Year‐round measurements of nitrogen oxides and ozone in the tropical North Atlantic marine boundary layer

Lee, James; Møller, Sarah; Read, Katie A.; Lewis, Alastair C.; Mendes, Luis Miguel Domingues; Carpenter, Lucy J.

doi:10.1029/2009jd011878

Cited by 102 publications

(183 citation statements)

References 52 publications

(64 reference statements)

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“…This indicates that Cl accounted for 5.4−11.6% of total methane loss in the Cape Verde region, in accord with previous estimates. 9 The Cape Verde region is typically under ozone destruction conditions, due to the low levels of NO x : diurnal ozone loss was observed at CVAO 6,21 with average values of 3.3 ± 2.6 ppb/ day. The BASE cases could reproduce ozone destruction during the day, although the calculated destruction rates were higher than the observations by a factor of 2−3 (depending on the scenario: 6−14 ppb/day).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Sommariva

Glasow

2012

Environ. Sci. Technol.

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We used a one-dimensional model to simulate the chemical evolution of air masses in the tropical Atlantic Ocean, with a focus on halogen chemistry. The model results were compared to the observations of inorganic halogen species made in this region. The model could largely reproduce the measurements of most chlorine species, especially under unpolluted conditions, but overestimated sea salt chloride, BrCl, and bromine species. Agreement with the measurements could be improved by taking into account the reactivity with aldehydes and the effects of dimethyl sulfide (DMS) and Saharan dust on aerosol pH; a hypothetical HOX → X − aqueous-phase reaction could also improve the agreement with measured Cl 2 and HOCl, especially under semipolluted conditions. The results also showed that halogens speciation and concentrations are very sensitive to cloud processing. The model was used to calculate the impact of the observed levels of halogens: Cl atoms accounted for 5.4−11.6% of total methane sinks and halogens (mostly bromine and iodine) accounted for 35−40% of total ozone destruction. ■ INTRODUCTIONThe tropical marine boundary layer (MBL) is a region of particular interest for atmospheric chemistry: high levels of solar radiation, along with high temperatures and relative humidities, result in a highly oxidizing environment. It is estimated that the tropical atmosphere accounts for up to 80% of the global oxidation of methane (the second most important greenhouse gas) and that ∼25% of the global oxidation of methane occurs in the tropical MBL. 1 Halogen species (chlorine, bromine, iodine) are known to play an important role in the chemical processes of the MBL, particularly with regard to the nitrogen and ozone cycles, sulfur chemistry and particle formation: an overview of halogen chemistry and its impact on atmospheric chemical processes can be found in ref 2. Measurements of these species in the tropical region are sparse, but a number of recent studies 3−13 have reported observations of several halogen species in the tropical Atlantic Ocean. These studies suggested that halogen chemistry is responsible for a large fraction (∼30%) of ozone destruction in the Tropics 6 and up to 7% of the global methane destruction. 9 In this paper, we used the one-dimensional chemical model MISTRA to study halogen chemistry in the tropical Atlantic Ocean and the evolution of the chemical composition of air masses traveling across the ocean to the islands of Cape Verde, 900 km West of the coast of Africa. We compared the model results to the database of published observations of halogen species from this region with the objective of testing our understanding of halogen chemistry and of quantifying the impact of the observed halogens levels on ozone (O 3 ) and methane (CH 4 ). ■ METHODSModel. MISTRA is a one-dimensional model of the MBL. The model includes a description of meteorological and microphysical processes in the MBL and is described in detail in refs 14 and 15. Version 7.4.1 of MISTRA includes a number of improvement...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Sommariva

Glasow

2012

Environ. Sci. Technol.

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“…The observatory is in a region of high marine biological production and, for 95 % of the time, receives the prevailing northeasterly trade wind directly off the ocean (Read et al, 2008;. Measurements at the observatory are considered to be representative of the open ocean, and CO, O 3 , VOCs, NO x and NO y have been measured near-continuously at the observatory since October 2006 (Lee et al, 2009;.…”

Section: The Cape Verde Atmospheric Observatorymentioning

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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“…Calibration for NO 2 converter efficiency is by internal automatic gas-phase titration of NO with O 3 to form NO 2 with the NO signal measured with the BLC lamps active and inactive as described by Lee et al (2009). Artifacts in both NO and NO 2 are measured whilst sampling zero air.…”

Section: Instrumentationmentioning

confidence: 99%

“…Photolytic conversion has been demonstrated to be affected by a negative interference from the photolysis products of VOCs reacting with NO within the photolysis cell (Villena et al, 2012) and has a possible positive interference from thermal decomposition of NO y (McClenny et al, 2002). Measurements of NO and NO 2 have been made in a range of low-NO x locations using the chemiluminescence technique (Huntrieser et al, 2007;Lee et al, 2009;Peterson and Honrath, 1999;Zhang et al, 2008). Measurement of NO x by the NO chemiluminescent technique in these locations can be challenging (Yang et al, 2004), often operating close to the limit of detection (LOD).…”

Section: Introductionmentioning

confidence: 99%

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

et al. 2016

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Abstract. Measurement of NO 2 at low concentrations (tens of ppts) is non-trivial. A variety of techniques exist, with the conversion of NO 2 into NO followed by chemiluminescent detection of NO being prevalent. Historically this conversion has used a catalytic approach (molybdenum); however, this has been plagued with interferences. More recently, photolytic conversion based on UV-LED irradiation of a reaction cell has been used. Although this appears to be robust there have been a range of observations in low-NO x environments which have measured higher NO 2 concentrations than might be expected from steady-state analysis of simultaneously measured NO, O 3 , j NO 2 , etc. A range of explanations exist in the literature, most of which focus on an unknown and unmeasured "compound X" that is able to convert NO to NO 2 selectively. Here we explore in the laboratory the interference on the photolytic NO 2 measurements from the thermal decomposition of peroxyacetyl nitrate (PAN) within the photolysis cell. We find that approximately 5 % of the PAN decomposes within the instrument, providing a potentially significant interference. We parameterize the decomposition in terms of the temperature of the light source, the ambient temperature, and a mixing timescale (∼ 0.4 s for our instrument) and expand the parametric analysis to other atmospheric compounds that decompose readily to NO 2 (HO 2 NO 2 , N 2 O 5 , CH 3 O 2 NO 2 , IONO 2 , BrONO 2 , higher PANs). We apply these parameters to the output of a global atmospheric model (GEOS-Chem) to investigate the global impact of this interference on (1) the NO 2 measurements and (2) the NO 2 : NO ratio, i.e. the Leighton relationship. We find that there are significant interferences in cold regions with low NO x concentrations such as the Antarctic, the remote Southern Hemisphere, and the upper troposphere. Although this interference is likely instrument-specific, the thermal decomposition to NO 2 within the instrument's photolysis cell could give an at least partial explanation for the anomalously high NO 2 that has been reported in remote regions. The interference can be minimized by better instrument characterization, coupled to instrumental designs which reduce the heating within the cell, thus simplifying interpretation of data from remote locations.

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Year‐round measurements of nitrogen oxides and ozone in the tropical North Atlantic marine boundary layer

Cited by 102 publications

References 52 publications

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

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

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

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Year‐round measurements of nitrogen oxides and ozone in the tropical North Atlantic marine boundary layer

Cited by 102 publications

References 52 publications

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

Multiphase Halogen Chemistry in the Tropical Atlantic Ocean

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

Interferences in photolytic NO&lt;sub&gt;2&lt;/sub&gt; measurements: explanation for an apparent missing oxidant?

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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

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?