scholarly journals Oxidation photochemistry in the Southern Atlantic boundary layer: unexpected deviations of photochemical steady state

2011 ◽  
Vol 11 (3) ◽  
pp. 7045-7093 ◽  
Author(s):  
Z. Hosaynali Beygi ◽  
H. Fischer ◽  
H. D. Harder ◽  
M. Martinez ◽  
R. Sander ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Atlantic Ocean ◽  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Air Pollutant ◽  
Photochemical Oxidant ◽  
Important Region ◽  
Atmospheric Observations ◽  
Oxidation Efficiency

Abstract. Ozone (O3) is a photochemical oxidant, an air pollutant and a greenhouse gas. As the main precursor of the hydroxyl radical (OH) it strongly affects the oxidation power of the atmosphere. The remote marine boundary layer (MBL) is considered an important region in terms of chemical O3 loss; however surface-based atmospheric observations are sparse and the photochemical processes are not well understood. To investigate the photochemistry under the clean background conditions of the Southern Atlantic Ocean, ship measurements of NO, NO2, O3, JNO2, J(O1D), HO2, OH, ROx and a range of meteorological parameters were carried out. The concentrations of NO and NO2 measured on board the French research vessel Marion-Dufresne (28° S–57° S, 46° W–34° E) in March 2007, are among the lowest yet observed. The data is evaluated for consistency with photochemical steady state (PSS) conditions, and the calculations indicate substantial deviations from PSS (Φ>1). The deviations observed under low NOx conditions (5–25 pptv) demonstrate a remarkable upward tendency in the Leighton ratio (used to characterize PSS) with increasing NOx mixing ratio and JNO2 intensity. It is a paradigm in atmospheric chemistry that OH largely controls the oxidation efficiency of the atmosphere. However, evidence is growing that for unpolluted low-NOx (NO + NO2) conditions the atmospheric oxidant budget is poorly understood. Nevertheless, for the very cleanest conditions, typical for the remote marine boundary layer, good model agreement with measured OH and HO2 radicals has been interpreted as accurate understanding of baseline photochemistry. Here we show that such agreement can be deceptive and that a yet unidentified oxidant is needed to explain the photochemical conditions observed at 40°–60° S over the Atlantic Ocean.

scholarly journals Oxidation photochemistry in the Southern Atlantic boundary layer: unexpected deviations of photochemical steady state

2011 ◽  
Vol 11 (16) ◽  
pp. 8497-8513 ◽  
Author(s):  
Z. Hosaynali Beygi ◽  
H. Fischer ◽  
H. D. Harder ◽  
M. Martinez ◽  
R. Sander ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Atlantic Ocean ◽  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Air Pollutant ◽  
Photochemical Oxidant ◽  
Important Region ◽  
Atmospheric Observations ◽  
Oxidation Efficiency

Abstract. Ozone (O3) is a photochemical oxidant, an air pollutant and a greenhouse gas. As the main precursor of the hydroxyl radical (OH) it strongly affects the oxidation power of the atmosphere. The remote marine boundary layer (MBL) is considered an important region in terms of chemical O3 loss; however surface-based atmospheric observations are sparse and the photochemical processes are not well understood. To investigate the photochemistry under the clean background conditions of the Southern Atlantic Ocean, ship measurements of NO, NO2, O3, JNO2, J(O1D), HO2, OH, ROx and a range of meteorological parameters were carried out. The concentrations of NO and NO2 measured on board the French research vessel Marion-Dufresne (28° S–57° S, 46° W–34° E) in March 2007, are among the lowest yet observed. The data is evaluated for consistency with photochemical steady state (PSS) conditions, and the calculations indicate substantial deviations from PSS (Φ>1). The deviations observed under low NOx conditions (5–25 pptv) demonstrate a remarkable upward tendency in the Leighton ratio (used to characterize PSS) with increasing NOx mixing ratio and JNO2 intensity. It is a paradigm in atmospheric chemistry that OH largely controls the oxidation efficiency of the atmosphere. However, evidence is growing that for unpolluted low-NOx (NO + NO2) conditions the atmospheric oxidant budget is poorly understood. Nevertheless, for the very cleanest conditions, typical for the remote marine boundary layer, good model agreement with measured OH and HO2 radicals has been interpreted as accurate understanding of baseline photochemistry. Here we show that such agreement can be deceptive and that a yet unidentified oxidant is needed to explain the photochemical conditions observed at 40°–60° S over the Atlantic Ocean.

