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Trifluoroacetic acid (TFA), a highly soluble and stable organic acid, is photochemically produced by certain anthropogenically emitted halocarbons such as HFC-134a and HFO-1234yf. Both these halocarbons are used as refrigerants in the automobile industry, and the high global warming potential of HFC-134a has promoted regulation of its use. Industries are transitioning to the use of HFO-1234yf as a more environmentally friendly alternative. We investigated the environmental effects of this change and found a 33-fold increase in the global burden of TFA from an annual value of 65 tonnes formed from the 2015 emissions of HFC-134a to a value of 2220 tonnes formed from an equivalent emission of HFO-1234yf. The percentage increase in surface TFA concentrations resulting from the switch from HFC-134a to HFO-1234yf remains substantial with an increase of up to 250-fold across Europe. The increase in emissions greater than the current emission scenario of HFO-1234yf is likely to result in significant TFA burden as the atmosphere is not able to disperse and deposit relevant oxidation products. The Criegee intermediate initiated loss process of TFA reduces the surface level atmospheric lifetime of TFA by up to 5 days (from 7 days to 2 days) in tropical forested regions.
Rayne Holland; M. Anwar H. Khan; Isabel Driscoll; Rabi Chhantyal-Pun; Richard G. Derwent; Craig A. Taatjes; Andrew J. Orr-Ewing; Carl J. Percival; Dudley E. Shallcross. Investigation of the Production of Trifluoroacetic Acid from Two Halocarbons, HFC-134a and HFO-1234yf and Its Fates Using a Global Three-Dimensional Chemical Transport Model. ACS Earth and Space Chemistry 2021, 5, 849 -857.
AMA StyleRayne Holland, M. Anwar H. Khan, Isabel Driscoll, Rabi Chhantyal-Pun, Richard G. Derwent, Craig A. Taatjes, Andrew J. Orr-Ewing, Carl J. Percival, Dudley E. Shallcross. Investigation of the Production of Trifluoroacetic Acid from Two Halocarbons, HFC-134a and HFO-1234yf and Its Fates Using a Global Three-Dimensional Chemical Transport Model. ACS Earth and Space Chemistry. 2021; 5 (4):849-857.
Chicago/Turabian StyleRayne Holland; M. Anwar H. Khan; Isabel Driscoll; Rabi Chhantyal-Pun; Richard G. Derwent; Craig A. Taatjes; Andrew J. Orr-Ewing; Carl J. Percival; Dudley E. Shallcross. 2021. "Investigation of the Production of Trifluoroacetic Acid from Two Halocarbons, HFC-134a and HFO-1234yf and Its Fates Using a Global Three-Dimensional Chemical Transport Model." ACS Earth and Space Chemistry 5, no. 4: 849-857.
The measurement of acetic acid during the ClearfLo campaign for Winter 2012 and Summer 2012 in London and at the Weybourne Research Station (East Anglia), UK for Spring 2013 gives the average ± 1σ mixing ratios of 45.9 ± 31.5, 25.7 ± 14.3 and 55.1 ± 32.0 ppt, respectively. The WRF-Chem-CRI model was run over these three seasons and within uncertainty reproduced the data from London, with mixing ratios during Winter (32.3 ± 25.3 ppt) and Summer (55.1 ± 22.6 ppt). The model's seasonality was opposite to that observed and although within the combined uncertainty of the measurement and model data it underpredicted the levels observed at Weybourne during Spring (28.9 ± 19.3 ppt). The model-measurement correlations of the meteorological parameters (e.g. temperature, wind direction, wind speed) were good with a correlation of R > 0.7. The predicted diurnal trend of acetic acid resembled measurement data with a small negative bias during winter but performed less well during summer with a large positive bias and in spring with a large negative bias. The reasonable correlation of acetic acid mixing ratios with temperature was found to be similar for both measurement and model (Rmeasurement = 0.5, Rmodel = 0.6) during Summer suggesting the importance of the photochemical secondary source of acetic acid which was reflected both in the measurement and the model. The key processes identified from the model results were a) missing direct anthropogenic sources of acetic acid (accounting for the lower model winter values) and b) not including its loss process by Criegee intermediates (accounting for the higher model values in summer). Comparing the weekend data with weekday data revealed a likely underpredicted source of acetic acid from vehicles. The wet deposition removal process of acetic acid was found not to be as significant in the UK as anticipated.
