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9 results on '"tropospheric oh"'

1. Trifluoroacetic acid from degradation of HCFCs and HFCs: A three-dimensional modeling study

Author

Kotamarthi, V. R, Rodriguez, J. M, Ko, M. K. W, Tromp, T. K, Sze, N. D, and Prather, Michael J

Subjects
atmospheric chemistry, hydrofluorocarbon 134a, tropospheric oh, hfc-134a, parameterization, radicals, cf3cfho, water, fate
Abstract

Trifluoroacetic acid (TFA; CF3 COOH) is produced by the degradation of the halocarbon replacements HFC-134a, HCFC-124, and HCFC-123. The formation of TFA occurs by HFC/HCFC reacting with OH to yield CF3COX (X = F or Cl), followed by in-cloud hydrolysis of CF3COX to form TFA. The TFA formed in the clouds may be reevaporated but is finally deposited onto the surface by washout or dry deposition. Concern has been expressed about the possible long-term accumulation of TFA in certain aquatic environments, pointing to the need to obtain information on the concentrations of TFA in rainwater over scales ranging from local to continental. Based on projected concentrations for HFC-134a, HCFC-124, and HCFC-123 of 80, 10, and 1 pptv in the year 2010, mass conservation arguments imply an annually averaged global concentration of 0.16 μg/L if washout were the only removal mechanism for TFA. We present 3-D simulations of the HFC/HCFC precursors of TFA that include the rates of formation and deposition of TFA based on assumed future emissions. An established (GISS/Harvard/ UCI) but coarse-resolution (8° latitude by 10° longitude) chemical transport model was used. The annually averaged rainwater concentration of 0.12 μg/L (global) was calculated for the year 2010, when both washout and dry deposition are included as the loss mechanism for TFA from the atmosphere. For some large regions in midnorthern latitudes, values are larger, 0.15–0.20 μg/L. The highest monthly averaged rainwater concentrations of TFA for northern midlatitudes were calculated for the month of July, corresponding to 0.3–0.45 μg/L in parts of North America and Europe. Recent laboratory experiments have suggested that a substantial amount of vibrationally excited CF3CHFO is produced in the degradation of HFC-134a, decreasing the yield of TFA from this compound by 60%. This decrease would reduce the calculated amounts of TFA in rainwater in the year 2010 by 26%, for the same projected concentrations of precursors.

Published
1998

2. Simulation of summertime ozone over North America

Author

Jacob, Daniel J, Logan, Jennifer A, Yevich, Rose M, Gardner, Geraldine M, Spivakovsky, Clarisa M, Wofsy, Steven C, Munger, J. William, Sillman, Sanford, Prather, Michael J, Rodgers, Michael O, Westberg, Hal, and Zimmerman, Patrick R

Subjects
Eastern-United-States, tropospheric OH, reactive nitrogen, acid deposition, carbon-monoxide, sulfur-dioxide, oxidant model, chemistry, site, surface
Abstract

The concentrations of O3 and its precursors over North America are simulated for three summer months with a three-dimensional, continental-scale photochemical model using meteorological input from the Goddard Institute for Space Studies (GISS) general circulation model (GCM). The model has 4°×5° grid resolution and represents non linear chemistry in urban and industrial plumes with a subgrid nested scheme. Simulated median afternoon O3 concentrations at rural U.S. sites are within 5 ppb of observations in most cases, except in the south central United States where concentrations are overpredicted by 15–20 ppb. The model captures successfully the development of regional high-O3 episodes over the northeastern United States on the back side of weak, warm, stagnant anticyclones. Simulated concentrations of CO and nonmethane hydrocarbons are generally in good agreement with observations, concentrations of NOx are underpredicted by 10–30%, and concentrations of peroxyacylnitrates (PANs) are overpredicted by a factor of 2 to 3. The overprediction of PANs is attributed to flaws in the photochemical mechanism, including excessive production from oxidation of isoprene, and may also reflect an underestimate of PANs deposition. Subgrid nonlinear chemistry as captured by the nested plumes scheme decreases the net O3 production computed in the United States boundary layer by 8% on average.

