scholarly journals Measurements and modelling of molecular iodine emissions, transport and photodestruction in the coastal region around Roscoff

2010 ◽  
Vol 10 (23) ◽  
pp. 11823-11838 ◽  
Author(s):  
R. J. Leigh ◽  
S. M. Ball ◽  
J. Whitehead ◽  
C. Leblanc ◽  
A. J. L. Shillings ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Coastal Region ◽  
Molecular Iodine ◽  
Transport Processes ◽  
Optical Absorption Spectroscopy ◽  
Emission Rates ◽  
Cavity Ringdown Spectroscopy ◽  
The Relationship

Abstract. Iodine emissions from the dominant six macroalgal species in the coastal regions around Roscoff, France, have been modelled to support the Reactive Halogens in the Marine Boundary Layer Experiment (RHaMBLe) undertaken in September 2006. A two-dimensional model is used to explore the relationship between geographically resolved regional emissions (based on maps of seaweed beds in the area and seaweed I2 emission rates previously measured in the laboratory) and in situ point and line measurements of I2 performed respectively by a broadband cavity ringdown spectroscopy (BBCRDS) instrument sited on the shoreline and a long-path differential optical absorption spectroscopy (LP-DOAS) instrument sampling over an extended light path to an off-shore island. The modelled point and line I2 concentrations compare quantitatively with BBCRDS and LP-DOAS measurements, and provide a link between emission fields and the different measurement geometries used to quantify atmospheric I2 concentrations during RHaMBLe. Total I2 emissions over the 100 km2 region around Roscoff are calculated to be 1.7×1019 molecules per second during the lowest tides. During the night, the model replicates I2 concentrations up to 50 pptv measured along the LP-DOAS instrument's line of sight, and predicts spikes of several hundred pptv in certain conditions. Point I2 concentrations up to 50 pptv are also calculated at the measurement site, in broad agreement with the BBCRDS observations. Daytime measured concentrations of I2 at the site correlate with modelled production and transport processes. However substantial recycling of the photodissociated I2 is required for the model to quantitatively match measured concentrations. This result corroborates previous modelling of iodine and NOx chemistry in the semi-polluted marine boundary layer which proposed a mechanism for recycling I2 via the formation, transport and subsequent reactions of the IONO2 reservoir compound. The methodology presented in this paper provides a tool for linking spatially distinct measurements to inhomogeneous and temporally varying emission fields.

scholarly journals Measurements and modelling of molecular iodine emissions, transport and photodestruction in the coastal region around Roscoff

2009 ◽  
Vol 9 (5) ◽  
pp. 21165-21198 ◽  
Author(s):  
R. J. Leigh ◽  
S. M. Ball ◽  
J. Whitehead ◽  
C. Leblanc ◽  
A. J. L. Shillings ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Coastal Region ◽  
Molecular Iodine ◽  
Transport Processes ◽  
Local Source ◽  
Emission Rates ◽  
Regional Emissions ◽  
Absolute Concentrations ◽  
The Relationship ◽  
D Model

Abstract. Emissions from the dominant six macroalgal species in the coastal regions around Rosccoff, France, have been modelled to support the Reactive Halogens in the Marine Boundary Layer Experiment (RHaMBLE) campaign undertaken in September 2006. A 2-D model was used to explore the relationship between point and line measurements of molecular iodine concentrations, and total regional emissions, based on seaweed I2 emission rates measured in the laboratory. The relatively simple modelling technique has produced modelled point and line data, which compare quantitatively with campaign measurements, and provide a link between emission fields and the different measurement geometries used to quantify atmospheric I2 concentrations during RHaMBLE. During nightime, absolute concentrations in the region of 5 pptv are predicted and measured in the LP-DOAS measurements, with site concentrations predicted and measured up to 40 pptv, compatible with concentrations above Laminariales beds of approximately 2.5 ppbv. Daytime measured concentrations of I2 at site correlate with modelled production and transport processes, however complete recycling of photodissociated I2 is required in the model to quantitatively match measured concentrations. Additional local source terms are suggested to provide a feasible mechanism to account for this discrepancy.Total of I2 emissions over the 100 km2 region around Roscoff are calculated as 1.5×1019 molecules per second during the lowest tides.

