The chemistry of OH and HO&lt;sub&gt;2&lt;/sub&gt; radicals in the boundary layer over the tropical Atlantic Ocean

Abstract. Fluorescence Assay by Gas Expansion (FAGE) has been used to detect ambient levels of OH and HO2 radicals at the Cape Verde Atmospheric Observatory, located in the tropical Atlantic marine boundary layer, during May and June 2007. Midday radical concentrations were high, with maximum concentrations of 9×106 molecule cm−3 and 6×108 molecule cm−3 observed for OH and HO2, respectively. A box model incorporating the detailed Master Chemical Mechanism, extended to include halogen chemistry, and constrained by all available measurements including halogen and nitrogen oxides, has been used to assess the chemical and physical parameters controlling the radical chemistry. IO and BrO, although present only at a few pptv, constituted ~23% of the instantaneous sinks for HO2. Modelled HO2 was sensitive to both HCHO concentration and the rate of heterogeneous loss to the ocean surface and aerosols. However, a unique combination of these parameters could not be found that gave optimised (to within 15%) agreement during both the day and night. The results imply a missing nighttime source of HO2. The model underpredicted the daytime (sunrise to sunset) OH concentration by 12%. Photolysis of HOI and HOBr accounted for ~13% of the instantaneous rate of OH formation. Taking into account that halogen oxides increase the oxidation of NOx (NO→NO2), and in turn reduce the rate of formation of OH from the reaction of HO2 with NO, OH concentrations were estimated to be 10% higher overall due to the presence of halogens. The increase in modelled OH from halogen chemistry gives an estimated 10% shorter lifetime for methane in this region, and the inclusion of halogen chemistry is necessary to model the observed daily cycle of ozone destruction that is observed at the surface. Due to surface losses, we hypothesise that HO2 concentrations increase with height and therefore contribute a larger fraction of the ozone destruction than at the surface.

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The chemistry of OH and HO<sub>2</sub> radicals in the boundary layer over the tropical Atlantic Ocean

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-1555-2010 ◽

2010 ◽

Vol 10 (4) ◽

pp. 1555-1576 ◽

Cited By ~ 110

Author(s):

L. K. Whalley ◽

K. L. Furneaux ◽

A. Goddard ◽

J. D. Lee ◽

A. Mahajan ◽

...

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Chemical Mechanism ◽

Sensitivity Analyses ◽

Physical Parameters ◽

Tropical Atlantic ◽

Halogen Chemistry ◽

Gas Expansion ◽

Halogen Oxides

Abstract. Fluorescence Assay by Gas Expansion (FAGE) has been used to detect ambient levels of OH and HO2 radicals at the Cape Verde Atmospheric Observatory, located in the tropical Atlantic marine boundary layer, during May and June 2007. Midday radical concentrations were high, with maximum concentrations of 9 ×106 molecule cm−3 and 6×108 molecule cm−3 observed for OH and HO2, respectively. A box model incorporating the detailed Master Chemical Mechanism, extended to include halogen chemistry, heterogeneous loss processes and constrained by all available measurements including halogen and nitrogen oxides, has been used to assess the chemical and physical parameters controlling the radical chemistry. The model was able to reproduce the daytime radical concentrations to within the 1 σ measurement uncertainty of 20% during the latter half of the measurement period but significantly under-predicted [HO2] by 39% during the first half of the project. Sensitivity analyses demonstrate that elevated [HCHO] (~2 ppbv) on specific days during the early part of the project, which were much greater than the mean [HCHO] (328 pptv) used to constrain the model, could account for a large portion of the discrepancy between modelled and measured [HO2] at this time. IO and BrO, although present only at a few pptv, constituted ~19% of the instantaneous sinks for HO2, whilst aerosol uptake and surface deposition to the ocean accounted for a further 23% of the HO2 loss at noon. Photolysis of HOI and HOBr accounted for ~13% of the instantaneous OH formation. Taking into account that halogen oxides increase the oxidation of NOx (NO → NO2), and in turn reduce the rate of formation of OH from the reaction of HO2 with NO, OH concentrations were estimated to be 9% higher overall due to the presence of halogens. The increase in modelled OH from halogen chemistry gives an estimated 9% shorter lifetime for methane in this region, and the inclusion of halogen chemistry is necessary to model the observed daily cycle of O3 destruction that is observed at the surface. Due to surface losses, we hypothesise that HO2 concentrations increase with height and therefore contribute a larger fraction of the O3 destruction than at the surface.

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Radicals in the marine boundary layer during NEAQS 2004: a model study of day-time and night-time sources and sinks

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-3075-2009 ◽

2009 ◽

Vol 9 (9) ◽

pp. 3075-3093 ◽

Cited By ~ 24

Author(s):

R. Sommariva ◽

H. D. Osthoff ◽

S. S. Brown ◽

T. S. Bates ◽

T. Baynard ◽

...