M. Anwar H. Khan; James W. Dennis; Thomas J. Bannan; Asan Bacak; Alastair M. Booth; Jennifer B.A. Muller; Douglas Lowe; Carl J. Percival; Dudley E. Shallcross. Tropospheric modeling of acetic acid in the UK for Summer, Winter and Spring seasons using a mesoscale 3-dimensional chemistry and transport model, WRF-Chem-CRI. Atmospheric Research 2021, 254, 105506 .
AMA StyleM. Anwar H. Khan, James W. Dennis, Thomas J. Bannan, Asan Bacak, Alastair M. Booth, Jennifer B.A. Muller, Douglas Lowe, Carl J. Percival, Dudley E. Shallcross. Tropospheric modeling of acetic acid in the UK for Summer, Winter and Spring seasons using a mesoscale 3-dimensional chemistry and transport model, WRF-Chem-CRI. Atmospheric Research. 2021; 254 ():105506.
Chicago/Turabian StyleM. Anwar H. Khan; James W. Dennis; Thomas J. Bannan; Asan Bacak; Alastair M. Booth; Jennifer B.A. Muller; Douglas Lowe; Carl J. Percival; Dudley E. Shallcross. 2021. "Tropospheric modeling of acetic acid in the UK for Summer, Winter and Spring seasons using a mesoscale 3-dimensional chemistry and transport model, WRF-Chem-CRI." Atmospheric Research 254, no. : 105506.
Recent revisions to our understanding of the oxidation chemistry of isoprene have been incorporated into a well-established global atmospheric chemistry and transport model, STOCHEM-CRI. These revisions have previously been shown to increase the production and recycling of HOx radicals at lower NOx levels characteristic of the remote troposphere. The main aim of this study is to assess the resultant broader changes to atmospheric composition due to the recent revisions to isoprene oxidation chemistry. The impact of the increased isoprene-related HOx recycling is found to be significant on the reduction of volatile organic compounds (VOCs) lifetime, e.g. a decrease in isoprene's tropospheric burden by ∼17%. The analysis of lifetime reduction of the potent greenhouse gas, methane, associated with the increased HOx recycling, suggests its significant lifetime reduction by ∼5% in terms of the current literature. The revisions to the isoprene chemistry also reduce the amount of ozone (by up to 10%), but provide a significant increase in NO3 (by up to 30%) over equatorial forested regions, which can alter the oxidizing capacity of the troposphere. The calculated mixing ratios of formic acid are decreased which in turn leads to an increase in the inferred concentrations of Criegee intermediates due to reduced loss through reaction with formic acid (up to 80%) over the dominant isoprene emitting regions.
M. Anwar H. Khan; Billie-Louise Schlich; Michael E. Jenkin; Michael C. Cooke; Richard G. Derwent; Jessica L. Neu; Carl J. Percival; Dudley E. Shallcross. Changes to simulated global atmospheric composition resulting from recent revisions to isoprene oxidation chemistry. Atmospheric Environment 2020, 244, 117914 .
AMA StyleM. Anwar H. Khan, Billie-Louise Schlich, Michael E. Jenkin, Michael C. Cooke, Richard G. Derwent, Jessica L. Neu, Carl J. Percival, Dudley E. Shallcross. Changes to simulated global atmospheric composition resulting from recent revisions to isoprene oxidation chemistry. Atmospheric Environment. 2020; 244 ():117914.
Chicago/Turabian StyleM. Anwar H. Khan; Billie-Louise Schlich; Michael E. Jenkin; Michael C. Cooke; Richard G. Derwent; Jessica L. Neu; Carl J. Percival; Dudley E. Shallcross. 2020. "Changes to simulated global atmospheric composition resulting from recent revisions to isoprene oxidation chemistry." Atmospheric Environment 244, no. : 117914.
In the context of tropospheric chemistry, Criegee intermediates denote carbonyl oxides with biradical/zwitterionic character (R1R2COO) that form during the ozonolysis of alkenes. First discovered almost 70 years ago, stabilised versions of Criegee intermediates formed via collisional removal of excess energy have interesting kinetic and mechanistic properties. The direct production and detection of these intermediates were not reported in the literature until 2008. However, recent advances in their generation through the ultraviolet irradiation of the corresponding diiodoalkanes in excess O2 and detection by various spectroscopic techniques (photoionisation, ultraviolet, infrared, microwave and mass spectrometry) have shown that these species can react rapidly with closed-shell molecules, in many cases at or exceeding the classical gas-kinetic limit, via multiple reaction pathways. These reactions can be complex, and laboratory measurements of products and the temperature and pressure dependence of the reaction kinetics have also revealed unusual behaviour. The potential role of these intermediates in atmospheric chemistry is significant, altering models of the oxidising capacity of the Earth's atmosphere and the rate of generation of secondary organic aerosol.
Rabi Chhantyal-Pun; M. Anwar H. Khan; Craig A. Taatjes; Carl J. Percival; Andrew J. Orr-Ewing; Dudley E. Shallcross. Criegee intermediates: production, detection and reactivity. International Reviews in Physical Chemistry 2020, 39, 385 -424.
AMA StyleRabi Chhantyal-Pun, M. Anwar H. Khan, Craig A. Taatjes, Carl J. Percival, Andrew J. Orr-Ewing, Dudley E. Shallcross. Criegee intermediates: production, detection and reactivity. International Reviews in Physical Chemistry. 2020; 39 (3):385-424.
Chicago/Turabian StyleRabi Chhantyal-Pun; M. Anwar H. Khan; Craig A. Taatjes; Carl J. Percival; Andrew J. Orr-Ewing; Dudley E. Shallcross. 2020. "Criegee intermediates: production, detection and reactivity." International Reviews in Physical Chemistry 39, no. 3: 385-424.
Nonacyl peroxy nitrates, RO2NO2, act as a reservoir species for NOx in the upper troposphere. The low thermal stability of these compounds means that they only become a significant sink of NOx at the low temperatures observed in the upper troposphere. The chemical processes involved with the formation and degradation of methyl peroxy nitrate (CH3O2NO2) and an additional 44 RO2NO2 have been incorporated into the global three-dimensional chemical transport model, STOCHEM-CRI. The study investigates the effect of the addition of RO2NO2 chemistry on the budget of NOx, which in turn impacts the ozone, hydroxyl radical (OH), and nitrate radical (NO3) formation. This investigation found that the addition of CH3O2NO2 led to an increase in the tropospheric burdens of NOx (+3.0%), ozone (+2.0%), OH (+4.0%), and NO3 (+8.8%). However, the other 44 RO2NO2 contribute a significant increment of tropospheric global burdens of NOx (+4.4%), ozone (+3.4%), OH (+5.5%), and NO3 (+11.1%) with the largest mixing ratios of NOx of up to 25%, ozone up to 14%, OH up to 20%, and NO3 up to 50%. The increase in the global burden of oxidizing species such as OH due to the addition of 44 other RO2NO2 led to a significant decrease in the lifetimes of greenhouse gases such as methane (∼6%). The modeled mixing ratios of CH3O2NO2 were in reasonable agreement with measurements, the only extensive data set available.
M. Anwar H. Khan; Barnaby Miles; Michael E. Jenkin; Richard G. Derwent; Carl J. Percival; Dudley E. Shallcross. Investigating the Impacts of Nonacyl Peroxy Nitrates on the Global Composition of the Troposphere Using a 3-D Chemical Transport Model, STOCHEM-CRI. ACS Earth and Space Chemistry 2020, 4, 1201 -1212.
AMA StyleM. Anwar H. Khan, Barnaby Miles, Michael E. Jenkin, Richard G. Derwent, Carl J. Percival, Dudley E. Shallcross. Investigating the Impacts of Nonacyl Peroxy Nitrates on the Global Composition of the Troposphere Using a 3-D Chemical Transport Model, STOCHEM-CRI. ACS Earth and Space Chemistry. 2020; 4 (7):1201-1212.
Chicago/Turabian StyleM. Anwar H. Khan; Barnaby Miles; Michael E. Jenkin; Richard G. Derwent; Carl J. Percival; Dudley E. Shallcross. 2020. "Investigating the Impacts of Nonacyl Peroxy Nitrates on the Global Composition of the Troposphere Using a 3-D Chemical Transport Model, STOCHEM-CRI." ACS Earth and Space Chemistry 4, no. 7: 1201-1212.
Previous work regarding the behaviour of ozone surface concentrations over many years in the United Kingdom had predicted that the frequency and severity of ozone episodes would become less marked in the future as a response to environmental regulations. The aim of this study is to extend these studies and compare the results with their predictions. The ozone data of 13 rural and six urban sites in the UK collected from the Department for Environment, Food and Rural Affairs over a period from 1992 to mid-2019 were used to investigate this behaviour. The yearly ozone exceedances (the number of hours that the ozone concentration exceeded the 50 ppbv limit) in the United Kingdom were found to have decreased over the last 30 years regardless of the type of site (rural or urban), showing that the adopted emission controls have so far been successful in the abatement of pollutant emissions. In the past three decades, the highest numbers of exceedances were reached in May regardless of the type of site. Furthermore, these episodes have become less frequent and less severe in recent years. In fact, the number of hours of exceedance is lower than that in previous decades, and it is almost constant throughout the week.
Florencia M. R. Diaz; M. Anwar H. Khan; Beth M. A. Shallcross; Esther D. G. Shallcross; Ulrich Vogt; Dudley E. Shallcross. Ozone Trends in the United Kingdom over the Last 30 Years. Atmosphere 2020, 11, 534 .
AMA StyleFlorencia M. R. Diaz, M. Anwar H. Khan, Beth M. A. Shallcross, Esther D. G. Shallcross, Ulrich Vogt, Dudley E. Shallcross. Ozone Trends in the United Kingdom over the Last 30 Years. Atmosphere. 2020; 11 (5):534.
Chicago/Turabian StyleFlorencia M. R. Diaz; M. Anwar H. Khan; Beth M. A. Shallcross; Esther D. G. Shallcross; Ulrich Vogt; Dudley E. Shallcross. 2020. "Ozone Trends in the United Kingdom over the Last 30 Years." Atmosphere 11, no. 5: 534.
Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester, J. Chem. Phys. 149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only the syn-conformers are observed; anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction of syn-MVK-oxide with SO2 and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO3 and identifying organic hydroperoxide formation from reaction with SO2 and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.
Rebecca L. Caravan; Michael F. Vansco; Kendrew Au; M. Anwar H. Khan; Yu-Lin Li; Frank A. F. Winiberg; Kristen Zuraski; Yen-Hsiu Lin; Wen Chao; Nisalak Trongsiriwat; Patrick J. Walsh; David L. Osborn; Carl J. Percival; Jim Jr-Min Lin; Dudley E. Shallcross; Leonid Sheps; Stephen J. Klippenstein; Craig A. Taatjes; Marsha I. Lester. Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate. Proceedings of the National Academy of Sciences 2020, 117, 9733 -9740.
AMA StyleRebecca L. Caravan, Michael F. Vansco, Kendrew Au, M. Anwar H. Khan, Yu-Lin Li, Frank A. F. Winiberg, Kristen Zuraski, Yen-Hsiu Lin, Wen Chao, Nisalak Trongsiriwat, Patrick J. Walsh, David L. Osborn, Carl J. Percival, Jim Jr-Min Lin, Dudley E. Shallcross, Leonid Sheps, Stephen J. Klippenstein, Craig A. Taatjes, Marsha I. Lester. Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate. Proceedings of the National Academy of Sciences. 2020; 117 (18):9733-9740.
Chicago/Turabian StyleRebecca L. Caravan; Michael F. Vansco; Kendrew Au; M. Anwar H. Khan; Yu-Lin Li; Frank A. F. Winiberg; Kristen Zuraski; Yen-Hsiu Lin; Wen Chao; Nisalak Trongsiriwat; Patrick J. Walsh; David L. Osborn; Carl J. Percival; Jim Jr-Min Lin; Dudley E. Shallcross; Leonid Sheps; Stephen J. Klippenstein; Craig A. Taatjes; Marsha I. Lester. 2020. "Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate." Proceedings of the National Academy of Sciences 117, no. 18: 9733-9740.
Perfluorooctanoic acid, PFOA, is one of the many concerning pollutants in our atmosphere; it is highly resistant to environmental degradation processes, which enables it to accumulate biologically. With direct routes of this chemical to the environment decreasing, as a consequence of the industrial phase out of PFOA, it has become more important to accurately model the effects of indirect production routes, such as environmental degradation of precursors; e.g., fluorotelomer alcohols (FTOHs). The study reported here investigates the chemistry, physical loss and transport of PFOA and its precursors, FTOHs, throughout the troposphere using a 3D global chemical transport model, STOCHEM-CRI. Moreover, this investigation includes an important loss process of PFOA in the atmosphere via the addition of the stabilised Criegee intermediates, hereby referred to as the “Criegee Field.” Whilst reaction with Criegee intermediates is a significant atmospheric loss process of PFOA, it does not result in its permanent removal from the atmosphere. The atmospheric fate of the resultant hydroperoxide product from the reaction of PFOA and Criegee intermediates resulted in a ≈0.04 Gg year−1 increase in the production flux of PFOA. Furthermore, the physical loss of the hydroperoxide product from the atmosphere (i.e., deposition), whilst decreasing the atmospheric concentration, is also likely to result in the reformation of PFOA in environmental aqueous phases, such as clouds, precipitation, oceans and lakes. As such, removal facilitated by the “Criegee Field” is likely to simply result in the acceleration of PFOA transfer to the surface (with an expected decrease in PFOA atmospheric lifetime of ≈10 h, on average from ca. 80 h without Criegee loss to 70 h with Criegee loss).
Rayne Holland; M. Anwar H. Khan; Rabi Chhantyal-Pun; Andrew J. Orr-Ewing; Carl J. Percival; Craig A. Taatjes; Dudley E. Shallcross. Investigating the Atmospheric Sources and Sinks of Perfluorooctanoic Acid Using a Global Chemistry Transport Model. Atmosphere 2020, 11, 407 .
AMA StyleRayne Holland, M. Anwar H. Khan, Rabi Chhantyal-Pun, Andrew J. Orr-Ewing, Carl J. Percival, Craig A. Taatjes, Dudley E. Shallcross. Investigating the Atmospheric Sources and Sinks of Perfluorooctanoic Acid Using a Global Chemistry Transport Model. Atmosphere. 2020; 11 (4):407.
Chicago/Turabian StyleRayne Holland; M. Anwar H. Khan; Rabi Chhantyal-Pun; Andrew J. Orr-Ewing; Carl J. Percival; Craig A. Taatjes; Dudley E. Shallcross. 2020. "Investigating the Atmospheric Sources and Sinks of Perfluorooctanoic Acid Using a Global Chemistry Transport Model." Atmosphere 11, no. 4: 407.
A global chemistry-transport model has been employed to describe the global sources and sinks of hydrogen (H2) and its isotopomer (HD). The model is able to satisfactorily describe the observed tropospheric distributions of H2 and HD and deliver budgets and turnovers which agree with literature studies. We than go on to quantify the methane and ozone responses to emission pulses of hydrogen and their likely radiative forcing consequences. These radiative forcing consequences have been expressed on a 1 Tg basis and integrated over a hundred-year time horizon. When compared to the consequences of a 1 Tg emission pulse of carbon dioxide, 1 Tg of hydrogen causes 5 ± 1 times as much time-integrated radiative forcing over a hundred-year time horizon. That is to say, hydrogen has a global warming potential (GWP) of 5 ± 1 over a hundred-year time horizon. The global warming consequences of a hydrogen-based low-carbon energy system therefore depend critically on the hydrogen leakage rate. If the leakage of hydrogen from all stages in the production, distribution, storage and utilisation of hydrogen is efficiently curtailed, then hydrogen-based energy systems appear to be an attractive proposition in providing a future replacement for fossil-fuel based energy systems.