Published
1993

3. Impacts of global emissions of CO, NO, and CH on China tropospheric hydroxyl free radicals.

Author

Su, Mingfeng, Lin, Yunping, Fan, Xinqiang, Peng, Li, and Zhao, Chunsheng

Subjects
*EMISSIONS (Air pollution), *CARBON monoxide, *FREE radicals, *SIMULATION methods & models, *NITRIC oxide, *METHANE
Abstract

Using the global chemistry and transport model MOZART, the simulated distributions of tropospheric hydroxyl free radicals (OH) over China and its sensitivities to global emissions of carbon monoxide (CO), nitrogen oxide (NO), and methane (CH) were investigated in this study. Due to various distributions of OH sources and sinks, the concentrations of tropospheric OH in east China are much greater than in west China. The contribution of NO + perhydroxyl radical (HO) reaction to OH production in east China is more pronounced than that in west China, and because of the higher reaction activity of non-methane volatile organic compounds (NMVOCs), the contributions to OH loss by NMVOCs exceed those of CO and take the dominant position in summer. The results of the sensitivity runs show a significant increase of tropospheric OH in east China from 1990 to 2000, and the trend continues. The positive effect of double emissions of NO on OH is partly offset by the contrary effect of increased CO and CH emissions: the double emissions of NO will cause an increase of OH of 18.1%-30.1%, while the increases of CO and CH will cause a decrease of OH of 12.2%-20.8% and 0.3%-3.0%, respectively. In turn, the lifetimes of CH, CO, and NO will increase by 0.3%-3.1% with regard to double emissions of CH, 13.9%-26.3% to double emissions of CO and decrease by 15.3%-23.2% to double emissions of NO. [ABSTRACT FROM AUTHOR]

Published
2012
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4. Observational evidence for interhemispheric hydroxyl-radical parity

Author

Paul J. Fraser, Paul B. Krummel, Masayuki Takigawa, Dale F. Hurst, Fred L. Moore, Tim Arnold, Kentaro Ishijima, L. P. Steele, Benjamin R. Lintner, H. J. Wang, Jens Mühle, Kazuyuki Miyazaki, Eric J. Hintsa, Ronald G. Prinn, Britton B. Stephens, A. Ghosh, Maarten Krol, Benjamin R. Miller, Simon O'Doherty, James W. Elkins, Elliot Atlas, S. C. Wofsy, Stephen A. Montzka, Ray F. Weiss, Bin Xiang, Dickon Young, and Prabir K. Patra

Subjects
Meteorologie en Luchtkwaliteit, Meteorology and Air Quality, tropospheric oh, methyl chloroform, chemistry, 7. Clean energy, Methane, chemistry.chemical_compound, Computer Simulation, climate, Southern Hemisphere, Air Pollutants, WIMEK, model, Multidisciplinary, Chloroform, Atmosphere, Hydroxyl Radical, variability, methane, atmospheric hydroxyl, Northern Hemisphere, sulfur-hexafluoride, Models, Theoretical, Sulfur hexafluoride, 13. Climate action, Environmental chemistry, Greenhouse gas, Atmospheric chemistry, transport, Nitrogen Oxides, Hydroxyl radical
Abstract