Keyword(s):

Boundary Layer ◽

New England ◽

Gas Phase ◽

Marine Boundary Layer ◽

Peroxy Radical ◽

Chemical Mechanism ◽

Physical Parameters ◽

Peroxy Radicals ◽

Night Time ◽

Aerosol Composition

Abstract. This paper describes a modelling study of several HOx and NOx species (OH, HO2, organic peroxy radicals, NO3 and N2O5) in the marine boundary layer. A model based upon the Master Chemical Mechanism (MCM) was constrained to observations of chemical and physical parameters made onboard the NOAA ship R/V Brown as part of the New England Air Quality Study (NEAQS) in the summer of 2004. The model was used to calculate [OH] and to determine the composition of the peroxy radical pool. Modelled [NO3] and [N2O5] were compared to in-situ measurements by Cavity Ring-Down Spectroscopy. The comparison showed that the model generally overestimated the measurements by 30–50%, on average. The model results were analyzed with respect to several chemical and physical parameters, including uptake of NO3 and N2O5 on fog droplets and on aerosol, dry deposition of NO3 and N2O5, gas-phase hydrolysis of N2O5 and reactions of NO3 with NMHCs and peroxy radicals. The results suggest that fog, when present, is an important sink for N2O5 via rapid heterogeneous uptake. The comparison between the model and the measurements were consistent with values of the heterogeneous uptake coefficient of N2O5 (γN2O5)>1×10−2, independent of aerosol composition in this marine environment. The analysis of the different loss processes of the nitrate radical showed the important role of the organic peroxy radicals, which accounted for a significant fraction (median: 15%) of NO3 gas-phase removal, particularly in the presence of high concentrations of dimethyl sulphide (DMS).

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A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

Atmospheric Chemistry and Physics ◽

10.5194/acp-4-1961-2004 ◽

2004 ◽

Vol 4 (7) ◽

pp. 1961-1987 ◽

Cited By ~ 30

Author(s):

K. Toyota ◽

Y. Kanaya ◽

M. Takahashi ◽

H. Akimoto

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Box Model ◽

Chemical Mechanism ◽

Oh Radicals ◽

Halogen Chemistry ◽

Reactive Halogen Species ◽

Oceanic Emissions ◽

Chemical Scheme ◽

Halogen Species

Abstract. A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit description of oxidative degradation of up to C3-hydrocarbons (CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in forming halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from a reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. The reaction between Br atoms and C2H2 is shown to be unimportant for determining the degree of bromine activation in the remote MBL. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

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A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-3-4549-2003 ◽

2003 ◽

Vol 3 (5) ◽

pp. 4549-4632 ◽

Cited By ~ 1

Author(s):

K. Toyota ◽

Y. Kanaya ◽

M. Takahashi ◽

H. Akimoto

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Box Model ◽

Chemical Mechanism ◽

Oh Radicals ◽

Halogen Chemistry ◽

Reactive Halogen Species ◽

Oceanic Emissions ◽

Chemical Scheme ◽

Halogen Species

Abstract. A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit treatment of oxidative degradation of up to C3-hydrocarbons CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in the formation of halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. On the other hand, the reaction between Br atoms and C2H2 is unimportant for determining the degree of bromine activation in the remote MBL. It is suggested that peroxyacetic acid formed via CH3CHO oxidation is one of the important chemical agents for triggering autocatalytic halogen release from sea-salt aerosols. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

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Radicals in the marine boundary layer during NEAQS 2004: a model study of day-time and night-time sources and sinks

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-16643-2008 ◽

2008 ◽

Vol 8 (4) ◽

pp. 16643-16692 ◽

Cited By ~ 5

Author(s):

R. Sommariva ◽

H. D. Osthoff ◽

S. S. Brown ◽

T. S. Bates ◽

T. Baynard ◽

...

Keyword(s):

Boundary Layer ◽

New England ◽

Gas Phase ◽

Marine Boundary Layer ◽

Peroxy Radical ◽

Chemical Mechanism ◽

Physical Parameters ◽

Peroxy Radicals ◽

Night Time ◽

Aerosol Composition

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Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-2193-2006 ◽

2006 ◽

Vol 6 (8) ◽

pp. 2193-2214 ◽

Cited By ~ 59

Author(s):

Z. L. Fleming ◽

P. S. Monks ◽

A. R. Rickard ◽

D. E. Heard ◽

W. J. Bloss ◽

...