scholarly journals Atmospheric bromoform at Mace Head, Ireland: seasonality and evidence for a peatland source

2005 ◽  
Vol 5 (11) ◽  
pp. 2927-2934 ◽  
Author(s):  
L. J. Carpenter ◽  
D. J. Wevill ◽  
S. O'Doherty ◽  
G. Spain ◽  
P. G. Simmonds
Keyword(s):  
Boundary Layer ◽  
Wind Direction ◽  
Marine Boundary Layer ◽  
Land Breeze ◽  
Peat Bogs ◽  
Mixing Ratios ◽  
The North ◽  
Prevailing Wind Direction ◽  
Atmospheric Observations ◽  
Summer Minimum

Abstract. In situ atmospheric observations of bromoform (CHBr3) made over a 2.5 year period at Mace Head, Ireland from May 2001- Dec 2003, including during the NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign, show broad maxima from spring until autumn and winter minima, with mixing ratios of 5.3+1.0 pptv (mid March - mid October) and 1.8+0.8 pptv (December-February). This indicates that, unlike CHCl3, which has a summer minimum and winter maximum at Mace Head, local biological sources of CHBr3 have a greater influence on the atmospheric data than photochemical decay during long-range transport. The emission sources are predominantly macroalgal, but we find evidence for a small terrestrial flux from peatland ecosystems, which so far has not been accounted for in the CHBr3 budget. Sharp increases in CHCl3 and CHBr3 concentrations and decreases in O3 concentrations occurred at night when the wind direction switched from an ocean- to a land-based sector (land breeze) and the wind speed dropped to below 5 ms-1. These observations infer a shallow atmospheric boundary layer with increased O3 deposition and concentration of local emissions of both CHCl3 and CHBr3. The ratio of ΔCHCl3/ΔCHBr3 varied strongly according to the prevailing wind direction; from 0.60+0.15 in south-easterly (100-170° and northerly (340-20°) air to 2.5+0.4 in north-easterly (40-70°) air. Of these land-sectors, the south-easterly air masses are likely to be strongly influenced by macroalgal beds along the coast and the emission ratios probably reflect those from seaweeds in addition to land sources. The north-easterly airmasses however had an immediate fetch inland, which locally is comprised of coastal peatland ecosystems (peat bogs and coastal conifer plantations), previously identified as being strong sources of atmospheric CHCl3 under these conditions. Although we cannot entirely rule out other local land or coastal sources, our observations also suggest peatland ecosystem emissions of CHBr3. We use correlations between CHCl3 and CHBr3 during the north-easterly land breeze events in conjunction with previous estimates of local wetland CHCl3 release to tentatively deduce a global wetland CHBr3 source of 20.4(0.4-948) Gg yr-1, which is approximately 7% of the total global source.

scholarly journals Surface fluxes of bromoform and dibromomethane over the tropical western Pacific inferred from airborne in situ measurements

2017 ◽  
Author(s):  
Liang Feng ◽  
Paul I. Palmer ◽  
Robyn Butler ◽  
Stephen J. Andrews ◽  
Elliot L. Atlas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Current Knowledge ◽  
A Priori ◽  
Surface Fluxes ◽  
Western Pacific ◽  
Study Region ◽  
The Western Pacific ◽  
Aircraft Data

