Concurrent observations of atomic iodine, molecular iodine and ultrafine particles in a coastal environment

Mahajan, Anoop S.; Sorribas, M.; Martı́n, Juan Carlos Gómez; MacDonald, S. M.; Gil, Manuel; Plane, J. M. C.; Saiz‐Lopez, Alfonso

doi:10.5194/acpd-10-27227-2010

Cited by 10 publications

(9 citation statements)

References 37 publications

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“…Particles were counted using an ultrafine concentration particle counter (UCPC) (TSI‐Model 3776) (see Mahajan et al . [] for a detailed description of this setup). A scan‐up time of 270 s and a time resolution of 300 s allowed measurements of a size range between 9 and 438 nm (diameter).…”

Section: Methodsmentioning

confidence: 99%

“…This debate can be traced back to the seminal modeling work published in 1980 by Chameides and Davis [] and has recently gained momentum following the suggestion of a significant regional impact of halogens on O 3 , NO x , and HO x in the tropical Atlantic MBL [ Read et al ., ]. Additional impetus has been provided by the proposed participation of iodine in secondary aerosol formation, suggested by frequently observed iodine‐driven coastal particle bursts [ O'Dowd et al ., ; Whitehead et al ., ; Mahajan et al ., ].…”

Section: Introductionmentioning

confidence: 98%

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Iodine chemistry in the eastern Pacific marine boundary layer

et al. 2013

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[1] Observations of gas-phase iodine species were made during a field campaign in the eastern Pacific marine boundary layer (MBL). The Climate and Halogen Reactivity Tropical Experiment (CHARLEX) in the Galápagos Islands, running from September 2010 to present, is the first long-term ground-based study of trace gases in this region. Observations of gas-phase iodine species were made using long-path differential optical absorption spectroscopy (LP-DOAS), multi-axis DOAS (MAX-DOAS), and resonance and off-resonance fluorescence by lamp excitation (ROFLEX). These measurements were supported by ancillary measurements of ozone, nitrogen oxides, and meteorological variables. Selective halocarbon and ultrafine aerosol concentration measurements were also made. MAX-DOAS observations of iodine monoxide (IO) display a weak seasonal variation. The maximum differential slant column density was 3.8 Â 10 13 molecule cm À2 (detection limit~7 Â 10 12 molecule cm À2 ). The seasonal variation of reactive iodine IO x (= I + IO) is stronger, peaking at 1.6 pptv during the warm season (February-April). This suggests a dependence of the iodine sources on the annual cycle in sea surface temperature, although perturbations by changes in ocean surface iodide concentration and solar radiation are also possible. An observed negative correlation of IO x with chlorophyll-a indicates a predominance of abiotic sources. The low IO mixing ratios measured (below the LP-DOAS detection limit of 0.9 pptv) are not consistent with satellite observations if IO is confined to the MBL. The IO x loading is consistent with the observed absence of strong ozone depletion and nucleation events, indicating a small impact of iodine chemistry on these climatically relevant factors in the eastern Pacific MBL.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Iodine chemistry in the eastern Pacific marine boundary layer

et al. 2013

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“…Since the level of uncertainty is even larger than for the I x O y , it has not been included in the mechanism. Saiz-Lopez et al, 2006;Huang et al, 2010;Mahajan et al, 2011;Atkinson et al, 2012).…”

