scholarly journals On the vertical distribution of boundary layer halogens over coastal Antarctica: implications for O<sub>3</sub>, HO<sub>x</sub>, NO<sub>x</sub> and the Hg lifetime

2008 ◽  
Vol 8 (4) ◽  
pp. 887-900 ◽  
Author(s):  
A. Saiz-Lopez ◽  
J. M. C. Plane ◽  
A. S. Mahajan ◽  
P. S. Anderson ◽  
S. J.-B. Bauguitte ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Distribution ◽  
Transport Model ◽  
Current Knowledge ◽  
Sea Salt ◽  
Chemical Transport Model ◽  
Sea Salt Aerosol ◽  
Iodine Chemistry ◽  
The Antarctic ◽  
The Vertical Distribution

Abstract. A one-dimensional chemical transport model has been developed to investigate the vertical gradients of bromine and iodine compounds in the Antarctic coastal boundary layer (BL). The model has been applied to interpret recent year-round observations of iodine and bromine monoxides (IO and BrO) at Halley Station, Antarctica. The model requires an equivalent I atom flux of ~1010 molecule cm−2 s−1 from the snowpack in order to account for the measured IO levels, which are up to 20 ppt during spring. Using the current knowledge of gas-phase iodine chemistry, the model predicts significant gradients in the vertical distribution of iodine species. However, recent ground-based and satellite observations of IO imply that the radical is well-mixed in the Antarctic boundary layer, indicating a longer than expected atmospheric lifetime for the radical. This can be modelled by including photolysis of the higher iodine oxides (I2O2, I2O3, I2O4 and I2O5), and rapid recycling of HOI and INO3 through sea-salt aerosol. The model also predicts significant concentrations (up to 25 ppt) of I2O5 in the lowest 10 m of the boundary layer. Heterogeneous chemistry involving sea-salt aerosol is also necessary to account for the vertical profile of BrO. Iodine chemistry causes a large increase (typically more than 3-fold) in the rate of O3 depletion in the BL, compared with bromine chemistry alone. Rapid entrainment of O3 from the free troposphere appears to be required to account for the observation that on occasion there is little O3 depletion at the surface in the presence of high concentrations of IO and BrO. The halogens also cause significant changes to the vertical profiles of OH and HO2 and the NO2/NO ratio. The average Hg0 lifetime against oxidation is also predicted to be about 10 h during springtime. An important result from the model is that very large fluxes of iodine precursors into the boundary layer are required to account for the observed levels of IO. The mechanisms which cause these emissions are unknown. Overall, our results show that halogens profoundly influence the oxidizing capacity of the Antarctic troposphere.

scholarly journals On the vertical distribution of boundary layer halogens over coastal Antarctica: implications for O<sub>3</sub>, HO<sub>x</sub>, NO<sub>x</sub> and the Hg lifetime

2007 ◽  
Vol 7 (4) ◽  
pp. 9385-9417 ◽  
Author(s):  
A. Saiz-Lopez ◽  
J. M. C. Plane ◽  
A. S. Mahajan ◽  
P. S. Anderson ◽  
S. J.-B. Bauguitte ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Distribution ◽  
Transport Model ◽  
Current Knowledge ◽  
Sea Salt ◽  
Chemical Transport Model ◽  
Sea Salt Aerosol ◽  
Iodine Chemistry ◽  
The Antarctic ◽  
The Vertical Distribution