scholarly journals In situ measurements of molecular iodine in the marine boundary layer: the link to macroalgae and the implications for O<sub>3</sub>, IO, OIO and NO<sub>x</sub>

2010 ◽  
Vol 10 (1) ◽  
pp. 361-390
Author(s):  
R.-J. Huang ◽  
K. Seitz ◽  
J. Buxmann ◽  
D. Poehler ◽  
K. E. Hornsby ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Single Point ◽  
Molecular Iodine ◽  
In Situ Measurements ◽  
Gas Chromatography Mass Spectrometry ◽  
Optical Absorption Spectroscopy ◽  
Mixing Ratios ◽  
Concentration Levels

Abstract. "Single-point" in situ measurements of molecular iodine (I2) were carried out in the coastal marine boundary layer (MBL) using diffusion denuders in combination with a gas chromatography-mass spectrometry (GC-MS) method. Comparison measurements were taken at Mace Head and Mweenish Bay, on the West Coast of Ireland. The observed mixing ratios of I2 at Mweenish Bay are much higher than that at Mace Head, indicating the emissions of I2 are correlated with the local algal biomass density and algae species. The concentration levels of I2 were found to correlate inversely with tidal height and correlate positively with the concentration levels of O3 in the surrounding air. However, the released I2 can also lead to O3 destruction via the reaction of O3 with iodine atoms that are formed by the photolysis of I2 during the day and via the reaction of I2 with NOx at night. IO and OIO were measured by long-path differential optical absorption spectroscopy (LP-DOAS). The results show that the concentrations of both daytime and nighttime IO are correlated with the mixing ratios of I2. OIO was observed not only during the day but also, for the first time at both Mace Head and Mweenish Bay, at night. In addition, I2 was measured simultaneously by the LP-DOAS technique and compared with the "single-point" in situ measurement. The results suggest that the local algae sources dominate the inorganic iodine chemistry at Mace Head and Mweenish Bay.

scholarly journals In situ measurements of molecular iodine in the marine boundary layer: the link to macroalgae and the implications for O<sub>3</sub>, IO, OIO and NO<sub>x</sub>

2010 ◽  
Vol 10 (10) ◽  
pp. 4823-4833 ◽  
Author(s):  
R.-J. Huang ◽  
K. Seitz ◽  
J. Buxmann ◽  
D. Pöhler ◽  
K. E. Hornsby ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Algal Species ◽  
Molecular Iodine ◽  
In Situ Measurements ◽  
Gas Chromatography Mass Spectrometry ◽  
Optical Absorption Spectroscopy ◽  
Atmospheric Measurements ◽  
Mixing Ratios ◽  
Inorganic Iodine

Abstract. Discrete in situ atmospheric measurements of molecular iodine (I2) were carried out at Mace Head and Mweenish Bay on the west coast of Ireland using diffusion denuders in combination with a gas chromatography-mass spectrometry (GC-MS) method. I2, IO and OIO were also measured by long-path differential optical absorption spectroscopy (LP-DOAS). The simultaneous denuder and LP-DOAS I2 measurements were well correlated (R2=0.80) but the denuder method recorded much higher concentrations. This can be attributed to the fact that the in situ measurements were made near to macroalgal sources of I2 in the intertidal zone, whereas the LP-DOAS technique provides distance-averaged mixing ratios of an inhomogeneous distribution along the light-path. The observed mixing ratios of I2 at Mweenish Bay were significantly higher than that at Mace Head, which is consistent with differences in local algal biomass density and algal species composition. Above algal beds, levels of I2 were found to correlate inversely with tidal height and positively with the concentrations of O3 in the surrounding air, indicating a role for O3 in the production of I2 from macroalgae, as has been previously suggested from laboratory studies. However, measurements made ~150 m away from the algal beds showed a negative correlation between O3 and I2 during both day and night. We interpret these results to indicate that the released I2 can also lead to O3 destruction via the reaction of O3 with I atoms that are formed by the photolysis of I2 during the day and via the reaction of I2 with NO3 radicals at night. The results show that the concentrations of daytime IO are correlated with the mixing ratios of I2, and suggest that the local algae sources dominate the inorganic iodine chemistry at Mace Head and Mweenish Bay.

