Assessment of upper tropospheric HO<sub>x</sub> sources over the tropical Pacific based on NASA GTE/PEM data: Net effect on HO<sub>x</sub> and other photochemical parameters

Crawford, J. H.; Davis, Douglas D.; Olson, J. R.; Chen, G.; Liu, S.; Gregory, G. L.; Barrick, J. D.; Sachse, G. W.; Sandholm, S. T.; Heikes, Brian G.; Singh, H. B.; Blake, D. R.

doi:10.1029/1999jd900106

Cited by 129 publications

(148 citation statements)

References 51 publications

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“…The model conceptually follows the work by Crawford et al (44), and the chemical mechanism includes both gas-phase and heterogeneous reactions of iodine and bromine species based on works by Ordóñez et al …”

Section: Methodsmentioning

confidence: 99%

Detection of iodine monoxide in the tropical free troposphere

Dix

Baidar

Bresch

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

118

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Atmospheric iodine monoxide (IO) is a radical that catalytically destroys heat trapping ozone and reacts further to form aerosols. Here, we report the detection of IO in the tropical free troposphere (FT). We present vertical profiles from airborne measurements over the Pacific Ocean that show significant IO up to 9.5 km altitude and locate, on average, two-thirds of the total column above the marine boundary layer. IO was observed in both recent deep convective outflow and aged free tropospheric air, suggesting a widespread abundance in the FT over tropical oceans. Our vertical profile measurements imply that most of the IO signal detected by satellites over tropical oceans could originate in the FT, which has implications for our understanding of iodine sources. Surprisingly, the IO concentration remains elevated in a transition layer that is decoupled from the ocean surface. This elevated concentration aloft is difficult to reconcile with our current understanding of iodine lifetimes and may indicate heterogeneous recycling of iodine from aerosols back to the gas phase. Chemical model simulations reveal that the iodine-induced ozone loss occurs mostly above the marine boundary layer (34%), in the transition layer (40%) and FT (26%) and accounts for up to 20% of the overall tropospheric ozone loss rate in the upper FT. Our results suggest that the halogen-driven ozone loss in the FT is currently underestimated. More research is needed to quantify the widespread impact that iodine species of marine origin have on free tropospheric composition, chemistry, and climate.atmospheric chemistry | oxidative capacity | halogens | heterogeneous chemistry | air-sea exchange R eactive iodine impacts atmospheric chemistry in several ways. Catalytic reaction cycles involving iodine atoms and iodine monoxide (IO; I x = I + IO) destroy tropospheric ozone, which is a primary source for OH radicals (1, 2). Halogens contribute ∼45% of the ozone loss in the remote tropical marine boundary layer (MBL) (2-4). IO further affects the oxidative capacity of the atmosphere through fast reactions with HO 2 radicals and the resulting changes in HO x (HO x = OH + HO 2 ) (1, 2). Iodine also affects NO x (NO x = NO + NO 2 ) by oxidizing NO to NO 2 (1-4). Additionally, bromine atom recycling by IO increases ozone destruction and mercury oxidation rates in the MBL, resulting in higher mercury deposition rates to ecosystems and increased availability to the food chain (2, 5, 6). Finally, in coastal regions, the formation of ultrafine aerosol particles from iodine oxides can be a source of cloud condensation nuclei that can modify Earth's albedo and thus, the radiative budget of the atmosphere (2, 7).Oceans are the main source of iodine to the atmosphere. Most current knowledge of iodine sources and chemistry is based on measurements in the MBL (3,(8)(9)(10)(11)(12)(13). IO observations at coastal MBL sites primarily link iodine sources to macroalgae (8-10). More recent studies have measured IO at open ocean sites (3, 11-13), suggesting that ther...

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Section: Methodsmentioning

confidence: 99%

Detection of iodine monoxide in the tropical free troposphere

Dix

Baidar

Bresch

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

118

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“…The 2cs detection limit for the NO system used in this study was estimated at 6 pptv. After the field deployment, the instrument's calibration was further evaluated using an NO calibration system developed at Georgia The photochemical box model used in this study was similar to that described previously by our group [Crawford et al, 1999]. This model assumes all calculated species to be in steady state, and includes 250 reactions.…”

Section: Measurement Techniques and Model Descriptionmentioning

confidence: 99%

Unexpected high levels of NO observed at South Pole

Davis¹,

Nowak²,

Chen³

et al. 2001

Geophysical Research Letters

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202

195

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Abstract. Reported here are the first Austral summer measurements of NO at South Pole (SP). They are unique in that the levels are one to two orders of magnitude higher (i.e., median, 225 pptv) than measured at other polar sites. The available evidence suggests that these elevated levels are the result of photodenitrification of the snowpack, in conjunction with a very thin atmospheric mixing depth. Important chemical consequences included finding the atmospheric oxidizing power at SP to be an order of magnitude higher than expected. Measurement Techniques and Model DescriptionNO was measured using a modified chemiluminescence instrument. The instrument was operated in a 50% duty cycle mode, switching between measurements and zero every 5 minutes. Two standard addition calibrations and zero air (artifact) tests were performed each day. The NO calibration gas was intercompared with other NIST traceable standards both before and after the field deployment and was found to be within the manufacturers tolerance (+2 %). The 2cs detection limit for the NO system used in this study was estimated at 6 pptv. After the field deployment, the instrument's calibration was further evaluated using an NO calibration system developed at Georgia

