Photochemistry of HO<sub><i>x</i></sub> in the upper troposphere at northern midlatitudes

Jaeglé, Lyatt; Jacob, Daniel J.; Brune, William H.; Faloona, I. C.; Tan, David; Heikes, Brian G.; Kondo, Yasuyuki; Sachse, G. W.; Anderson, B. E.; Gregory, G. L.; Singh, H. B.; Pueschel, R. F.; Ferry, G. V.; Blake, D. R.; Shetter, R. E.

doi:10.1029/1999jd901016

Cited by 189 publications

(242 citation statements)

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“…Studies by Krol et al (6) show a significant global increase in OH, whereas those by Prinn et al (7) show a decline in OH levels after 1988. Recent studies in the upper troposphere also have reported discrepancies between model predictions and measured HO x (where HO X ϵ OH ϩ HO 2 ) concentrations that strongly depend on solar zenith angles (8)(9)(10)(11). These differences between predictions and observation not only highlight the difficulties associated with measuring atmospheric OH concentrations, but also potential variability arising from incomplete accounting of all significant sources and sinks of the OH radical.…”

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confidence: 93%

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The importance of weak absorption features in promoting tropospheric radical production

Matthews

Sinha

Francisco

2005

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

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Atmospheric field measurement and modeling studies have long noted discrepancies between observation and predictions of OH and HO 2 concentrations in the atmosphere. Novel photochemical mechanisms have been proposed to explain these differences. Although inclusion of these additional sources improves agreement, they are unable to fully account for the observations. We report and demonstrate the importance of weak electronic absorption features, normally ignored or not measured, in contributing to significant OH radical production. Experiments on methyl hydroperoxide, a prototypical organic peroxide in large abundance in the troposphere, highlights how photochemistry in the neglected electronic absorption tail makes an important addition to the tropospheric OH budget. The present results underscore the need to measure absorption cross sections for atmospheric molecules over a wider dynamic range, especially over the wavelength regions where the solar flux is high, to fully quantitate their contributions to atmospheric photochemistry.absorption cross section ͉ atmospheric photochemistry ͉ electronic absorption ͉ methyl hydroperoxide ͉ photodissociation M ost gases emitted into the atmosphere by natural and anthropogenic activities are removed by their reaction with OH radicals (1-5). Indeed, OH radicals are often called the ''detergent'' of the atmosphere as reaction of trace gases with hydroxyl radicals leads to the oxidation of these volatile compounds and their ultimate removal from the atmosphere (1). Even though it exists in relatively small concentrations, Ϸ10 6 ͞ cm 3 , without the presence of OH radicals the composition of the atmosphere would be vastly different and potentially hazardous as the absence of this radical would lead to a large build-up of toxic atmospheric gases, many of which can also contribute to the greenhouse effect. Hence, accurate modeling of the oxidizing or cleansing capacity of the atmosphere requires knowledge of all significant sources of the hydroxyl radicals. Although several studies have suggested large changes in OH abundances in the atmosphere over the past decades, the direction of the change is apparently unclear. Studies by Krol et al. (6) show a significant global increase in OH, whereas those by Prinn et al. (7) show a decline in OH levels after 1988. Recent studies in the upper troposphere also have reported discrepancies between model predictions and measured HO x (where HO X ϵ OH ϩ HO 2 ) concentrations that strongly depend on solar zenith angles (8-11). These differences between predictions and observation not only highlight the difficulties associated with measuring atmospheric OH concentrations, but also potential variability arising from incomplete accounting of all significant sources and sinks of the OH radical. In this article we present experimental evidence that demonstrates that absorption from oftenneglected weak tails of electronic absorption bands can lead to significant amounts of photochemically generated OH radicals that, apparently, are currently una...

