
S. J. Andrews ◽  
R. T. Lidster ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Transport Model ◽  
Heterogeneous Reactions ◽  
Polar Regions ◽  
Chemical Transport Model ◽  
Model Study ◽  
Sensitivity Studies ◽  
Tropospheric O3 ◽  
Iodine Chemistry ◽  
Inorganic Iodine

Abstract. We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry, and simplified higher iodine oxide (I2OX, X = 2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent iodine oxide (IO) observations, the simulation shows an average bias of  ∼ +90 % with available surface observations in the marine boundary layer (outside of polar regions), and of  ∼ +73 % within the free troposphere (350 hPa  <  p  <  900 hPa) over the eastern Pacific. Iodine emissions (3.8 Tg yr−1) are overwhelmingly dominated by the inorganic ocean source, with 76 % of this emission from hypoiodous acid (HOI). HOI is also found to be the dominant iodine species in terms of global tropospheric IY burden (contributing up to 70 %). The iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0 %) compared to standard GEOS-Chem (v9-2). The iodine-driven OX loss rate1 (748 Tg OX yr−1) is due to photolysis of HOI (78 %), photolysis of OIO (21 %), and reaction between IO and BrO (1 %). Increases in global mean OH concentrations (1.8 %) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range of parameters and conclude that the simulation is sensitive to choices in parametrization of heterogeneous uptake, ocean surface iodide, and I2OX (X = 2, 3, 4) photolysis. The new iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine- and iodine-driven tropospheric O3 burden decrease of 14.4 % compared to a simulation without iodine and bromine chemistry in the model, and a small increase in OH (1.8 %). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models. 1 Here OX is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN  =  peroxyacetyl nitrate, PPN  =  peroxypropionyl nitrate, MPN  =  methyl peroxy nitrate, and MPN  =  peroxymethacryloyl nitrate.

scholarly journals Iodine's impact on tropospheric oxidants: a global model study in GEOS-Chem

2015 ◽  
Vol 15 (15) ◽  
pp. 20957-21023 ◽  
Author(s):  
T. Sherwen ◽  
M. J. Evans ◽  
L. J. Carpenter ◽  
S. J. Andrews ◽  
R. T. Lidster ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Transport Model ◽  
Heterogeneous Reactions ◽  
Polar Regions ◽  
Chemical Transport Model ◽  
Model Study ◽  
Sensitivity Studies ◽  
Tropospheric O3 ◽  
Iodine Chemistry ◽  
Inorganic Iodine

Abstract. We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry and simplified higher iodine oxide (I2OX, X = 2, 3, 4) chemistry, photolysis, deposition and parametrised heterogeneous reactions. In comparisons with recent Iodine Oxide (IO) observations the iodine simulation shows an average bias of ~+66 % available surface observations in the marine boundary layer (outside of polar regions), and of ~+73 % within the free troposphere (350 < hPa < 900) over the eastern Pacific. Iodine emissions (3.8 Tg yr−1) are overwhelmingly dominated by the inorganic ocean source, with 76 % of this emission from Hypoiodous acid (HOI). HOI is also found to be the dominant iodine species in terms of global tropospheric IY burden (contributing up to 70 %). The iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0 %) compared to standard GEOS-Chem (v9-2). The iodine-driven OX loss rate (748 Tg OX yr−1) is by photolysis of HOI (78 %), photolysis of OIO (21 %), and reaction of IO and BrO (1 %). Increases in global mean OH concentrations (1.8 %) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range parameters and conclude that the simulation is sensitive to choices in parameterisation of heterogeneous uptake, ocean surface iodide, and I2OX (X = 2, 3, 4) photolysis. The new iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine and iodine driven tropospheric O3 burden decrease of 14.4 % compared to a simulation without iodine and bromine chemistry in the model. This is a significant impact and so halogen chemistry needs to be considered in climate and air quality models.

scholarly journals Importance of reactive halogens in the tropical marine atmosphere: A regional modelling study using WRF-Chem

2017 ◽  
Author(s):  
Alba Badia ◽  
Claire E. Reeves ◽  
Alex R. Baker ◽  
Alfonso Saiz-Lopez ◽  
Rainer Volkamer ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Transport Model ◽  
Model Performance ◽  
Sea Salt ◽  
Heterogeneous Reactions ◽  
Regional Modelling ◽  
Mixing Ratios ◽  
Inorganic Iodine ◽  
The Impact

Abstract. This study investigates the impact of halogens on atmospheric chemistry in the tropical troposphere and explores the sensitivity of this to uncertainties in the fluxes of halogens to the atmosphere and the chemical processing. To do this the regional chemistry transport model WRF-Chem has been extended, for the first time, to include halogen chemistry (bromine, chlorine and iodine chemistry), including heterogeneous recycling reactions involving sea-salt aerosol and other particles, reactions of Br with volatile organic compounds (VOCs), along with oceanic emissions of halocarbons, VOCs and inorganic iodine. The study focuses on the tropical East Pacific using field observations from the TORERO campaign (January–February 2012) to evaluate the model performance. Including all the new processes, the model does a reasonable job reproducing the observed mixing ratios of BrO and IO, albeit with some discrepancies, some of which can be attributed to difficulties in the model's ability to reproduce the observed halocarbons. This is somewhat expected given the large uncertainties in the air-sea fluxes of the halocarbons in a region where there are few observations of seawater concentrations. We see a considerable impact on the Bry partitioning when heterogeneous chemistry is included, with a greater proportion of the Bry in active forms such as BrO, HOBr and dihalogens. Including debromination of sea-salt increases BrO slightly throughout the free troposphere, but in the tropical marine boundary layer, where the sea-salt particles are plentiful and relatively acidic, debromination leads to overestimation of the observed BrO. However, it should be noted that the modelled BrO was extremely sensitive to the inclusion of reactions between Br and the VOCs, which convert Br to HBr, a far less reactive form of Bry. Excluding these reactions leads to modelled BrO mixing ratios greater than observed. The reactions between Br and aldehydes were found to be particularly important, despite the model underestimating the amount of aldehydes observed in the atmosphere. There are only small changes to Iy partitioning and IO when the heterogeneous reactions, primarly on sea-salt, are included. Our model results show that the tropospheric Ox loss due to halogens is 31 %. This loss is mostly due to I (16 %) and Br (14 %) and it is in good agreement with other estimates from state-of-the-art atmospheric chemistry models.

scholarly journals Effects of tropospheric emissions on global tropospheric ozone distribution: A CTM simulation study

2017 ◽  
Author(s):  
Kuo-Ying Wang
Keyword(s):  
Boundary Layer ◽  
Northern Hemisphere ◽  
Biomass Burning ◽  
Tropospheric Ozone ◽  
Amazon Basin ◽  
Marine Boundary Layer ◽  
Transport Model ◽  
Polar Regions ◽  
No Emission ◽  
Tropospheric O3

In this work, we examined the effect of tropospheric emissions on tropospheric ozone (O3) by conducting three-dimensional (3D) chemistry transport model (CTM) simulations. For the control run, the CTM model simulates tropospheric O3 levels with a complete set of anthropogenic, biomass burning, and vegetation emissions [8]. For the no-emission simulation, all anthropogenic, biomass burning, and vegetation emissions were turned off. Comparisons of results from these two simulations exhibit the emission impacts on the tropospheric O3. In the no-emission simulation, distinctive low surface O3 with concentrations less than 5 ppbv prevail over the Amazon basin, tropical South America, tropical South Africa, Southeast Asia. Transport of air from these land areas downwind contributes to the low&nbsp;O3 over the remote marine boundary layer. In contrast, elevated&nbsp;O3 levels over the extra-tropical remote marine boundary layer are less supported by the anthropogenic and biomass burning emissions but more sustained by the downward transport of&nbsp;O3 from the stratosphere. These results demonstrate that the northern hemisphere continental areas (north of 30◦N ), polar regions, and tropical continental regions are more sensitive to the tropospheric emissions. The northern hemisphere winter is mostly dominated by the stratospheric processes, while the tropospheric emissions dominate over the southern hemisphere tropical continental areas from tropics to 30◦S latitudinal bands. The northern hemisphere continental regions are increasingly dominated by tropospheric emissions from spring, to reach maxima in summer, and started to reduce in autumn months.

scholarly journals A global off-line model of size-resolved aerosol microphysics: I. Model development and prediction of aerosol properties

2005 ◽  
Vol 5 (8) ◽  
pp. 2227-2252 ◽  
Author(s):  
D. V. Spracklen ◽  
K. J. Pringle ◽  
K. S. Carslaw ◽  
M. P. Chipperfield ◽  
G. W. Mann
Keyword(s):  
Boundary Layer ◽  
Sulfuric Acid ◽  
Size Distribution ◽  
Marine Boundary Layer ◽  
Transport Model ◽  
Model Development ◽  
Aerosol Size Distribution ◽  
Chemical Transport Model ◽  
Cloud Processing ◽  
Nucleation Mechanisms

Abstract. A GLObal Model of Aerosol Processes (GLOMAP) has been developed as an extension to the TOMCAT 3-D Eulerian off-line chemical transport model. GLOMAP simulates the evolution of the global aerosol size distribution using a sectional two-moment scheme and includes the processes of aerosol nucleation, condensation, growth, coagulation, wet and dry deposition and cloud processing. We describe the results of a global simulation of sulfuric acid and sea spray aerosol. The model captures features of the aerosol size distribution that are well established from observations in the marine boundary layer and free troposphere. Modelled condensation nuclei (CN>3nm) vary between about 250–500 cm-3 in remote marine boundary layer regions and are generally in good agreement with observations. Modelled continental CN concentrations are lower than observed, which may be due to lack of some primary aerosol sources or the neglect of nucleation mechanisms other than binary homogeneous nucleation of sulfuric acid-water particles. Remote marine CN concentrations increase to around 2000–10 000 cm

scholarly journals Solar response in tropical stratospheric ozone: a 3-D chemical transport model study using ERA reanalyses

2011 ◽  
Vol 11 (24) ◽  
pp. 12773-12786 ◽  
Author(s):  
S. Dhomse ◽  
M. P. Chipperfield ◽  
W. Feng ◽  
J. D. Haigh
Keyword(s):  
Standard Model ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Chemical Transport ◽  
Stratospheric Aerosol ◽  
Data Sets ◽  
Chemical Transport Model ◽  
Model Simulations ◽  
Model Study ◽  
Significant Difference

