Iodine chemistry in the eastern Pacific marine boundary layer

Abstract The seasonal cycle of marine boundary layer (MBL) clouds over the eastern Pacific Ocean is studied with the International Pacific Research Center (IPRC) Regional Atmospheric Model (iRAM). The results show that the model is capable of simulating not only the overall seasonal cycle but also the spatial distribution, cloud regime transition, and vertical structure of MBL clouds over the eastern Pacific. Although the modeled MBL cloud layer is generally too high in altitude over the open ocean when compared with available satellite observations, the model simulated well the westward deepening and decoupling of the MBL, the rise in cloud base and cloud top of the low cloud decks off the Peru and California coasts, and the cloud regime transition from stratocumulus near the coast to trade cumulus farther to the west in both the southeast and northeast Pacific. In particular, the model reproduced major features of the seasonal variations in stratocumulus decks off the Peru and California coasts, including cloud amount, surface latent heat flux, subcloud-layer mixing, and the degree of MBL decoupling. In both observations and the model simulation, in the season with small low-level cloudiness, surface latent heat flux is large and the cloud base is high. This coincides with weak subcloud-layer mixing and strong entrainment at cloud top, characterized by a high degree of MBL decoupling, while the opposite is true for the season with large low-level cloudiness. This seasonal cycle in low-cloud properties resembles the downstream stratocumulus-to-cumulus transition of marine low clouds and can be explained by the “deepening–decoupling” mechanism proposed in previous studies. It is found that the seasonal variations of low-level clouds off the Peru coast are mainly caused by a large seasonal variability in sea surface temperature, whereas those off the California coast are largely attributed to the seasonal cycle in lower-tropospheric temperature.

Download Full-text

Modelling the impacts of iodine chemistry on the northern Indian Ocean marine boundary layer

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-8437-2021 ◽

2021 ◽

Vol 21 (11) ◽

pp. 8437-8454

Author(s):

Anoop S. Mahajan ◽

Qinyi Li ◽

Swaleha Inamdar ◽

Kirpa Ram ◽

Alba Badia ◽

...

Keyword(s):

Boundary Layer ◽

Chemical Composition ◽

Indian Ocean ◽

Marine Boundary Layer ◽

Indian Subcontinent ◽

Winter Period ◽

Monsoon Period ◽

Mean Values ◽

Iodine Chemistry ◽

Inorganic Iodine

Abstract. Recent observations have shown the ubiquitous presence of iodine oxide (IO) in the Indian Ocean marine boundary layer (MBL). In this study, we use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem version 3.7.1), including halogen (Br, Cl, and I) sources and chemistry, to quantify the impacts of the observed levels of iodine on the chemical composition of the MBL. The model results show that emissions of inorganic iodine species resulting from the deposition of ozone (O3) on the sea surface are needed to reproduce the observed levels of IO, although the current parameterizations overestimate the atmospheric concentrations. After reducing the inorganic emissions by 40 %, a reasonable match with cruise-based observations is found, with the model predicting values between 0.1 and 1.2 pptv across the model domain MBL. A strong seasonal variation is also observed, with lower iodine concentrations predicted during the monsoon period, when clean oceanic air advects towards the Indian subcontinent, and higher iodine concentrations predicted during the winter period, when polluted air from the Indian subcontinent increases the ozone concentrations in the remote MBL. The results show that significant changes are caused by the inclusion of iodine chemistry, with iodine-catalysed reactions leading to regional changes of up to 25 % in O3, 50 % in nitrogen oxides (NO and NO2), 15 % in hydroxyl radicals (OH), 25 % in hydroperoxyl radicals (HO2), and up to a 50 % change in the nitrate radical (NO3), with lower mean values across the domain. Most of the large relative changes are observed in the open-ocean MBL, although iodine chemistry also affects the chemical composition in the coastal environment and over the Indian subcontinent. These results show the importance of including iodine chemistry in modelling the atmosphere in this region.

Download Full-text

Marine Aerosol Iodine Chemistry: The Importance of Soluble Organic Iodine

Environmental Chemistry ◽

10.1071/en05070 ◽

2005 ◽

Vol 2 (4) ◽

pp. 295 ◽

Cited By ~ 65

Author(s):