Abstract. We infer surface fluxes of bromoform (CHBr3) and dibromoform (CH2Br2) from aircraft observations over the western Pacific using a tagged version of the GEOS-Chem global 3-D atmospheric chemistry model and a Maximum A Posteriori inverse model. The distribution of a priori ocean emissions of these gases are reasonably consistent with observed atmospheric mole fractions of CHBr3 (r = 0.62) and CH2Br2 (r = 0.38). These a priori emissions result in a positive model bias in CHBr3 peaking in the marine boundary layer, but capture observed values of CH2Br2 with no significant bias by virtue of its longer atmospheric lifetime. Using GEOS-Chem, we find that observed variations in atmospheric CHBr3 are determined equally by sources over the western Pacific and those outside the study region, but observed variations in CH2Br2 are determined mainly by sources outside the western Pacific. Numerical closed-loop experiments show that the spatial and temporal distribution of boundary layer aircraft data have the potential to substantially improve current knowledge of these fluxes, with improvements related to data density. Using the aircraft data, we estimate aggregated regional fluxes of 3.6 ± 0.3 × 108 g/month and 0.7 ± 0.1 × 108 g/month for CHBr3 and CH2Br2 over 130°–155° E and 0°–12° N, respectively, which represent reductions of 20–40 % and substantial spatial deviations from the a priori inventory. We find no evidence to support a robust linear relationship between CHBr3 and CH2Br2 oceanic emissions, as used by previous studies.

scholarly journals Observationally constrained analysis of sea salt aerosol in the marine atmosphere

2019 ◽  
Author(s):  
Huisheng Bian ◽  
Karl Froyd ◽  
Daniel M. Murphy ◽  
Jack Dibb ◽  
Mian Chin ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Model Simulation ◽  
In Situ Measurements ◽  
Sea Salt ◽  
Boreal Summer ◽  
Integrated Analysis ◽  
Marine Atmosphere

Abstract. Atmospheric sea salt plays important roles in marine cloud formation and atmospheric chemistry. We performed an integrated analysis of NASA GEOS model simulations run with the GOCART aerosol module, in situ measurements from the PALMS and SAGA instruments obtained during the NASA ATom campaign, and aerosol optical depth (AOD) measurements from AERONET Marine Aerosol Network (MAN) sun photometers and from MODIS satellite observations to better constrain sea salt in the marine atmosphere. ATom measurements and GEOS model simulation both show that sea salt concentrations over the Pacific and Atlantic oceans have a strong vertical gradient, varying up to four orders of magnitude from the marine boundary layer to free troposphere. The modeled residence times suggest that the lifetime of sea salt particles with dry diameter less than 3 μm is largely controlled by wet removal, followed next by turbulent process. During both boreal summer and winter, the GEOS simulated sea salt mass mixing ratios agree with SAGA measurements in the marine boundary layer (MBL) and with PALMS measurements above the MBL. However, comparison of AOD from GEOS with AERONET/MAN and MODIS aerosol retrievals indicated that the model underestimated AOD over the oceans where sea salt dominates. The apparent discrepancy of slightly overpredicted concentration and large underpredicted AOD could not be explained by biases in the model RH, which was found to be comparable to or larger than the in-situ measurements. This conundrum is at least partially explained by the sea salt size distribution; where the GEOS simulation has much less sea salt percentage-wise in the smaller particles than was observed by PALMS. Model sensitivity experiments indicated that the simulated sea salt is better correlated with measurements when the sea salt emission is calculated based on the friction velocity and with consideration of sea surface temperature dependence than that parameterized with the 10-m winds.

Aerosol size distributions and optical properties found in the marine boundary layer over the Atlantic Ocean

1990 ◽  
Vol 95 (D4) ◽  
pp. 3659 ◽  
Author(s):  
W. A. Hoppel ◽  
J. W. Fitzgerald ◽  
G. M. Frick ◽  
R. E. Larson ◽  
E. J. Mack
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Atlantic Ocean ◽  
Marine Boundary Layer ◽  
Size Distributions

scholarly journals Concentrations of OH and HO<sub>2</sub> radicals during NAMBLEX: measurements and steady state analysis

2005 ◽  
Vol 5 (6) ◽  
pp. 12403-12464 ◽  
Author(s):  
S. C. Smith ◽  
J. D. Lee ◽  
W. J. Bloss ◽  
G. P. Johnson ◽  
D. E. Heard
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Detection Limit ◽  
Diurnal Variation ◽  
Marine Boundary Layer ◽  
Chemical Conversion ◽  
Early Morning ◽  
Research Station ◽  
Solar Noon ◽  
Mean Concentration