Observations of methyl chloroform combined with an atmospheric transport model predict a Northern to Southern Hemisphere hydroxyl ratio of slightly less than 1, whereas commonly used atmospheric chemistry models predict ratios 15–45% higher. The hydroxyl radical is an important atmospheric oxidant, but our knowledge of its global distribution remains imprecise, with estimates for the ratio of Northern Hemisphere to Southern Hemisphere hydroxyl radical concentration varying from 0.85 to 1.4. These authors use a three-dimensional chemistry-transport model that has been well validated for interhemispheric transport using sulphur hexafluoride measurements, to obtain an interhemispheric hydroxyl radical ratio of 0.97±0.12. This information can help improve our understanding of the fate of atmospheric pollutants and greenhouse gases. The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere1,2,3. The ratio of Northern Hemispheric to Southern Hemispheric (NH/SH) OH concentration is important for our understanding of emission estimates of atmospheric species such as nitrogen oxides and methane4,5,6. It remains poorly constrained, however, with a range of estimates from 0.85 to 1.4 (refs 4, 7,8,9,10). Here we determine the NH/SH ratio of OH with the help of methyl chloroform data (a proxy for OH concentrations) and an atmospheric transport model that accurately describes interhemispheric transport and modelled emissions. We find that for the years 2004–2011 the model predicts an annual mean NH–SH gradient of methyl chloroform that is a tight linear function of the modelled NH/SH ratio in annual mean OH. We estimate a NH/SH OH ratio of 0.97 ± 0.12 during this time period by optimizing global total emissions and mean OH abundance to fit methyl chloroform data from two surface-measurement networks and aircraft campaigns11,12,13. Our findings suggest that top-down emission estimates of reactive species such as nitrogen oxides in key emitting countries in the NH that are based on a NH/SH OH ratio larger than 1 may be overestimated.

Published
2014
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5. What can 14 CO measurements tell us about OH?

Subjects
c-14 production, Meteorologie en Luchtkwaliteit, WIMEK, model, Meteorology and Air Quality, tropospheric oh, atmospheric (co)-c-14, solar-cycle, transport, methyl chloroform, isotopic composition, cosmogenic (co)-c-14, chemistry
Abstract

The possible use of 14CO measurements to constrain hydroxyl radical (OH) concentrations in the atmosphere is investigated. 14CO is mainly produced in the upper atmosphere from cosmic radiation. Measurements of 14CO at the surface show lower concentrations compared to the upper atmospheric source region, which is the result of oxidation by OH. In this paper, the sensitivity of 14CO mixing ratio surface measurements to the 3-D OH distribution is assessed with the TM5 model. Simulated 14CO mixing ratios agree within a few molecules 14CO cm¿3 (STP) with existing measurements at five locations worldwide. The simulated cosmogenic 14CO distribution appears mainly sensitive to the assumed upper atmospheric 14C source function, and to a lesser extend to model resolution. As a next step, the sensitivity of 14CO measurements to OH is calculated with the adjoint TM5 model. The results indicate that 14CO measurements taken in the tropics are sensitive to OH in a spatially confined region that varies strongly over time due to meteorological variability. Given measurements with an accuracy of 0.5 molecules 14CO cm¿3 STP, a good characterization of the cosmogenic 14CO fraction, and assuming perfect transport modeling, a single 14CO measurement may constrain OH to 0.2¿0.3×106 molecules OH cm¿3 on time scales of 6 months and spatial scales of 70×70 degrees (latitude×longitude) between the surface and 500 hPa. The sensitivity of 14CO measurements to high latitude OH is about a factor of five higher. This is in contrast with methyl chloroform (MCF) measurements, which show the highest sensitivity to tropical OH, mainly due to the temperature dependent rate constant of the MCF¿OH reaction. A logical next step will be the analysis of existing 14CO measurements in an inverse modeling framework. This paper presents the required mathematical framework for such an analysis.

Published
2008

6. Small interannual variability of global atmospheric hydroxyl

Author

Montzka, S.A., Krol, M.C., Dlugokencky, E.J., Hall, B., Jöckel, P., Lelieveld, J., Marine and Atmospheric Research, Sub Atmospheric physics and chemistry, Dep Natuurkunde, Marine and Atmospheric Research, Sub Atmospheric physics and chemistry, and Dep Natuurkunde

Subjects
Meteorologie en Luchtkwaliteit, atmospheric chemistry, Ozone, 010504 meteorology & atmospheric sciences, Meteorology and Air Quality, tropospheric oh, Radical, methyl chloroform, atmospheric modeling, 010501 environmental sciences, Atmospheric sciences, chemistry, 01 natural sciences, Methane, Atmosphere, Troposphere, chemistry.chemical_compound, 0105 earth and related environmental sciences, abundance, Multidisciplinary, WIMEK, hydroxyl radical, capacity, carbon-monoxide, emissions, radicals, Trace gas, ozone, 13. Climate action, Atmospheric chemistry, oxidation capacity, (co)-c-14, Carbon monoxide
Abstract

The oxidizing capacity of the global atmosphere is largely determined by hydroxyl (OH) radicals and is diagnosed by analyzing methyl chloroform (CH(3)CCl(3)) measurements. Previously, large year-to-year changes in global mean OH concentrations have been inferred from such measurements, suggesting that the atmospheric oxidizing capacity is sensitive to perturbations by widespread air pollution and natural influences. We show how the interannual variability in OH has been more precisely estimated from CH(3)CCl(3) measurements since 1998, when atmospheric gradients of CH(3)CCl(3) had diminished as a result of the Montreal Protocol. We infer a small interannual OH variability as a result, indicating that global OH is generally well buffered against perturbations. This small variability is consistent with measurements of methane and other trace gases oxidized primarily by OH, as well as global photochemical model calculations.

Published
2011

7. What can 14 CO measurements tell us about OH?

Author

Krol, M.C., Meirink, J., Bergamaschi, P., Mak, J., and Lowe, D.

Subjects
Meteorologie en Luchtkwaliteit, c-14 production, WIMEK, model, Meteorology and Air Quality, tropospheric oh, solar-cycle, methyl chloroform, isotopic composition, chemistry, atmospheric (co)-c-14, transport, cosmogenic (co)-c-14
Abstract

The possible use of 14CO measurements to constrain hydroxyl radical (OH) concentrations in the atmosphere is investigated. 14CO is mainly produced in the upper atmosphere from cosmic radiation. Measurements of 14CO at the surface show lower concentrations compared to the upper atmospheric source region, which is the result of oxidation by OH. In this paper, the sensitivity of 14CO mixing ratio surface measurements to the 3-D OH distribution is assessed with the TM5 model. Simulated 14CO mixing ratios agree within a few molecules 14CO cm¿3 (STP) with existing measurements at five locations worldwide. The simulated cosmogenic 14CO distribution appears mainly sensitive to the assumed upper atmospheric 14C source function, and to a lesser extend to model resolution. As a next step, the sensitivity of 14CO measurements to OH is calculated with the adjoint TM5 model. The results indicate that 14CO measurements taken in the tropics are sensitive to OH in a spatially confined region that varies strongly over time due to meteorological variability. Given measurements with an accuracy of 0.5 molecules 14CO cm¿3 STP, a good characterization of the cosmogenic 14CO fraction, and assuming perfect transport modeling, a single 14CO measurement may constrain OH to 0.2¿0.3×106 molecules OH cm¿3 on time scales of 6 months and spatial scales of 70×70 degrees (latitude×longitude) between the surface and 500 hPa. The sensitivity of 14CO measurements to high latitude OH is about a factor of five higher. This is in contrast with methyl chloroform (MCF) measurements, which show the highest sensitivity to tropical OH, mainly due to the temperature dependent rate constant of the MCF¿OH reaction. A logical next step will be the analysis of existing 14CO measurements in an inverse modeling framework. This paper presents the required mathematical framework for such an analysis.

Published
2008

8. Inverse modeling of global and regional CH4 emissions using SCIAMACHY satellite retrievals

Author

Bergamaschi, P., Frankenberg, C., Meirink, J.F., Krol, M.C., Villani, M.G., Houweling, S., Dentener, F., Bergamaschi, P., Frankenberg, C., Meirink, J.F., Krol, M.C., Villani, M.G., Houweling, S., and Dentener, F.