Abstract. A one-dimensional chemical transport model has been developed to investigate the vertical gradients of bromine and iodine compounds in the Antarctic coastal boundary layer. The model has been applied to interpret recent year-round observations of iodine and bromine monoxides (IO and BrO) at Halley Station, Antarctica. The model requires an equivalent I atom flux of ~109 molecule cm−2 s−1 from the snowpack in order to account for the measured IO levels, which are up to 20 ppt during spring. Using the current knowledge of gas-phase iodine chemistry, the model predicts significant gradients in the vertical distribution of iodine species. However, recent ground-based and satellite observations of IO imply that the radical is well-mixed in the boundary layer, indicating a longer than expected atmospheric lifetime for the radical. This can be modelled by including photolysis of the higher iodine oxides (I2O2, I2O3, I2O4 and I2O5), and rapid recycling of HOI and INO3 through sea-salt aerosol. The model also predicts significant concentrations (up to 25 ppt) of I2O5 in the lowest 10 m of the boundary layer, which could lead to the formation of ultrafine iodine oxide aerosols. Heterogeneous chemistry involving sea-salt aerosol is also necessary to account for the vertical profile of BrO. Iodine chemistry causes a large increase (typically more than 3-fold) in the rate of O3 depletion in the BL, compared with bromine chemistry alone. Rapid entrainment of O3 from the free troposphere is required to account for the observation that on occasion there is little O3 depletion at the surface in the presence of high concentrations of IO and BrO. The halogens also cause significant changes to the vertical profiles of HO and HO2 and the NO2/NO ratio. The average Hg0 lifetime against oxidation is also predicted to be about 10 h during springtime. Overall, our results show that halogens profoundly influence the oxidizing capacity of the Antarctic troposphere.

scholarly journals Modeling and evaluation of the global sea-salt aerosol distribution: sensitivity to size-resolved and sea-surface temperature dependent emission schemes

2013 ◽  
Vol 13 (23) ◽  
pp. 11735-11755 ◽  
Author(s):  
M. Spada ◽  
O. Jorba ◽  
C. Pérez García-Pando ◽  
Z. Janjic ◽  
J. M. Baldasano
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Transport Model ◽  
Surface Concentration ◽  
Sea Salt ◽  
Sea Surface ◽  
Chemical Transport Model ◽  
Sea Salt Aerosol ◽  
Aerosol Distribution ◽  
Mass Load

Abstract. One of the major sources of uncertainty in model estimates of the global sea-salt aerosol distribution is the emission parameterization. We evaluate a new sea-salt aerosol life cycle module coupled to the online multiscale chemical transport model NMMB/BSC-CTM. We compare 5 yr global simulations using five state-of-the-art sea-salt open-ocean emission schemes with monthly averaged coarse aerosol optical depth (AOD) from selected AERONET sun photometers, surface concentration measurements from the University of Miami's Ocean Aerosol Network, and measurements from two NOAA/PMEL cruises (AEROINDOEX and ACE1). Model results are highly sensitive to the introduction of sea-surface-temperature (SST)-dependent emissions and to the accounting of spume particles production. Emission ranges from 3888 Tg yr−1 to 8114 Tg yr−1, lifetime varies between 7.3 h and 11.3 h, and the average column mass load is between 5.0 Tg and 7.2 Tg. Coarse AOD is reproduced with an overall correlation of around 0.5 and with normalized biases ranging from +8.8% to +38.8%. Surface concentration is simulated with normalized biases ranging from −9.5% to +28% and the overall correlation is around 0.5. Our results indicate that SST-dependent emission schemes improve the overall model performance in reproducing surface concentrations. On the other hand, they lead to an overestimation of the coarse AOD at tropical latitudes, although it may be affected by uncertainties in the comparison due to the use of all-sky model AOD, the treatment of water uptake, deposition and optical properties in the model and/or an inaccurate size distribution at emission.

scholarly journals Modeling and evaluation of the global sea-salt aerosol distribution: sensitivity to emission schemes and resolution effects at coastal/orographic sites

2013 ◽  
Vol 13 (5) ◽  
pp. 11597-11657 ◽  
Author(s):  
M. Spada ◽  
O. Jorba ◽  
C. Perez ◽  
Z. Janjic ◽  
J. M. Baldasano
Keyword(s):  
High Resolution ◽  
Transport Model ◽  
Scale Effects ◽  
Surface Concentration ◽  
Sea Salt ◽  
Complex Topography ◽  
Chemical Transport Model ◽  
Sea Salt Aerosol ◽  
Mass Load ◽  
Wide Range

Abstract. We investigate two of the major sources of uncertainty in the model estimation of the global distribution of sea-salt aerosol, i.e. the sensitivity to the emission parameterization and the influence of model resolution in coastal regions characterized by complex topography and/or steep orographic barriers where some observation sites are located. We evaluate a new sea-salt aerosol lifecycle module implemented within the online chemical transport model NMMB/BSC-CTM. Because of its multiscale core, the model is able to cover a wide range of scales. Global simulations using four state-of-the-art sea-salt emission schemes are evaluated against monthly-averaged aerosol optical depth (AOD) from selected AERONET Sun photometers, surface concentration measurements from the University of Miami's Ocean Aerosol Network and measurements from two NOAA/PMEL cruises (AEROINDOEX and ACE1). The model results are highly sensitive to the introduction of SST-dependent emissions and to the accounting of spume particles production. Depending on emission scheme, annual emissions range from 4312.9 Tg to 8979.7 Tg in the 2006. Sea-salt lifetime varies between 7.7 h and 12.0 h and the annual mean column mass load is between 5.9 Tg and 7.9 Tg. Observed coarse AOD monthly averages are reproduced with an overall correlation around 0.8 (a correlation of 0.6 is produced when applying the SST dependent scheme). Although monthly-averaged surface concentrations are overall in good agreement with the observations, there is a subset of coastal sites surrounded by complex topography where the global model overestimates by a factor of 2 or more. Using regional high-resolution simulations, we show that these large errors are mostly due to the global model's inability to capture local scale effects. In New Zeland, the increase in resolution produces a significant decrease of surface concentrations (up to 40%) – due to changes in the wind circulation and precipitation driven by the orographic barrier – which is in close agreement with surface concentration monthly climatologies measured by University of Miami stations in the region (Baring Head, Chatam Island and Inverncargill). The observed climatological precipitation in this area is well reproduced by the model at high resolution, while it is strongly underestimated when employing coarser scales. Our results outline that caution may be taken when evaluating and/or constraining coarse global sea-salt simulations with observations around coastal/orographic sites.

scholarly journals Seasonal features and origins of carbonaceous aerosols at Syowa Station, coastal Antarctica

2019 ◽  
Vol 19 (11) ◽  
pp. 7817-7837 ◽  
Author(s):  
Keiichiro Hara ◽  
Kengo Sudo ◽  
Takato Ohnishi ◽  
Kazuo Osada ◽  
Masanori Yabuki ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Transport Model ◽  
Model Simulation ◽  
Chemical Transport ◽  
Chemical Transport Model ◽  
Backward Trajectory ◽  
Syowa Station ◽  
The Antarctic ◽  
Measurement Period

Abstract. We have measured black carbon (BC) concentrations at Syowa Station, Antarctica, since February 2005. The measured BC concentrations in 2005–2016 were corrected to equivalent BC (EBC) concentrations using Weingartner's method. Seasonal features of EBC concentrations, long-range transport from mid-latitudes to the Antarctic coast, and their origins were characterized. Results show that daily median EBC concentrations were below the detection limit (0.2 ng m−3) to 63.8 ng m−3 at Syowa Station (median, 1.8 ng m−3; mean, 2.7 ng m−3 during the measurement period of February 2005–December 2016). Although seasonal features and year-to-year variations in EBC concentrations were observed, no long-term trend of EBC concentrations was clear during our measurement period. Seasonal features of EBC concentrations showed a spring maximum during September–October at Syowa Station. To elucidate EBC transport processes, origins, and the potential source area (PSA), we compared EBC data to backward trajectory analysis and chemical transport model simulation. From comparison with backward trajectory, high EBC concentrations were found in air masses from the marine boundary layer. This finding implies that transport via the marine boundary layer was the most important transport pathway to EBC concentrations at Antarctic coasts. Some EBC was supplied to the Antarctic region by transport via the upper free troposphere. Chemical transport model simulation demonstrated that the most important origins and PSA of EBC at Syowa Station were biomass burning in South America and southern Africa. Fossil fuel combustion in South America and southern Africa also have important contributions. The absorption Ångström exponent (AAE) showed clear seasonal features with 0.5–1.0 during April–October and maximum (1.0–1.5) in December–February. The AAE features might be associated with organic aerosols and mixing states of EBC.