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confidence: 99%

Iodine chemistry in the troposphere and its effect on ozone

et al. 2014

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Abstract. Despite the potential influence of iodine chemistry on the oxidizing capacity of the troposphere, reactive iodine distributions and their impact on tropospheric ozone remain almost unexplored aspects of the global atmosphere. Here we present a comprehensive global modelling experiment aimed at estimating lower and upper limits of the inorganic iodine burden and its impact on tropospheric ozone. Two sets of simulations without and with the photolysis of I x O y oxides (i.e. I 2 O 2 , I 2 O 3 and I 2 O 4 ) were conducted to define the range of inorganic iodine loading, partitioning and impact in the troposphere. Our results show that the most abundant daytime iodine species throughout the middle to upper troposphere is atomic iodine, with an annual average tropical abundance of (0.15-0.55) pptv. We propose the existence of a "tropical ring of atomic iodine" that peaks in the tropical upper troposphere (∼11-14 km) at the equator and extends to the sub-tropics (30 • N-30 • S). Annual average daytime I / IO ratios larger than 3 are modelled within the tropics, reaching ratios up to ∼20 during vigorous uplift events within strong convective regions. We calculate that the integrated contribution of catalytic iodine reactions to the total rate of tropospheric ozone loss (IO x Loss ) is 2-5 times larger than the combined bromine and chlorine cycles. When I x O y photolysis is included, IO x Loss represents an upper limit of approximately 27, 14 and 27 % of the tropical annual ozone loss for the marine boundary layer (MBL), free troposphere (FT) and upper troposphere (UT), respectively, while the lower limit throughout the tropical troposphere is ∼9 %. Our results indicate that iodine is the second strongest ozone-depleting family throughout the global marine UT and in the tropical MBL.We suggest that (i) iodine sources and its chemistry need to be included in global tropospheric chemistry models, (ii) experimental programs designed to quantify the iodine budget in the troposphere should include a strategy for the measurement of atomic I, and (iii) laboratory programs are needed to characterize the photochemistry of higher iodine oxides to determine their atmospheric fate since they can potentially dominate halogen-catalysed ozone destruction in the troposphere.

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“…3542 D. Stone et al: Impacts of bromine and iodine chemistry on tropospheric OH and HO 2 Figgans et al, 2004Figgans et al, , 2010Mahajan et al, 2011;Sherwen et al, 2016c).…”

Section: Introductionmentioning

confidence: 99%

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

et al. 2018

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Abstract. The chemistry of the halogen species bromine and iodine has a range of impacts on tropospheric composition, and can affect oxidising capacity in a number of ways. However, recent studies disagree on the overall sign of the impacts of halogens on the oxidising capacity of the troposphere. We present simulations of OH and HO 2 radicals for comparison with observations made in the remote tropical ocean boundary layer during the Seasonal Oxidant Study at the Cape Verde Atmospheric Observatory in 2009. We use both a constrained box model, using detailed chemistry derived from the Master Chemical Mechanism (v3.2), and the three-dimensional global chemistry transport model GEOSChem. Both model approaches reproduce the diurnal trends in OH and HO 2 . Absolute observed concentrations are well reproduced by the box model but are overpredicted by the global model, potentially owing to incomplete consideration of oceanic sourced radical sinks. The two models, however, differ in the impacts of halogen chemistry. In the box model, halogen chemistry acts to increase OH concentrations (by 9.8 % at midday at the Cape Verde Atmospheric Observatory), while the global model exhibits a small increase in OH at the Cape Verde Atmospheric Observatory (by 0.6 % at midday) but overall shows a decrease in the global annual mass-weighted mean OH of 4.5 %. These differences reflect the variety of timescales through which the halogens impact the chemical system. On short timescales, photolysis of HOBr and HOI, produced by reactions of HO 2 with BrO and IO, respectively, increases the OH concentration. On longer timescales, halogen-catalysed ozone destruction cycles lead to lower primary production of OH radicals through ozone photolysis, and thus to lower OH concentrations. The global model includes more of the longer timescale responses than the constrained box model, and overall the global impact of the longer timescale response (reduced primary production due to lower O 3 concentrations) overwhelms the shorter timescale response (enhanced cycling from HO 2 to OH), and thus the global OH concentration decreases. The Earth system contains many such responses on a large range of timescales. This work highlights the care that needs to be taken to understand the full impact of any one process on the system as a whole.

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Concurrent observations of atomic iodine, molecular iodine and ultrafine particles in a coastal environment

Cited by 10 publications

References 37 publications

Iodine chemistry in the eastern Pacific marine boundary layer

Iodine chemistry in the eastern Pacific marine boundary layer

Iodine chemistry in the troposphere and its effect on ozone

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

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Concurrent observations of atomic iodine, molecular iodine and ultrafine particles in a coastal environment

Cited by 10 publications

References 37 publications

Iodine chemistry in the eastern Pacific marine boundary layer

Iodine chemistry in the eastern Pacific marine boundary layer

Iodine chemistry in the troposphere and its effect on ozone

Impacts of bromine and iodine chemistry on tropospheric OH and HO&lt;sub&gt;2&lt;/sub&gt;: comparing observations with box and global model perspectives

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Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives