Evidence for Substantial Variations of Atmospheric Hydroxyl Radicals in the Past Two Decades

Prinn, Ronald G.; Huang, J.; Weiss, Ray F.; Cunnold, D. M.; Fraser, Paul J.; Simmonds, Peter; McCulloch, Archie; Harth, Christina M.; Salameh, Peter K.; O’Doherty, Simon; Wang, R. H. J.; Porter, L. W.; Miller, B. R.

doi:10.1126/science.1058673

Cited by 592 publications

(615 citation statements)

References 26 publications

Supporting

Mentioning

559

Contrasting

Unclassified

Order By: Relevance

“…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)(9)(10)(11).…”

mentioning

confidence: 82%

The importance of weak absorption features in promoting tropospheric radical production

Matthews

Sinha

Francisco

2005

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

View full text Add to dashboard Cite

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...

show abstract

mentioning

confidence: 82%

The importance of weak absorption features in promoting tropospheric radical production

Matthews

Sinha

Francisco

2005

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

View full text Add to dashboard Cite

show abstract

“…Montzka et al (2011) inferred small interannual OH variability and trends (typical OH changes from year to year of less than 3 %) and attributed previously estimated large year-to-year OH variations before 1998 (e.g. Bousquet et al, 2005;Prinn et al, 2001) to overly large sensitivity of OH concentrations inferred from methyl chloroform measurements to uncertainties in the latter's emissions. However, Prinn et al (2005) also showed lower post-1998 OH variability that they attributed to the lack of strong post-1998 El Niño events.…”

Section: Oh Oxidationmentioning

confidence: 99%

The global methane budget 2000–2012

Saunois

Bousquet

Poulter

et al. 2016

Earth Syst. Sci. Data

948

733

View full text Add to dashboard Cite

Abstract. The global methane (CH 4 ) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH 4 over the past decade. Emissions and concentrations of CH 4 are continuing to increase, making CH 4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH 4 sources that overlap geographically, and from the destruction of CH 4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (∼ biennial) updates of the global methane budget. This consortium includes atmospheric physicists and chemists, biogeochemists of surface and marine emissions, and socio-economists who study anthropogenic emissions. Following Kirschke et al. (2013), we propose here the first version of a living review paper that integrates results of top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories and data-driven approaches (including process-based models for estimating land surface emissions and atmospheric chemistry, and inventories for anthropogenic emissions, data-driven extrapolations). . Top-down inversions consistently infer lower emissions in China (∼ 58 Tg CH 4 yr −1 , range 51-72, −14 %) and higher emissions in Africa (86 Tg CH 4 yr −1 , range 73-108, +19 %) than bottom-up values used as prior estimates. Overall, uncertainties for anthropogenic emissions appear smaller than those from natural sources, and the uncertainties on source categories appear larger for top-down inversions than for bottom-up inventories and models.The most important source of uncertainty on the methane budget is attributable to emissions from wetland and other inland waters. We show that the wetland extent could contribute 30-40 % on the estimated range for wetland emissions. Other priorities for improving the methane budget include the following: (i) the development of process-based models for inland-water emissions, (ii) the intensification of methane observations at local scale (flux measurements) to constrain bottom-up land surface models, and at regional scale (surface networks and satellites) to constrain top-down inversions, (iii) improvements in the estimation of atmospheric loss by OH, and (iv) improvements of the transport models integrated in top-down inversions.

show abstract

“…[123][124][125][126][127] Long-term changes in global OH concentrations, and therefore in the atmospheric residence times of many gases, are a matter of great interest but remain highly uncertain. 128,129 Recent field campaigns have studied pollutants in the remote troposphere, 130 -133 the outflow from East Asia, 134 -143 the Indian subcontinent, 143 and North America. 144 -148 Several regional-scale studies have been carried out in the United States 149 -153 and Europe 154 -157 that demonstrated the enormous pollutant potential of major cites and "megalopolis" regions, as well as the fact that significant quantities of gaseous pollutants and fine particles can be transported and detected over intercontinental scales.…”

Section: Global Pollutant Transportmentioning

confidence: 99%

Megacities and Atmospheric Pollution

Molina

2004

Journal of the Air & Waste Management Association

692

372

View full text Add to dashboard Cite

About half of the world's population now lives in urban areas because of the opportunity for a better quality of life. Many of these urban centers are expanding rapidly, leading to the growth of megacities, which are defined as metropolitan areas with populations exceeding 10 million inhabitants. These concentrations of people and activity are exerting increasing stress on the natural environment, with impacts at urban, regional and global levels. In recent decades, air pollution has become one of the most important problems of megacities. Initially, the main air pollutants of concern were sulfur compounds, which were generated mostly by burning coal. Today, photochemical smog-induced primarily from traffic, but also from industrial activities, power generation, and solvents-has become the main source of concern for air quality, while sulfur is still a major problem in many cities of the developing world. Air pollution has serious impacts on public health, causes urban and regional haze, and has the potential to contribute significantly to climate change. Yet, with appropriate planning, megacities can efficiently address their air quality problems through measures such as application of new emission control technologies and development of mass transit systems.This review is focused on nine urban centers, chosen as case studies to assess air quality from distinct perspectives: from cities in the industrialized nations to cities in the developing world. While each city-its problems, resources, and outlook-is unique, the need for a holistic approach to the complex environmental problems is the same. There is no single strategy in reducing air pollution in megacities; a mix of policy measures will be needed to improve air quality. Experience shows that strong political will coupled with public dialog is essential to effectively implement the regulations required to address air quality problems.

show abstract

Evidence for Substantial Variations of Atmospheric Hydroxyl Radicals in the Past Two Decades

Cited by 592 publications

References 26 publications

The importance of weak absorption features in promoting tropospheric radical production

The importance of weak absorption features in promoting tropospheric radical production

The global methane budget 2000–2012

Megacities and Atmospheric Pollution

Contact Info

Product

Resources

About