Keyword(s):

Boundary Layer ◽

Production Rate ◽

Marine Boundary Layer ◽

Strong Dependence ◽

Peroxy Radical ◽

Chemical Mechanism ◽

Ozone Production ◽

Peroxy Radicals ◽

Night Time ◽

Model Measurement

Abstract. Peroxy radical (HO2+ΣRO2) measurements, using the PEroxy Radical Chemical Amplification (PERCA) technique at the North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) at Mace Head in summer 2002, are presented and put into the context of marine, boundary-layer chemistry. A suite of other chemical parameters (NO, NO2, NO3, CO, CH4, O3, VOCs, peroxides), photolysis frequencies and meteorological measurements, are used to present a detailed analysis of the role of peroxy radicals in tropospheric oxidation cycles and ozone formation. Under the range of conditions encountered the peroxy radical daily maxima varied from 10 to 40 pptv. The diurnal cycles showed an asymmetric shape typically shifted to the afternoon. Using a box model based on the master chemical mechanism the average model measurement agreement was 2.5 across the campaign. The addition of halogen oxides to the model increases the level of model/measurement agreement, apparently by respeciation of HOx. A good correlation exists between j(HCHO).[HCHO] and the peroxy radicals indicative of the importance of HCHO in the remote atmosphere as a HOx source, particularly in the afternoon. The peroxy radicals showed a strong dependence on [NO2] with a break point at 0.1 ppbv, where the radicals increased concomitantly with the reactive VOC loading, this is a lower value than seen at representative urban campaigns. The HO2/(HO2+ΣRO2) ratios are dependent on [NOx] ranging between 0.2 and 0.6, with the ratio increasing linearly with NOx. Significant night-time levels of peroxy radicals were measured up to 25 pptv. The contribution of ozone-alkenes and NO3-alkene chemistry to night-time peroxy radical production was shown to be on average 59 and 41%. The campaign mean net ozone production rate was 0.11±0.3 ppbv h-1. The ozone production rate was strongly dependent on [NO] having linear sensitivity (dln(P(O3))/dln(NO)=1.0). The results imply that the N(O3) (the in-situ net photochemical rate of ozone production/destruction) will be strongly sensitive in the marine boundary layer to small changes in [NO] which has ramifications for changing NOx loadings in the European continental boundary layer.

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

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-31445-2013 ◽

2013 ◽

Vol 13 (12) ◽

pp. 31445-31477 ◽

Cited By ~ 1

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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Sunrise ozone destruction found in the sub-tropical marine boundary layer

Geophysical Research Letters ◽

10.1029/1999gl010836 ◽

1999 ◽

Vol 26 (22) ◽

pp. 3377-3380 ◽

Cited By ~ 50

Author(s):

Ippei Nagao ◽

Kiyoshi Matsumoto ◽

Hiroshi Tanaka

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Ozone Destruction

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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.

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Investigation of processes controlling summertime gaseous elemental mercury oxidation at midlatitudinal marine, coastal, and inland sites

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-8461-2016 ◽

2016 ◽

Vol 16 (13) ◽

pp. 8461-8478 ◽

Cited By ~ 16

Author(s):

Zhuyun Ye ◽

Huiting Mao ◽

Che-Jen Lin ◽

Su Youn Kim

Keyword(s):

Marine Boundary Layer ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Box Model ◽

Chemical Mechanism ◽

Gaseous Elemental Mercury ◽

Diurnal Cycles ◽

Mixing Ratios ◽

Halogen Chemistry ◽

Marine Site

Abstract. A box model incorporating a state-of-the-art chemical mechanism for atmospheric mercury (Hg) cycling was developed to investigate the oxidation of gaseous elemental mercury (GEM) at three locations in the northeastern United States: Appledore Island (AI; marine), Thompson Farm (TF; coastal, rural), and Pack Monadnock (PM; inland, rural, elevated). The chemical mechanism in this box model included the most up-to-date Hg and halogen chemistry. As a result, the box model was able to simulate reasonably the observed diurnal cycles of gaseous oxidized mercury (GOM) and chemical speciation bearing distinct differences between the three sites. In agreement with observations, simulated GOM diurnal cycles at AI and TF showed significant daytime peaks in the afternoon and nighttime minimums compared to flat GOM diurnal cycles at PM. Moreover, significant differences in the magnitude of GOM diurnal amplitude (AI > TF > PM) were captured in modeled results. At the coastal and inland sites, GEM oxidation was predominated by O3 and OH, contributing 80–99 % of total GOM production during daytime. H2O2-initiated GEM oxidation was significant (∼ 33 % of the total GOM) at the inland site during nighttime. In the marine boundary layer (MBL) atmosphere, Br and BrO became dominant GEM oxidants, with mixing ratios reaching 0.1 and 1 pptv, respectively, and contributing ∼ 70 % of the total GOM production during midday, while O3 dominated GEM oxidation (50–90 % of GOM production) over the remaining day when Br and BrO mixing ratios were diminished. The majority of HgBr produced from GEM+Br was oxidized by NO2 and HO2 to form brominated GOM species. Relative humidity and products of the CH3O2+BrO reaction possibly significantly affected the mixing ratios of Br or BrO radicals and subsequently GOM formation. Gas–particle partitioning could potentially be important in the production of GOM as well as Br and BrO at the marine site.

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