scholarly journals The impact of snow nitrate photolysis on boundary layer chemistry and the recycling and redistribution of reactive nitrogen across Antarctica in a global chemical transport model

2015 ◽  
Vol 15 (13) ◽  
pp. 18963-19015
Author(s):  
M. C. Zatko ◽  
L. Geng ◽  
B. Alexander ◽  
E. D. Sofen ◽  
K. Klein
Keyword(s):  
Boundary Layer ◽  
Transport Model ◽  
Ice Core ◽  
Ice Cores ◽  
Reactive Nitrogen ◽  
Nitrogen Recycling ◽  
Chemical Transport Model ◽  
Antarctic Continent ◽  
Δ 15N ◽  
The Antarctic

Abstract. The formation and recycling of reactive nitrogen (NO, NO2, HONO) at the air-snow interface has implications for air quality and the oxidation capacity of the atmosphere in snow-covered regions. Nitrate(NO3-) photolysis in snow provides a source of oxidants (e.g., hydroxyl radical, ozone) and oxidant precursors (e.g., nitrogen oxides) to the overlying boundary layer, and disturbs the preservation of NO3- in ice cores. We have incorporated the photolysis of Antarctic snow NO3- into a global chemical transport model (GEOS-Chem) to examine the implications of snow NO3- photolysis for boundary layer chemistry, the recycling and redistribution of reactive nitrogen across the Antarctic continent, and the preservation of ice-core NO3- in Antarctic ice cores. The calculated potential flux of snow-sourced NOx in Antarctica (0.5–7.8 × 108 molec cm-2 s-1) and calculated e-folding depths of UV actinic flux in snowpack (24–69 cm) are comparable to observations. Snow-sourced NOx increases mean austral summer boundary layer mixing ratios of total nitrate (HNO3 + NO3-), NOx, OH, and O3 in Antarctica by a factor of up to 32, 38, 7, and 2, respectively, in the model. Model results also suggest that NO3- can be recycled between the air and snow multiple times and that NO3- can remain in the snow photic zone for at least 7.5 years on the East Antarctic plateau. The fraction of photolysis-driven loss of NO3- from the snow is ∼ 0.99 on the East Antarctic plateau, while areas of wind convergence (e.g., over the Ronne Ice Shelf) have a net gain of NO3- due to redistribution of snow-sourced reactive nitrogen across the Antarctic continent. The modeled enrichment in ice-core δ 15N(NO3-) due to photolysis-driven loss of snow NO3- ranges from 0 to 363 ‰ and the magnitudes of the spatial trends are consistent with δ 15N(NO3-) observations, suggesting that the spatial variability in snow δ 15N(NO3-) across the Antarctic continent is determined mainly by the degree of photolysis-driven loss of snow NO3-. Further, there is a strong relationship between the degree of photolysis-driven loss of snow NO3- and the degree of nitrogen recycling between the air and snow, suggesting that ice-core δ 15N(NO3-) observations can be used to assess the degree of nitrogen recycling and loss over much of Antarctica and aid in the interpretation of ice-core NO3- in terms of past atmospheric variability of reactive nitrogen.

scholarly journals Estimation of Volcanic Ash Emissions Using Trajectory-Based 4D-Var Data Assimilation

2016 ◽  
Vol 144 (2) ◽  
pp. 575-589 ◽  
Author(s):  
S. Lu ◽  
H. X. Lin ◽  
A. W. Heemink ◽  
G. Fu ◽  
A. J. Segers
Keyword(s):  
Data Assimilation ◽  
Vertical Distribution ◽  
Volcanic Ash ◽  
Transport Model ◽  
Volcanic Eruptions ◽  
Emission Rates ◽  
Plume Height ◽  
Ill Posed ◽  
Total Difference ◽  
The Vertical Distribution