Abstract. We have used an off-line 3-D chemical transport model (CTM) to investigate the 11-yr solar cycle response in tropical stratospheric ozone. The model is forced with European Centre for Medium-Range Weather Forecasts (ECMWF) (re)analysis (ERA-40/operational and ERA-Interim) data for the 1979–2005 time period. We have compared the modelled solar response in ozone to observation-based data sets that are constructed using satellite instruments such as Total Ozone Mapping Spectrometer (TOMS), Solar Backscatter UltraViolet instrument (SBUV), Stratospheric Aerosol and Gas Experiment (SAGE) and Halogen Occultation Experiment (HALOE). A significant difference is seen between simulated and observed ozone during the 1980s, which is probably due to inhomogeneities in the ERA-40 reanalyses. In general, the model with ERA-Interim dynamics shows better agreement with the observations from 1990 onwards than with ERA-40. Overall both standard model simulations are partially able to simulate a "double peak"-structured ozone solar response with a minimum around 30 km, and these are in better agreement with HALOE than SAGE-corrected SBUV (SBUV/SAGE) or SAGE-based data sets. In the tropical lower stratosphere (TLS), the modelled solar response with time-varying aerosols is amplified through aliasing with a volcanic signal, as the model overestimates ozone loss during high aerosol loading years. However, the modelled solar response with fixed dynamics and constant aerosols shows a positive signal which is in better agreement with SBUV/SAGE and SAGE-based data sets in the TLS. Our model simulations suggests that photochemistry contributes to the ozone solar response in this region. The largest model-observation differences occur in the upper stratosphere where SBUV/SAGE and SAGE-based data show a significant (up to 4%) solar response whereas the standard model and HALOE do not. This is partly due to a positive solar response in the ECMWF upper stratospheric temperatures which reduces the modelled ozone signal. The large positive upper stratospheric solar response seen in SBUV/SAGE and SAGE-based data can be reproduced in model runs with fixed dynamical fields (i.e. no inter-annual meteorological changes). As these runs effectively assume no long-term temperature changes (solar-induced or otherwise), it should provide an upper limit of the ozone solar response. Overall, full quantification of the solar response in stratospheric ozone is limited by differences in the observed data sets and by uncertainties in the solar response in stratospheric temperatures.

scholarly journals Evaluation of water vapour assimilation in the tropical upper troposphere and lower stratosphere by a chemical transport model

2016 ◽  
Vol 9 (9) ◽  
pp. 4355-4373 ◽  
Author(s):  
Swagata Payra ◽  
Philippe Ricaud ◽  
Rachid Abida ◽  
Laaziz El Amraoui ◽  
Jean-Luc Attié ◽  
...  
Keyword(s):  
Water Vapour ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Michelson Interferometer ◽  
Model Space ◽  
Global Scale ◽  
Chemical Transport Model ◽  
Data Set ◽  
Upper Troposphere ◽  
Sensitivity Studies

Abstract. The present analysis deals with one of the most debated aspects of the studies on the upper troposphere/lower stratosphere (UTLS), namely the budget of water vapour (H2O) at the tropical tropopause. Within the French project “Multiscale water budget in the upper troposphere and lower stratosphere in the TROpics” (TRO-pico), a global-scale analysis has been set up based on space-borne observations, models and assimilation techniques. The MOCAGE-VALENTINA assimilation tool has been used to assimilate the Aura Microwave Limb Sounder (MLS) version 3.3 H2O measurements within the 316–5 hPa range from August 2011 to March 2013 with an assimilation window of 1 h. Diagnostics based on observations minus analysis and forecast are developed to assess the quality of the assimilated H2O fields. Comparison with an independent source of H2O measurements in the UTLS based on the space-borne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) observations and with meteorological ARPEGE analyses is also shown. Sensitivity studies of the analysed fields have been performed by (1) considering periods when no MLS measurements are available and (2) using H2O data from another MLS version (4.2). The studies have been performed within three different spaces in time and space coincidences with MLS (hereafter referred to as MLS space) and MIPAS (MIPAS space) observations and with the model (model space) outputs and at three different levels: 121 hPa (upper troposphere), 100 hPa (tropopause) and 68 hPa (lower stratosphere) in January and February 2012. In the MLS space, the analyses behave consistently with the MLS observations from the upper troposphere to the lower stratosphere. In the model space, the analyses are wetter than the reference atmosphere as represented by ARPEGE and MLS in the upper troposphere (121 hPa) and around the tropopause (100 hPa), but are consistent with MLS and MIPAS in the lower stratosphere (68 hPa). In the MIPAS space, the sensitivity and the vertical resolution of the MIPAS data set at 121 and 100 hPa prevent assessment of the behaviour of the analyses at 121 and 100 hPa, particularly over intense convective areas as the South American, the African and the Maritime continents but, in the lower stratosphere (68 hPa), the analyses are very consistent with MIPAS. Sensitivity studies show the improvement on the H2O analyses in the tropical UTLS when assimilating space-borne measurements of better quality, particularly over the convective areas.