scholarly journals Modelling molecular iodine emissions in a coastal marine environment: the link to new particle formation

2006 ◽  
Vol 6 (4) ◽  
pp. 883-895 ◽  
Author(s):  
A. Saiz-Lopez ◽  
J. M. C. Plane ◽  
G. McFiggans ◽  
P. I. Williams ◽  
S. M. Ball ◽  
...  
Keyword(s):  
Inductively Coupled Plasma ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Molecular Iodine ◽  
Nano Particles ◽  
Optical Absorption Spectroscopy ◽  
Iodine Chemistry ◽  
The Impact ◽  
New Particles

Abstract. A model of iodine chemistry in the marine boundary layer (MBL) has been used to investigate the impact of daytime coastal emissions of molecular iodine (I2). The model contains a full treatment of gas-phase iodine chemistry, combined with a description of the nucleation and growth, by condensation and coagulation, of iodine oxide nano-particles. In-situ measurements of coastal emissions of I2 made by the broadband cavity ring-down spectroscopy (BBCRDS) and inductively coupled plasma-mass spectrometry (ICP/MS) techniques are presented and compared to long path differential optical absorption spectroscopy (DOAS) observations of I2 at Mace Head, Ireland. Simultaneous measurements of enhanced I2 emissions and particle bursts show that I2 is almost certainly the main precursor of new particles at this coastal location. The ratio of IO to I2 predicted by the model indicates that the iodine species observed by the DOAS are concentrated over a short distance (about 8% of the 4.2 km light path) consistent with the intertidal zone, bringing them into good agreement with the I2 measurements made by the two in-situ techniques. The model is then used to investigate the effect of iodine emission on ozone depletion, and the production of new particles and their evolution to form stable cloud condensation nuclei (CCN).

scholarly journals Modelling molecular iodine emissions in a coastal marine environment: the link to new particle formation

2005 ◽  
Vol 5 (4) ◽  
pp. 5405-5439 ◽  
Author(s):  
A. Saiz-Lopez ◽  
J. M. C. Plane ◽  
G. McFiggans ◽  
P. I. Williams ◽  
S. M. Ball ◽  
...  
Keyword(s):  
Inductively Coupled Plasma ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Molecular Iodine ◽  
Nano Particles ◽  
Optical Absorption Spectroscopy ◽  
Iodine Chemistry ◽  
The Impact ◽  
New Particles

Abstract. A model of iodine chemistry in the marine boundary layer (MBL) has been used to investigate the impact of daytime coastal emissions of molecular iodine (I2). The model contains a full treatment of gas-phase iodine chemistry, combined with a description of the nucleation and growth, by condensation and coagulation, of iodine oxide nano-particles. In-situ measurements of coastal emissions of I2 made by the broadband cavity ring-down spectroscopy (BBCRDS) and inductively coupled plasma-mass spectrometry (ICP/MS) techniques are presented and compared to long path differential optical absorption spectroscopy (DOAS) observations of I2 at Mace Head, Ireland. Simultaneous measurements of enhanced I2 emissions and particle bursts show that I2 is almost certainly the main precursor of new particles at this coastal location. The ratio of IO to I2 predicted by the model indicates that the iodine species observed by the DOAS are concentrated over a short distance (about 8% of the 4.2 km light path) consistent with the intertidal zone, bringing them into good agreement with the I2 measurements made by the two in-situ techniques. The model is then used to investigate the effect of iodine emission on ozone depletion, and the production of new particles and their evolution to form stable cloud condensation nuclei (CCN).

scholarly journals A broadband cavity ringdown spectrometer for in-situ measurements of atmospheric trace gases

2005 ◽  
Vol 5 (3) ◽  
pp. 3491-3532 ◽  
Author(s):  
M. Bitter ◽  
S. M. Ball ◽  
I. M. Povey ◽  
R. L. Jones
Keyword(s):  
Boundary Layer ◽  
Water Vapour ◽  
Marine Boundary Layer ◽  
Thermal Dissociation ◽  
Optical Absorption Spectroscopy ◽  
Integration Time ◽  
Research Station ◽  
Absorption Bands ◽  
Optical Extinction ◽  
Cavity Ringdown

Abstract. This paper describes a broadband cavity ringdown spectrometer and its deployment during the 2002 North Atlantic Marine Boundary Layer Experiment (NAMBLEX) to measure ambient concentrations of NO3, N2O5, I2 and OIO at the Mace Head Atmospheric Research Station, Co. Galway, Ireland. The effective absorption path lengths accessible with the spectrometer generally exceeded 10 km, enabling sensitive localised ''point'' measurements of atmospheric absorbers to be made adjacent to the other instruments monitoring chemically related species at the same site. For the majority of observations, the spectrometer was used in an open path configuration thereby avoiding surface losses of reactive species. A subset of observations targeted the N2O5 molecule by detecting the additional NO3 formed by the thermal dissociation of N2O5. In all cases the concentrations of the atmospheric absorbers were retrieved by fitting the differential structure in the broadband cavity ringdown spectra using a methodology adapted from long path differential optical absorption spectroscopy. The uncertainty of the retrieval depends crucially on the correct treatment and fitting of the absorption bands due to water vapour, a topic that is discussed in the context of analysing broadband cavity ringdown spectra. The quality of the measurements and the retrieval method are illustrated with representative spectra acquired during NAMBLEX in spectral regions around 660 nm (NO3 and N2O5) and 570 nm (I2 and OIO). Typical detection limits were 1 pptv for NO3 in an integration time of 100 s, 4 pptv for OIO and 20 pptv for I2 in an integration time of 10 min. Additionally, the concentrations of atmospheric water vapour and the aerosol optical extinction were retrieved in both spectral regions. A companion paper in this issue presents the time series of the measurements and discusses their significance for understanding the variability of short lived nitrogen and iodine compounds in the marine boundary layer.

scholarly journals Tracer measurements in the tropical tropopause layer during the AMMA/SCOUT-O3 aircraft campaign

2010 ◽  
Vol 10 (8) ◽  
pp. 3615-3627 ◽  
Author(s):  
C. D. Homan ◽  
C. M. Volk ◽  
A. C. Kuhn ◽  
A. Werner ◽  
J. Baehr ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Transport Processes ◽  
Gradual Transition ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Multidisciplinary Analysis ◽  
The Tropics

Abstract. We present airborne in situ measurements made during the AMMA (African Monsoon Multidisciplinary Analysis)/SCOUT-O3 campaign between 31 July and 17 August 2006 on board the M55 Geophysica aircraft, based in Ouagadougou, Burkina Faso. CO2 and N2O were measured with the High Altitude Gas Analyzer (HAGAR), CO was measured with the Cryogenically Operated Laser Diode (COLD) instrument, and O3 with the Fast Ozone ANalyzer (FOZAN). We analyse the data obtained during five local flights to study the dominant transport processes controlling the tropical tropopause layer (TTL, here ~350–375 K) and lower stratosphere above West-Africa: deep convection up to the level of main convective outflow, overshooting of deep convection, and horizontal inmixing across the subtropical tropopause. Besides, we examine the morphology of the stratospheric subtropical barrier. Except for the flight of 13 August, distinct minima in CO2 mixing ratios indicate convective outflow of boundary layer air in the TTL. The CO2 profiles show that the level of main convective outflow was mostly located at potential temperatures between 350 and 360 K, and for 11 August reached up to 370 K. While the CO2 minima indicate quite significant convective influence, the O3 profiles suggest that the observed convective signatures were mostly not fresh, but of older origin (several days or more). When compared with the mean O3 profile measured during a previous campaign over Darwin in November 2005, the O3 minimum at the main convective outflow level was less pronounced over Ouagadougou. Furthermore O3 mixing ratios were much higher throughout the whole TTL and, unlike over Darwin, rarely showed low values observed in the regional boundary layer. Signatures of irreversible mixing following overshooting of convective air were scarce in the tracer data. Some small signatures indicative of this process were found in CO2 profiles between 390 and 410 K during the flights of 4 and 8 August, and in CO data at 410 K on 7 August. However, the absence of expected corresponding signatures in other tracer data makes this evidence inconclusive, and overall there is little indication from the observations that overshooting convection has a profound impact on gas-phase tracer TTL composition during AMMA. We find the amount of photochemically aged air isentropically mixed into the TTL across the subtropical tropopause to be not significant. Using the N2O observations we estimate the fraction of aged extratropical stratospheric air in the TTL to be 0.0±0.1 up to 370 K during the local flights. Above the TTL this fraction increases to 0.3±0.1 at 390 K. The subtropical barrier, as indicated by the slope of the correlation between N2O and O3 between 415 and 490 K, does not appear as a sharp border between the tropics and extratropics, but rather as a gradual transition region between 10° N and 25° N where isentropic mixing between these two regions may occur.