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“…Reactions and rates for basic HO x -NO x -CH 4 -CO chemistry are those recommended by Sander et al (2006) and Atkinson et al (2006). Non-methane hydrocarbon (NMHC) chemistry is originally based on the lumped scheme from Lurmann et al (1986), with adjustments as discussed in the appendix of Crawford et al (1999). Because halogen chemistry is expected to impact surface O 3 chemistry and radical cycling near the surface and in the lower troposphere the box model is updated to include bromine photochemistry (see Table 1).…”

Section: Box Modelmentioning

confidence: 99%

An analysis of fast photochemistry over high northern latitudes during spring and summer using in-situ observations from ARCTAS and TOPSE

Olson

Brune

Mao³

et al. 2012

Atmos. Chem. Phys.

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Abstract.Observations of chemical constituents and meteorological quantities obtained during the two Arctic phases of the airborne campaign ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) are analyzed using an observationally constrained steady state box model. Measurements of OH and HO 2 from the Penn State ATHOS instrument are compared to model predictions. Forty percent of OH measurements below 2 km are at the limit of detection during the spring phase (ARCTAS-A). While the median observed-to-calculated ratio is near one, both the scatter of observations and the model uncertainty for OH are at the magnitude of ambient values. During the summer phase (ARCTAS-B), model predictions of OH are biased low relative to observations and demonstrate a high sensitivity to the level of uncertainty in NO observations. Predictions of HO 2 using observed CH 2 O and H 2 O 2 as model constraints are up to a factor of two larger than observed. A temperature-dependent terminal loss rate of HO 2 to aerosol recently proposed in the literature is shown to be insufficient to reconcile these differences. A comparison of ARCTAS-A to the high latitude springtime portion of the 2000 TOPSE campaign (Tropospheric Ozone Production about the Spring Equinox) shows similar meteorological and chemical environments with the exception of peroxides; observations of H 2 O 2 during ARCTAS-A were 2.5 to 3 times larger than those during TOPSE. The cause of this difference in peroxides remains unresolved and has important implications for the Arctic HO x budget. Unconstrained model predictions for both phases indicate photochemistry alone is unable to simultaneously sustain observed levels of CH 2 O and H 2 O 2 ; however when the model is constrained with observed CH 2 O, H 2 O 2 predictions from a range of Published by Copernicus Publications on behalf of the European Geosciences Union. J. R. Olson et al.: An analysis of fast photochemistry over high northern latitudesrainout parameterizations bracket its observations. A mechanism suitable to explain observed concentrations of CH 2 O is uncertain. Free tropospheric observations of acetaldehyde (CH 3 CHO) are 2-3 times larger than its predictions, though constraint of the model to those observations is sufficient to account for less than half of the deficit in predicted CH 2 O. The box model calculates gross O 3 formation during spring to maximize from 1-4 km at 0.8 ppbv d −1 , in agreement with estimates from TOPSE, and a gross production of 2-4 ppbv d −1 in the boundary layer and upper troposphere during summer. Use of the lower observed levels of HO 2 in place of model predictions decreases the gross production by 25-50 %. Net O 3 production is near zero throughout the ARCTAS-A troposphere, and is 1-2 ppbv in the boundary layer and upper altitudes during ARCTAS-B.

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Assessment of upper tropospheric HO_x sources over the tropical Pacific based on NASA GTE/PEM data: Net effect on HO_x and other photochemical parameters

Cited by 129 publications

References 51 publications

Detection of iodine monoxide in the tropical free troposphere

Detection of iodine monoxide in the tropical free troposphere

Unexpected high levels of NO observed at South Pole

An analysis of fast photochemistry over high northern latitudes during spring and summer using in-situ observations from ARCTAS and TOPSE

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Assessment of upper tropospheric HOx sources over the tropical Pacific based on NASA GTE/PEM data: Net effect on HOx and other photochemical parameters

Cited by 129 publications

References 51 publications

Detection of iodine monoxide in the tropical free troposphere

Detection of iodine monoxide in the tropical free troposphere

Unexpected high levels of NO observed at South Pole

An analysis of fast photochemistry over high northern latitudes during spring and summer using in-situ observations from ARCTAS and TOPSE

Contact Info

Product

Resources

About

Assessment of upper tropospheric HO_x sources over the tropical Pacific based on NASA GTE/PEM data: Net effect on HO_x and other photochemical parameters