scholarly journals Heterogeneous reaction of HO<sub>2</sub> with airborne TiO<sub>2</sub> particles and its implication for climate change mitigation strategies

2017 ◽  
Author(s):  
Daniel R. Moon ◽  
Giorgio S. Taverna ◽  
Clara Anduix-Canto ◽  
Trevor Ingham ◽  
Martyn P. Chipperfield ◽  
...  
Keyword(s):  
Transport Model ◽  
Heterogeneous Reaction ◽  
Three Dimensional ◽  
Mitigation Strategies ◽  
Heterogeneous Reactions ◽  
Chemical Transport Model ◽  
Flow Tube ◽  
Tio2 Particles ◽  
The Impact ◽  
Change Mitigation

Abstract. One geoengineering mitigation strategy for global temperature rises resulting from the increased concentrations of greenhouse gases is to inject particles into the stratosphere to scatter solar radiation back to space, with TiO2 particles emerging as a possible candidate. Uptake coefficients of HO2, γ(HO2), onto sub-micrometre TiO2 particles were measured at room temperature and different relative humidities (RH) using an atmospheric pressure aerosol flow tube coupled to a sensitive HO2 detector. Values of γ(HO2) increased from 0.021 ± 0.001 to 0.036 ± 0.007 as the RH was increased from 11 % to 66 %, and the increase in γ(HO2) correlated with the number of monolayers of water surrounding the TiO2 particles. The impact of the uptake of HO2 onto TiO2 particles on stratospheric concentrations of HO2 and O3 was simulated using the TOMCAT three-dimensional chemical transport model. The model showed that by injecting the amount of TiO2 required to achieve the same cooling effect as the Mt. Pinatubo eruption, heterogeneous reactions between HO2 and TiO2 would have a negligible effect on stratospheric concentrations of HO2 and O3.

scholarly journals Global lightning NO<sub>x</sub> production estimated by an assimilation of multiple satellite data sets

2014 ◽  
Vol 14 (7) ◽  
pp. 3277-3305 ◽  
Author(s):  
K. Miyazaki ◽  
H. J. Eskes ◽  
K. Sudo ◽  
C. Zhang
Keyword(s):  
Satellite Data ◽  
Production Efficiency ◽  
Transport Model ◽  
Chemical System ◽  
No Production ◽  
Data Sets ◽  
Chemical Transport Model ◽  
Ozone Monitoring Instrument ◽  
Independent Observations ◽  
Sensitivity Studies

Abstract. The global source of lightning-produced NOx (LNOx) is estimated by assimilating observations of NO2, O3, HNO3, and CO measured by multiple satellite measurements into a chemical transport model. Included are observations from the Ozone Monitoring Instrument (OMI), Microwave Limb Sounder (MLS), Tropospheric Emission Spectrometer (TES), and Measurements of Pollution in the Troposphere (MOPITT) instruments. The assimilation of multiple chemical data sets with different vertical sensitivity profiles provides comprehensive constraints on the global LNOx source while improving the representations of the entire chemical system affecting atmospheric NOx, including surface emissions and inflows from the stratosphere. The annual global LNOx source amount and NO production efficiency are estimated at 6.3 Tg N yr−1 and 310 mol NO flash−1, respectively. Sensitivity studies with perturbed satellite data sets, model and data assimilation settings lead to an error estimate of about 1.4 Tg N yr−1 on this global LNOx source. These estimates are significantly different from those estimated from a parameter inversion that optimizes only the LNOx source from NO2 observations alone, which may lead to an overestimate of the source adjustment. The total LNOx source is predominantly corrected by the assimilation of OMI NO2 observations, while TES and MLS observations add important constraints on the vertical source profile. The results indicate that the widely used lightning parameterization based on the C-shape assumption underestimates the source in the upper troposphere and overestimates the peak source height by up to about 1 km over land and the tropical western Pacific. Adjustments are larger over ocean than over land, suggesting that the cloud height dependence is too weak over the ocean in the Price and Rind (1992) approach. The significantly improved agreement between the analyzed ozone fields and independent observations gives confidence in the performance of the LNOx source estimation.

scholarly journals Retrieving the vertical distribution of stratospheric OClO from Odin/OSIRIS limb-scattered sunlight measurements

2005 ◽  
Vol 5 (3) ◽  
pp. 2989-3046 ◽  
Author(s):  
P. Krecl ◽  
C. S. Haley ◽  
J. Stegman ◽  
S. M. Brohede ◽  
G. Berthet
Keyword(s):  
Transport Model ◽  
Polar Vortex ◽  
Optical Absorption Spectroscopy ◽  
Polar Regions ◽  
Atmospheric Conditions ◽  
Chemical Transport Model ◽  
Austral Spring ◽  
Data Set ◽  
Spectral Window ◽  
Window Selection

Abstract. The first vertical profiles of stratospheric OClO retrieved from Odin/OSIRIS limb-scattered sunlight radiances are presented. The retrieval method is based on a two-step approach, using differential optical absorption spectroscopy combined with the maximum a posteriori estimator. The details of the spectral window selection, spectral corrections and inversion technique are discussed. The results show that OClO can be detected inside the South polar vortex region between about 12 and 20 km altitude with a 2–5 km height resolution and an estimated retrieval error better than 60% at the peak. OClO concentrations are consistent with chemical transport model simulations and show the expected relation to the atmospheric conditions in the lower stratosphere in the austral spring 2002. This unique data set of OClO profiles is very promising to study the stratospheric chlorine activation in both polar regions.

scholarly journals Global tropospheric halogen (Cl, Br, I) chemistry and its impact on oxidants

2021 ◽  
Author(s):  
Xuan Wang ◽  
Daniel J. Jacob ◽  
William Downs ◽  
Shuting Zhai ◽  
Lei Zhu ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Transport Model ◽  
Ph Dependence ◽  
Primary Source ◽  
Mixing Ratio ◽  
Chemical Transport Model ◽  
Oxidation Of Methane ◽  
Aircraft Observations ◽  
Chlorine Radicals ◽  
Global Mean

Abstract. We present an updated mechanism for tropospheric halogen (Cl + Br + I) chemistry in the GEOS-Chem global atmospheric chemical transport model and apply it to investigate halogen radical cycling and implications for tropospheric oxidants. Improved representation of HOBr heterogeneous chemistry and its pH dependence in our simulation leads to less effective recycling and mobilization of bromine radicals, and enables the model to include mechanistic sea salt aerosol debromination without generating excessive BrO. The resulting global mean tropospheric BrO mixing ratio is 0.19 ppt, lower than previous versions of GEOS-Chem. Model BrO shows variable consistency and biases in comparison to surface and aircraft observations in marine air, which are often near or below the detection limit. The model underestimates the daytime measurements of Cl2 and BrCl from the ATom aircraft campaign over the Pacific and Atlantic, which if correct would imply a very large missing primary source of chlorine radicals. Model IO is highest in the marine boundary layer and uniform in the free troposphere, with a global mean tropospheric mixing ratio of 0.08 ppt, and shows consistency with surface and aircraft observations. The modeled global mean tropospheric concentration of Cl atoms is 630 cm−3, contributing 0.8 % of the global oxidation of methane, 14 % of ethane, 8 % of propane, and 7 % of higher alkanes. Halogen chemistry decreases the global tropospheric burden of ozone by 11 %, NOx by 6 %, and OH by 4 %. Most of the ozone decrease is driven by iodine-catalyzed loss. The resulting GEOS-Chem ozone simulation is unbiased in the Southern Hemisphere but too low in the Northern Hemisphere.

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