Alex R. Baker

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Marine Aerosol ◽

Radiative Balance ◽

Iodine Species ◽

Ozone Destruction ◽

Organic Iodine ◽

Iodine Chemistry ◽

Inorganic Iodine ◽

Complex Chemistry

Environmental Context.Ozone concentrations play a large part in controlling the oxidation capacity of the marine boundary layer, while the production of new aerosol particles affects atmospheric radiative balance. Iodine has a complex chemistry in the marine atmosphere which impacts on both these processes. Much of this iodine chemistry, especially the chemical speciation of iodine in aerosol, is only poorly understood. This study explores the occurrence and abundance of organic forms of iodine, a topic that has received very little attention to date. Abstract.Iodine has a complex chemistry in aerosols in the marine boundary layer (MBL), and is involved in both ozone destruction and new aerosol particle formation processes. Work in this area has focussed almost exclusively on inorganic iodine chemistry. Results from two research cruises in the Atlantic Ocean, covering wide longitude (60°W to 0°W) and latitude (50°N to 50°S) ranges indicate that soluble organic iodine species are both widespread and abundant in marine aerosol. The reactivity of these species is yet to be determined, but may influence the concentrations of some aerosol inorganic iodine species, and may also impact on MBL ozone destruction reactions.

Download Full-text

Marine boundary layer structure as observed by A-train satellites

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-5891-2016 ◽

2016 ◽

Vol 16 (9) ◽

pp. 5891-5903 ◽

Cited By ~ 9

Author(s):

Tao Luo ◽

Zhien Wang ◽

Damao Zhang ◽

Bing Chen

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Layer Structure ◽

Mixing Layer ◽

Eastern Pacific ◽

Data Set ◽

Layer Height ◽

Boundary Layer Height ◽

Ocean Region ◽

Low Cloud

Abstract. The marine boundary layer (MBL) structure is important to the marine low cloud processes, and the exchange of heat, momentum, and moisture between oceans and the low atmosphere. This study examines the MBL structure over the eastern Pacific region and further explores the controlling factors of MBL structure over the global oceans with a new 4-year satellite-based data set. The MBL top (boundary layer height, BLH) and the mixing layer height (MLH) were identified using the MBL aerosol lidar backscattering from the CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations). Results showed that the MBL is generally decoupled with MLH ∕ BLH ratio ranging from ∼  0.5 to ∼  0.8 over the eastern Pacific Ocean region. The MBL decoupling magnitude is mainly controlled by estimated inversion strength (EIS), which in turn controls the cloud top entrainment process. The systematic differences between drizzling and non-drizzling stratocumulus tops also show dependence on EIS. This may be related to the meso-scale circulations or gravity wave in the MBL. Further analysis indicates that the MBL shows a similar decoupled structure for clear-sky and cumulus-cloud-topped conditions, but is better mixed under stratiform cloud breakup and overcast conditions.

Download Full-text

Mini ozone holes due to dust release of iodine

10.5194/egusphere-egu21-13841 ◽

2021 ◽

Author(s):

Rainer Volkamer ◽

Theodore Koenig ◽

Eric Apel ◽

James Bresch ◽

Carlos Cuevas ◽

...

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Oxidative Capacity ◽

Atmospheric Models ◽

Geological Time ◽

Iodine Monoxide ◽

Iodine Chemistry ◽

Dust Events ◽

Boundary Layer Ozone ◽

Odd Oxygen

Desert dust as a source of iron and other micronutrients is recognized to fertilize oceans, but little attention has been paid to dust as a source of iodine. Empirical observations find iodate on dust measured during ship cruises downwind of the Sahara desert. However, it remains unclear whether iodine in dust is the result of marine iodine uptake on dust during transport in the marine boundary layer, or whether such iodine accumulates over geological time scales, and is emitted together with dust. Significant enhancements of iodine have been observed in Sahara dust events in form of methyl iodide (CH3I) and iodine monoxide (IO) radicals, but atmospheric models currently do not consider dust as a source of iodine. Furthermore, dust plumes are often accompanied by significant ozone loss, which is commonly attributed to reactive uptake of O3 and other odd oxygen species (i.e., N2O5, HNO3) on dust surfaces. However, laboratory experiments struggle to reproduce the large reactive uptake coefficients needed to explain field observations, and do not consider iodine chemistry. We present evidence that dust induced "mini ozone holes" in the remote (Southern Hemisphere) lower free troposphere west of South America (TORERO field campaign) are largely the result of gas-phase iodine chemistry in otherwise unpolluted (low NOx) dust layers that originate from the Atacama and Sechura Deserts. Ozone concentrations inside these elevated dust layers are often 10-20 ppb, and as low as 3 ppb, and influence entrainment of low ozone air from aloft into the marine boundary layer. Ozone depletion is found to be widespread, extending up to 6km altitude, and thousands of kilometers along the coast. Elevated IO radical concentrations inside decoupled dust layers are higher than in the marine boundary layer, and serve as a source of iodine, and vigorous ozone sink following entrainment to the marine boundary layer. The implications for our perception of iodine sources, surface air quality, oxidative capacity, and climate are briefly discussed.

Download Full-text

Estimation of reactive inorganic iodine fluxes in the Indian and Southern Ocean marine boundary layer

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-12093-2020 ◽

2020 ◽

Vol 20 (20) ◽

pp. 12093-12114

Author(s):

Swaleha Inamdar ◽

Liselotte Tinel ◽

Rosie Chance ◽

Lucy J. Carpenter ◽

Prabhakaran Sabu ◽

...

Keyword(s):

Boundary Layer ◽

Southern Ocean ◽

Marine Boundary Layer ◽

Polar Front ◽

Sea Surface ◽

Optical Absorption Spectroscopy ◽

Surface Seawater ◽

Significance Level ◽

Iodine Species ◽

Iodine Chemistry

Abstract. Iodine chemistry has noteworthy impacts on the oxidising capacity of the marine boundary layer (MBL) through the depletion of ozone (O3) and changes to HOx (OH∕HO2) and NOx (NO∕NO2) ratios. Hitherto, studies have shown that the reaction of atmospheric O3 with surface seawater iodide (I−) contributes to the flux of iodine species into the MBL mainly as hypoiodous acid (HOI) and molecular iodine (I2). Here, we present the first concomitant observations of iodine oxide (IO), O3 in the gas phase, and sea surface iodide concentrations. The results from three field campaigns in the Indian Ocean and the Southern Ocean during 2015–2017 are used to compute reactive iodine fluxes in the MBL. Observations of atmospheric IO by multi-axis differential optical absorption spectroscopy (MAX-DOAS) show active iodine chemistry in this environment, with IO values up to 1 pptv (parts per trillion by volume) below latitudes of 40∘ S. In order to compute the sea-to-air iodine flux supporting this chemistry, we compare previously established global sea surface iodide parameterisations with new region-specific parameterisations based on the new iodide observations. This study shows that regional changes in salinity and sea surface temperature play a role in surface seawater iodide estimation. Sea–air fluxes of HOI and I2, calculated from the atmospheric ozone and seawater iodide concentrations (observed and predicted), failed to adequately explain the detected IO in this region. This discrepancy highlights the need to measure direct fluxes of inorganic and organic iodine species in the marine environment. Amongst other potential drivers of reactive iodine chemistry investigated, chlorophyll a showed a significant correlation with atmospheric IO (R=0.7 above the 99 % significance level) to the north of the polar front. This correlation might be indicative of a biogenic control on iodine sources in this region.

Download Full-text

Estimation of Reactive Inorganic Iodine Fluxes in the Indian and Southern Ocean Marine Boundary Layer

10.5194/acp-2019-1052 ◽

2020 ◽

Cited By ~ 1

Author(s):

Swaleha Inamdar ◽

Liselotte Tinel ◽

Rosie Chance ◽

Lucy J. Carpenter ◽

Prabhakaran Sabu ◽

...

Keyword(s):

Boundary Layer ◽

Southern Ocean ◽

Marine Boundary Layer ◽

Molecular Iodine ◽

Polar Front ◽

Sea Surface ◽

Surface Seawater ◽

Significance Level ◽

Iodine Species ◽

Iodine Chemistry

Abstract. Iodine chemistry has noteworthysignificant impacts on the oxidising capacity of the marine boundary layer (MBL) through the depletion of ozone (O3) and changes to HOx (OH/HO2) and NOx (NO/NO2) ratios. Hitherto, studies have shown that the reaction of atmospheric O3 with surface seawater iodide (I−) contributes to the flux of iodine species into the MBL mainly as hypoiodous acid (HOI) and molecular iodine (I2). Here, we present the first concomitant observations of iodine oxide (IO), O3 in the gas phase, and sea surface iodide concentrations. The results from three field campaigns in the Indian Ocean and the Southern Ocean during 2014–2017 are used to compute reactive iodine fluxes to the MBL. Observations of atmospheric IO by MAX-DOAS show active iodine chemistry in this environment, with IO values up to 1 pptv (parts per trillion by volume) below latitudes of 40° S. In order to compute the sea-to-air iodine flux supporting this chemistry, we compare previously established global sea surface iodide parameterisations with new, region-specific parameterisations based on the new iodide observations. This study shows that regional changes in salinity and sea surface temperature play a role in surface seawater iodide estimation. Sea-air fluxes of HOI and I2, calculated from the atmospheric ozone and seawater iodide concentrations (observed and predicted), failed to adequately explain the detected IO in this region. This discrepancy highlights the need to measure direct fluxes of inorganic and organic iodine species in the marine environment. Amongst other potential drivers of reactive iodine chemistry investigated, chlorophyll-a showed a significant correlation with atmospheric IO (R = 0.7 above the 99 % significance level) to the north of the polar front. This correlation might be indicative of a biogenic control on iodine sources in this region.

Download Full-text