Abstract. OH and HO2 concentrations were measured simultaneously at the Mace Head Atmospheric Research Station in the summer of 2002 during the NAMBLEX (North Atlantic Marine Boundary Layer EXperiment) field campaign. OH was measured by laser-induced fluorescence employing the FAGE (Fluorescence Assay by Gas Expansion) technique, with a mean daytime detection limit of 2.7×105 molecule cm−3 (5 min acquisition period; signal-to-noise ratio = 1). HO2 was detected as OH following its chemical conversion through addition of NO, with a mean detection limit of 4.4×106 molecule cm−3. The diurnal variation of OH was measured on 24 days, and that of HO2 on 17 days. The local solar noon OH concentrations ranged between (3–8)×106 molecule cm−3, with a 24 h mean concentration of 9.1×105 molecule cm−3. The local solar noon HO2 concentrations were (0.9–2.1)×108 molecule cm−3 (3.5–8.2 pptv), with a 24 h mean concentration of 4.2×107 molecule cm−3. HO2 radicals in the range (2–3)×107 molecule cm−3 were observed at night. During NAMBLEX, a comprehensive suite of supporting measurements enabled a detailed study of the behaviour of HOx radicals under primarily clean marine conditions. Case study periods highlight the typical radical levels observed under different conditions. Steady state expressions are used to calculate OH and HO2 concentrations and to evaluate the effect of different free-radical sources and sinks. The diurnally averaged calculated to measured OH ratio was 1.04±0.36, but the ratio displays a distinct diurnal variation, being less than 1 during the early morning and late afternoon/evening, and greater than 1 in the middle of the day. For HO2 there was an overprediction, with the agreement between calculated and measured concentrations improved by including reaction with measured IO and BrO radicals and uptake to aerosols. Increasing the concentration of IO radicals included in the calculations to above that measured by a DOAS instrument with an absorption path located mainly over the ocean, reflecting the domination of the inter-tidal region as an iodine source at Mace Head, led to further improvement. The results are compared with previous measurements at Mace Head, and elsewhere in the remote marine boundary layer.

scholarly journals Iodine oxide in the global marine boundary layer

2014 ◽  
Vol 14 (15) ◽  
pp. 22217-22243 ◽  
Author(s):  
C. Prados-Roman ◽  
C. A. Cuevas ◽  
T. Hay ◽  
R. P. Fernandez ◽  
A. S. Mahajan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Ozone Depletion ◽  
Marine Boundary Layer ◽  
Geographical Pattern ◽  
Mixing Ratios ◽  
Field Campaigns ◽  
Ozone Depletion Potential ◽  
Ubiquitous Presence ◽  
Inorganic Precursors

Abstract. Emitted mainly by the oceans, iodine is a halogen compound important for atmospheric chemistry due to its high ozone depletion potential and effect on the oxidizing capacity of the atmosphere. Here we present a comprehensive dataset of iodine oxide (IO) measurements in the open marine boundary layer (MBL) made during the Malaspina 2010 circumnavigation. Results show IO mixing ratios ranging from 0.4 to 1 pmol mol−1 and, complemented with additional field campaigns, this dataset confirms through observations the ubiquitous presence of reactive iodine chemistry in the global marine environment. We use a global model with organic (CH3I, CH2ICl, CH2I2 and CH2IBr) and inorganic (HOI and I2) iodine ocean emissions to investigate the contribution of the different iodine source gases to the budget of IO in the global MBL. In agreement with previous estimates, our results indicate that, globally averaged, the abiotic precursors contribute about 75% to the iodine oxide budget. However, this work reveals a strong geographical pattern in the contribution of organic vs. inorganic precursors to reactive iodine in the global MBL.

scholarly journals Chemistry, transport and dry deposition of trace gases in the boundary layer over the tropical Atlantic Ocean and the Guyanas during the GABRIEL field campaign

2007 ◽  
Vol 7 (2) ◽  
pp. 4781-4855 ◽  
Author(s):  
A. Stickler ◽  
H. Fischer ◽  
H. Bozem ◽  
C. Gurk ◽  
C. Schiller ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Atlantic Ocean ◽  
Dry Deposition ◽  
Trace Gases ◽  
Deposition Velocity ◽  
Organic Peroxides ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean ◽  
Positive Tendency