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.

scholarly journals Evaluation of stratocumulus cloud prediction in the Met Office forecast model during VOCALS-REx

2010 ◽  
Vol 10 (21) ◽  
pp. 10541-10559 ◽  
Author(s):  
S. J. Abel ◽  
D. N. Walters ◽  
G. Allen
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Coastal Region ◽  
Forecast Model ◽  
Good Representation ◽  
Liquid Water Path ◽  
Water Path

Abstract. Observations in the subtropical southeast Pacific obtained during the VOCALS-REx field experiment are used to evaluate the representation of stratocumulus cloud in the Met Office forecast model and to identify key areas where model biases exist. Marked variations in the large scale structure of the cloud field were observed during the experiment on both day-to-day and on diurnal timescales. In the remote maritime region the model is shown to have a good representation of synoptically induced variability in both cloud cover and marine boundary layer depth. Satellite observations show a strong diurnal cycle in cloud fraction and liquid water path in the stratocumulus with enhanced clearances of the cloud deck along the Chilean and Peruvian coasts on certain days. The model accurately simulates the phase of the diurnal cycle but is unable to capture the coastal clearing of cloud. Observations along the 20° S latitude line show a gradual increase in the depth of the boundary layer away from the coast. This trend is well captured by the model (typical low bias of 200 m) although significant errors exist at the coast where the model marine boundary layer is too shallow and moist. Drizzle in the model responds to changes in liquid water path in a manner that is consistent with previous ship-borne observations in the region although the intensity of this drizzle is likely to be too high, particularly in the more polluted coastal region where higher cloud droplet number concentrations are typical. Another mode of variability in the cloud field that the model is unable to capture are regions of pockets of open cellular convection embedded in the overcast stratocumulus deck and an example of such a feature that was sampled during VOCALS-REx is shown.

scholarly journals Iodine-mediated coastal particle formation: an overview of the Reactive Halogens in the Marine Boundary Layer (RHaMBLe) Roscoff coastal study

2010 ◽  
Vol 10 (6) ◽  
pp. 2975-2999 ◽  
Author(s):  
G. McFiggans ◽  
C. S. E. Bale ◽  
S. M. Ball ◽  
J. M. Beames ◽  
W. J. Bloss ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ultrafine Particles ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Measurement Techniques ◽  
Ultrafine Particle ◽  
Molecular Iodine ◽  
Particle Formation ◽  
North West ◽  
Iodine Species

Abstract. This paper presents a summary of the measurements made during the heavily-instrumented Reactive Halogens in the Marine Boundary Layer (RHaMBLe) coastal study in Roscoff on the North West coast of France throughout September 2006. It was clearly demonstrated that iodine-mediated coastal particle formation occurs, driven by daytime low tide emission of molecular iodine, I2, by macroalgal species fully or partially exposed by the receding waterline. Ultrafine particle concentrations strongly correlate with the rapidly recycled reactive iodine species, IO, produced at high concentrations following photolysis of I2. The heterogeneous macroalgal I2 sources lead to variable relative concentrations of iodine species observed by path-integrated and in situ measurement techniques. Apparent particle emission fluxes were associated with an enhanced apparent depositional flux of ozone, consistent with both a direct O3 deposition to macroalgae and involvement of O3 in iodine photochemistry and subsequent particle formation below the measurement height. The magnitude of the particle formation events was observed to be greatest at the lowest tides with the highest concentrations of ultrafine particles growing to the largest sizes, probably by the condensation of anthropogenically-formed condensable material. At such sizes the particles should be able to act as cloud condensation nuclei at reasonable atmospheric supersaturations.

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