Abstract Volcanic ash forecasting is a crucial tool in hazard assessment and operational volcano monitoring. Emission parameters such as plume height, total emission mass, and vertical distribution of the emission plume rate are essential and important in the implementation of volcanic ash models. Therefore, estimation of emission parameters using available observations through data assimilation could help to increase the accuracy of forecasts and provide reliable advisory information. This paper focuses on the use of satellite total-ash-column data in 4D-Var based assimilations. Experiments show that it is very difficult to estimate the vertical distribution of effective volcanic ash injection rates from satellite-observed ash columns using a standard 4D-Var assimilation approach. This paper addresses the ill-posed nature of the assimilation problem from the perspective of a spurious relationship. To reduce the influence of a spurious relationship created by a radiate observation operator, an adjoint-free trajectory-based 4D-Var assimilation method is proposed, which is more accurate to estimate the vertical profile of volcanic ash from volcanic eruptions. The method seeks the optimal vertical distribution of emission rates of a reformulated cost function that computes the total difference between simulated and observed ash columns. A 3D simplified aerosol transport model and synthetic satellite observations are used to compare the results of both the standard method and the new method.

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 Inorganic bromine in the marine boundary layer: a critical review

2003 ◽  
Vol 3 (3) ◽  
pp. 2963-3050 ◽  
Author(s):  
R. Sander ◽  
W. C. Keene ◽  
A. A. P. Pszenny ◽  
R. Arimoto ◽  
G. P. Ayers ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Gas Phase ◽  
Marine Boundary Layer ◽  
Sea Water ◽  
Ocean Surface ◽  
Sea Salt ◽  
Future Research ◽  
Laboratory Studies ◽  
Model Calculations ◽  
Sea Salt Aerosol

Abstract. The cycling of inorganic bromine in the marine boundary layer (mbl) has received increased attention in recent years. Bromide, a constituent of sea water, is injected into the atmosphere in association with sea-salt aerosol by breaking waves on the ocean surface. Measurements reveal that supermicrometer sea-salt aerosol is depleted in bromine by about 50% relative to conservative tracers, whereas marine submicrometer aerosol is often enriched in bromine. Model calculations, laboratory studies, and field observations strongly suggest that these depletions reflect the chemical transformation of particulate bromide to reactive inorganic gases that influence the processing of ozone and other important constituents of marine air. However, currently available techniques cannot reliably quantify many \\chem{Br}-containing compounds at ambient concentrations and, consequently, our understanding of inorganic Br cycling over the oceans and its global significance are uncertain. To provide a more coherent framework for future research, we have reviewed measurements in marine aerosol, the gas phase, and in rain. We also summarize sources and sinks, as well as model and laboratory studies of chemical transformations. The focus is on inorganic bromine over the open oceans, excluding the polar regions. The generation of sea-salt aerosol at the ocean surface is the major tropospheric source producing about 6.2 Tg/a of bromide. The transport of  Br from continents (as mineral aerosol, and as products from biomass-burning and fossil-fuel combustion) can be of local importance. Transport of degradation products of long-lived Br-containing compounds from the stratosphere and other sources contribute lesser amounts. Available evidence suggests that, following aerosol acidification, sea-salt bromide reacts to form Br2 and BrCl that volatilize to the gas phase and photolyze in daylight to produce atomic Br and Cl. Subsequent transformations can destroy tropospheric ozone, oxidize dimethylsulfide (DMS) and hydrocarbons in the gas phase and S(IV) in aerosol solutions, and thereby potentially influence climate. The diurnal cycle of gas-phase \\Br and the corresponding particulate Br deficits are correlated. Higher values of Br in the gas phase during daytime are consistent with expectations based on photochemistry. Mechanisms that explain the widely reported accumulation of particulate Br in submicrometer aerosols are not yet understood. We expect that the importance of inorganic Br cycling will vary in the future as a function of both increasing acidification of the atmosphere (through anthropogenic emissions) and climate changes. The latter affects bromine cycling via meteorological factors including global wind fields (and the associated production of sea-salt aerosol), temperature, and relative humidity.

Sign in / Sign up

Export Citation Format

Share Document