Abstract

Methane retrievals from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument onboard ENVISAT provide important information on atmospheric CH4 sources, particularly in tropical regions which are poorly monitored by in situ surface observations. Recently, Frankenberg et al. (2008a, 2008b) reported a major revision of SCIAMACHY retrievals due to an update of spectroscopic parameters of water vapor and CH4. Here, we analyze the impact of this revision on global and regional CH4 emissions estimates in 2004, using the TM5-4DVAR inverse modeling system. Inversions based on the revised SCIAMACHY retrievals yield ~20% lower tropical emissions compared to the previous retrievals. The new retrievals improve significantly the consistency between observed and assimilated column average mixing ratios and the agreement with independent validation data. Furthermore, the considerable latitudinal and seasonal bias correction of the previous SCIAMACHY retrievals, derived in the TM5-4DVAR system by simultaneously assimilating high-accuracy surface measurements, is reduced by a factor of ~3. The inversions result in significant changes in the spatial patterns of emissions and their seasonality compared to the bottom-up inventories. Sensitivity tests were done to analyze the robustness of retrieved emissions, revealing some dependence on the applied a priori emission inventories and OH fields. Furthermore, we performed a detailed validation of simulated CH4 mixing ratios using NOAA ship and aircraft profile samples, as well as stratospheric balloon samples, showing overall good agreement. We use the new SCIAMACHY retrievals for a regional analysis of CH4 emissions from South America, Africa, and Asia, exploiting the zooming capability of the TM5 model. This allows a more detailed analysis of spatial emission patterns and better comparison with aircraft profiles and independent regional emission estimates available for South America. Large CH4 e

Published
2009

9. Simulation of summertime ozone over North America

Author

Daniel J. Jacob, Sanford Sillman, Rose M. Yevich, Jennifer A. Logan, Geraldine M. Gardner, C. M. Spivakovsky, Steven C. Wofsy, Michael O. Rodgers, Michael J. Prather, Patrick R. Zimmerman, J. William Munger, and Hal Westberg

Subjects
Atmospheric Science, Ozone, tropospheric OH, Reactive nitrogen, sulfur-dioxide, Eastern-United-States, Soil Science, reactive nitrogen, Aquatic Science, chemistry, Oceanography, chemistry.chemical_compound, Geochemistry and Petrology, Physical Sciences and Mathematics, acid deposition, site, Earth and Planetary Sciences (miscellaneous), surface, Isoprene, Earth-Surface Processes, Water Science and Technology, oxidant model, Ecology, Atmospheric models, carbon-monoxide, Paleontology, Forestry, Boundary layer, Geophysics, Space and Planetary Science, Anticyclone, Climatology, Atmospheric chemistry, Deposition (chemistry)
Abstract

The concentrations of O3 and its precursors over North America are simulated for three summer months with a three-dimensional, continental-scale photochemical model using meteorological input from the Goddard Institute for Space Studies (GISS) general circulation model (GCM). The model has 4°×5° grid resolution and represents non linear chemistry in urban and industrial plumes with a subgrid nested scheme. Simulated median afternoon O3 concentrations at rural U.S. sites are within 5 ppb of observations in most cases, except in the south central United States where concentrations are overpredicted by 15–20 ppb. The model captures successfully the development of regional high-O3 episodes over the northeastern United States on the back side of weak, warm, stagnant anticyclones. Simulated concentrations of CO and nonmethane hydrocarbons are generally in good agreement with observations, concentrations of NOx are underpredicted by 10–30%, and concentrations of peroxyacylnitrates (PANs) are overpredicted by a factor of 2 to 3. The overprediction of PANs is attributed to flaws in the photochemical mechanism, including excessive production from oxidation of isoprene, and may also reflect an underestimate of PANs deposition. Subgrid nonlinear chemistry as captured by the nested plumes scheme decreases the net O3 production computed in the United States boundary layer by 8% on average.

Published
1993

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