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confidence: 93%

“…The near-UV photodissociation of CH 3 OOH is known to be a significant source of OH radicals (10), whereas the reaction CH 3 OOH ϩ OH is an important removal mechanism for OH in the upper troposphere (14). Current tropospheric models include only the photochemistry associated with UV photodissociation of CH 3 OOH between 210 and 360 nm (26).…”

mentioning

confidence: 99%

The importance of weak absorption features in promoting tropospheric radical production

Matthews

Sinha

Francisco

2005

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

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“…HCOOH measurements in the upper troposphere, performed during several aircraft campaigns (Reiner et al, 1999;Jaeglé et al, 2000;Singh et al, 2000), have reported mixing ratios from about 30 to 215 pptv. HCOOH has also been probed in different biomass burning plumes (Yokelson et al, 1999;Goode et al, 2000;Herndon et al, 2007) with concentrations of around ten ppbv; Worden et al (1997) reported HCOOH total columns of 8.6 and 11.2 × 10 16 molec cm −2 above two fire events in the USA using optical measurements in the infrared.…”

Section: Formic Acidmentioning

confidence: 99%

Global distributions of methanol and formic acid retrieved for the first time from the IASI/MetOp thermal infrared sounder

et al. 2011

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Abstract. Methanol (CH 3 OH) and formic acid (HCOOH) are among the most abundant volatile organic compounds present in the atmosphere. In this work, we derive the global distributions of these two organic species using for the first time the Infrared Atmospheric Sounding Interferometer (IASI) launched onboard the MetOp-A satellite in 2006. This paper describes the method used and provides a first critical analysis of the retrieved products. The retrieval process follows a two-step approach in which global distributions are first obtained on the basis of a simple radiance indexing (transformed into brightness temperatures), and then mapped onto column abundances using suitable conversion factors. For methanol, the factors were calculated using a complete retrieval approach in selected regions. In the case of formic acid, a different approach, which uses a set of forward simulations for representative atmospheres, has been used. In both cases, the main error sources are carefully determined: the average relative error on the column for both species is estimated to be about 50%, increasing to about 100% for the least favorable conditions. The distributions for the year 2009 are discussed in terms of seasonality and source identification. Time series comparing methanol, formic acid and carbon monoxide in different regions are also presented.

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“…As a result, measurements of CH 2 O provide a valuable check of photochemical model predictions concerning recent hydrocarbon oxidation [Liu et al, 1992;Lee et al, 1998;Fried et al, 2002Fried et al, , 2003aWert et al, 2003]. In addition, CH 2 O measurements are important to the calculation of accurate OH concentration fields and odd hydrogen (HO x ) budgets [Ayers et al, 1997;Fried et al, 1997a;Wennberg et al, 1998;Jaeglé et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

Design and performance of a tunable diode laser absorption spectrometer for airborne formaldehyde measurements

Wert

2003

J. Geophys. Res.

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[1] A tunable diode laser absorption spectrometer (TDLAS) was modified for highprecision and high-time-resolution formaldehyde (CH 2 O) measurements. This enhanced system was deployed in both the clean and polluted troposphere, as part of aircraft missions (TOPSE 2000, TexAQS 2000, and TRACE-P 2001 and ground-based missions (SOS 1999). Measurements of very constant ambient CH 2 O concentrations were used to determine instrument precisions, which were stable under normal operating conditions, with the exception of brief aircraft cabin pressure changes. Precisions of 15-50 pptv (1s) were typically achieved for 1 min of averaging, corresponding to absorptions of 0.5-1.7 Â 10 À6 , 3-5 times better than the previous version of the instrument (1998

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Photochemistry of HO_x in the upper troposphere at northern midlatitudes

Cited by 189 publications

References 52 publications

The importance of weak absorption features in promoting tropospheric radical production

The importance of weak absorption features in promoting tropospheric radical production

Global distributions of methanol and formic acid retrieved for the first time from the IASI/MetOp thermal infrared sounder

Design and performance of a tunable diode laser absorption spectrometer for airborne formaldehyde measurements

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Photochemistry of HOx in the upper troposphere at northern midlatitudes

Cited by 189 publications

References 52 publications

The importance of weak absorption features in promoting tropospheric radical production

The importance of weak absorption features in promoting tropospheric radical production

Global distributions of methanol and formic acid retrieved for the first time from the IASI/MetOp thermal infrared sounder

Design and performance of a tunable diode laser absorption spectrometer for airborne formaldehyde measurements

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Photochemistry of HO_x in the upper troposphere at northern midlatitudes