Richard G. Derwent; David S. Stevenson; Steven R. Utembe; Michael E. Jenkin; Anwar H. Khan; Dudley E. Shallcross. Global modelling studies of hydrogen and its isotopomers using STOCHEM-CRI: Likely radiative forcing consequences of a future hydrogen economy. International Journal of Hydrogen Energy 2020, 45, 9211 -9221.
AMA StyleRichard G. Derwent, David S. Stevenson, Steven R. Utembe, Michael E. Jenkin, Anwar H. Khan, Dudley E. Shallcross. Global modelling studies of hydrogen and its isotopomers using STOCHEM-CRI: Likely radiative forcing consequences of a future hydrogen economy. International Journal of Hydrogen Energy. 2020; 45 (15):9211-9221.
Chicago/Turabian StyleRichard G. Derwent; David S. Stevenson; Steven R. Utembe; Michael E. Jenkin; Anwar H. Khan; Dudley E. Shallcross. 2020. "Global modelling studies of hydrogen and its isotopomers using STOCHEM-CRI: Likely radiative forcing consequences of a future hydrogen economy." International Journal of Hydrogen Energy 45, no. 15: 9211-9221.
Benzene and toluene, emitted into the atmosphere from a number of common anthropogenic activities, pose a significant human health risk. The mole fractions of toluene and benzene were measured at two urban locations (Foreshore and Potsdam) in Cape Town and one background site at Cape Point, South Africa over the period of July-November 2017. The analysis of the mole fractions of benzene and toluene at two sampling sites in the city of Cape Town gave an indication of the probable anthropogenic sources of the air masses sampled at these sites. We propose that a traffic source dominated at the Foreshore site, while industrial processes dominated at the Potsdam site. The analysis of wind rose plots of benzene and toluene and the elevated mole fractions observed at the remote “clean air” sampling site, Cape Point, suggest that polluted air from Cape Town is the major source of the benzene and toluene mole fractions observed at Cape Point. Hydroxyl (OH) radical concentrations were estimated for Cape Town from the difference in T/B ([toluene]/[benzene]) ratios between Cape Town and Cape Point. The Cape Town OH estimations displayed a mean of (7.2 ± 3.5) 106 molecules cm-3 at the Foreshore site and (9.1 ± 4.4) 106 molecules cm-3 at the Potsdam site, without consideration of dilution reducing to (5.4 ± 3.4) 106 molecules cm-3 for the Foreshore site and (7.4 ± 4.6) 106 molecules cm-3 for Potsdam site for the period of July-November 2017 when dilution was considered. The estimated Cape Town OH concentrations are on the high side, but consistent with the results from other urban studies and may suggest a role for OH recycling following biogenic emissions between Cape Town and Cape Point.
Brett Kuyper; Haithum Wingrove; Timothy Lesch; Casper Labuschagne; Daniel Say; Damien Martin; Dickon Young; M. Anwar H. Khan; Simon O'doherty; Michael Trevor Davies-Coleman; Dudley E. Shallcross. Atmospheric Toluene and Benzene Mole Fractions at Cape Town and Cape Point and an Estimation of the Hydroxyl Radical Concentrations in the Air above the Cape Peninsula, South Africa. ACS Earth and Space Chemistry 2019, 4, 24 -34.
AMA StyleBrett Kuyper, Haithum Wingrove, Timothy Lesch, Casper Labuschagne, Daniel Say, Damien Martin, Dickon Young, M. Anwar H. Khan, Simon O'doherty, Michael Trevor Davies-Coleman, Dudley E. Shallcross. Atmospheric Toluene and Benzene Mole Fractions at Cape Town and Cape Point and an Estimation of the Hydroxyl Radical Concentrations in the Air above the Cape Peninsula, South Africa. ACS Earth and Space Chemistry. 2019; 4 (1):24-34.