Abstract. We present a comparison of different Lagrangian and steady state box model runs with measurement data obtained during the GABRIEL campaign over the tropical Atlantic Ocean and the rainforest in the Guyanas, October 2005. Lagrangian modelling of boundary layer (BL) CO constrained by measurements of reactive trace gases and radiation is used to derive a horizontal gradient (≈5.6 pmol/mol km−1) of this compound from the ocean to the rainforest (east to west). This is significantly smaller than that derived from the measurements (16–48 pmol/mol km−1), indicating that photochemical production from organic precursors alone cannot explain the observed strong gradient. It appears that HCHO is overestimated by the Lagrangian and "steady state" models, which include dry deposition but not exchange with the free troposphere (FT). The relatively short lifetime of HCHO (50–100 min) implies substantial BL-FT exchange. The mixing-in of FT air affected by African and South American biomass burning at an estimated rate of 0.12 h−1 increases the CO and lowers the HCHO mixing ratios, leading to a better agreement with measurements. A 24 h mean deposition velocity of 1.35 cm/s for H2O2 over the ocean as well as over the rainforest is deduced assuming BL-FT exchange adequate to the results for CO. The measured increase of the organic peroxides from the ocean to the rainforest (≈0.66 nmol/mol d−1) is significantly overestimated by the Lagrangian model, even when using high values for the deposition velocity and the entrainment rate. Our results point at either heterogeneous loss of organic peroxides and/or their radical precursors or a missing reaction path of peroxy radicals not forming peroxides in isoprene chemistry. We calculate a mean integrated daytime net ozone production (NOP) in the BL of (0.2±5.9) nmol/mol (ocean) and (2.4±2.1) nmol/mol (rainforest). The NOP strongly correlates with NO and shows a positive tendency in the boundary layer over the rainforest.

scholarly journals A laboratory characterisation of inorganic iodine emissions from the sea surface: dependence on oceanic variables and parameterisation for global modelling

2013 ◽  
Vol 13 (12) ◽  
pp. 31445-31477 ◽  
Author(s):  
S. M. MacDonald ◽  
J. C. Gómez Martín ◽  
R. Chance ◽  
S. Warriner ◽  
A. Saiz-Lopez ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Environmental Parameters ◽  
Sea Surface ◽  
Total Iodine ◽  
Iodide Ions ◽  
Iodine Compounds ◽  
Halogen Chemistry ◽  
Inorganic Iodine

Abstract. Reactive iodine compounds play a~significant role in the atmospheric chemistry of the oceanic boundary layer by influencing the oxidising capacity through catalytically removing O3 and altering the HOx and NOx balance. The sea-to-air flux of iodine over the open ocean is therefore an important quantity in assessing these impacts on a global scale. This paper examines the effect of a number of relevant environmental parameters, including water temperature, salinity and organic compounds, on the magnitude of the HOI and I2 fluxes produced from the uptake of O3 and its reaction with iodide ions in aqueous solution. The results of these laboratory experiments and those reported previously (Carpenter et al., 2013), along with sea surface iodide concentrations measured or inferred from measurements of dissolved total iodine and iodate reported in the literature, were then used to produce parameterised expressions for the HOI and I2 fluxes as a function of wind speed, sea-surface temperature and O3. These expressions were used in the Tropospheric HAlogen chemistry MOdel (THAMO) to compare with MAX-DOAS measurements of iodine monoxide (IO) performed during the HaloCAST-P cruise in the Eastern Pacific ocean (Mahajan et al., 2012). The modelled IO agrees reasonably with the field observations, although significant discrepancies are found during a period of low wind speeds (<3 m s−1), when the model overpredicts IO by up to a factor of three. The inorganic iodine flux contributions to IO are found to be comparable to, or even greater than, the contribution of organo-iodine compounds and therefore its inclusion in atmospheric models is important to improve predictions of the influence of halogen chemistry in the marine boundary layer.

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