Chicago/Turabian StyleBrett Kuyper; Haithum Wingrove; Timothy Lesch; Casper Labuschagne; Daniel Say; Damien Martin; Dickon Young; M. Anwar H. Khan; Simon O'doherty; Michael Trevor Davies-Coleman; Dudley E. Shallcross. 2019. "Atmospheric Toluene and Benzene Mole Fractions at Cape Town and Cape Point and an Estimation of the Hydroxyl Radical Concentrations in the Air above the Cape Peninsula, South Africa." ACS Earth and Space Chemistry 4, no. 1: 24-34.
Ammonia (NH3) is a basic gas of significant atmospheric interest because of its role in the possible formation of fine particulates and because it is a source of fixed nitrogen in soils and plants. NH3 processing in the atmosphere has been simulated using two 3-D models: the global chemistry transport model, STOCHEM-CRI and the regional coupled meteorological-chemical model, WRF-Chem-CRI. From analysis of STOCHEM-CRI simulations, NH3 removal fluxes of dry deposition (24.6 Tg(N)/yr), wet deposition (20.8 Tg(N)/yr), NH4+ formation (25.6 Tg(N)/yr) and reaction with OH (1.7 Tg(N)/yr) have been calculated, making a global annual average burden of 0.22 Tg(N) and life-time of 1.1 days. The gas-phase loss by OH, NO3 and stabilized Criegee intermediates contribute 2.3%, <1% and < 1%, respectively to the total global loss of tropospheric NH3. The highest concentrations of NH3 are found to be in the region of South and East Asia, which are associated mostly with agricultural NH3 emissions. Loss of surface NH3 by reaction with OH increases by up to 25% along the equator because of the abundances of ozone. Comparison of satellite observations and model results give a better understanding of the temporal and spatial variations of atmospheric NH3 on a global and regional scales. Using the anthropogenic seasonal NH3 emission class in the model gives a poor representation of seasonal NH3. The positive bias in Africa and South America for all seasons is likely due to undetermined sources in the model such as underestimated biomass burning emissions of NH3 adopted in the model. The regional model results over North-West Europe during summer months are biased low compared with the measurements- suggesting either missing sources, or too efficient loss processes in the region.
M Anwar H Khan; D. Lowe; R.G. Derwent; Amy Foulds; R. Chhantyal-Pun; G. McFiggans; Andrew Orr-Ewing; C.J. Percival; D.E. Shallcross. Global and regional model simulations of atmospheric ammonia. Atmospheric Research 2019, 234, 104702 .
AMA StyleM Anwar H Khan, D. Lowe, R.G. Derwent, Amy Foulds, R. Chhantyal-Pun, G. McFiggans, Andrew Orr-Ewing, C.J. Percival, D.E. Shallcross. Global and regional model simulations of atmospheric ammonia. Atmospheric Research. 2019; 234 ():104702.
Chicago/Turabian StyleM Anwar H Khan; D. Lowe; R.G. Derwent; Amy Foulds; R. Chhantyal-Pun; G. McFiggans; Andrew Orr-Ewing; C.J. Percival; D.E. Shallcross. 2019. "Global and regional model simulations of atmospheric ammonia." Atmospheric Research 234, no. : 104702.
Brett Kuyper; Timothy Lesch; Casper Labuschagne; Damien Martin; Dickon Young; M. Anwar H. Khan; Alastair G. Williams; Simon O'Doherty; Michael T. Davies-Coleman; Dudley E. Shallcross. Volatile halocarbon measurements in the marine boundary layer at Cape Point, South Africa. Atmospheric Environment 2019, 214, 1 .
AMA StyleBrett Kuyper, Timothy Lesch, Casper Labuschagne, Damien Martin, Dickon Young, M. Anwar H. Khan, Alastair G. Williams, Simon O'Doherty, Michael T. Davies-Coleman, Dudley E. Shallcross. Volatile halocarbon measurements in the marine boundary layer at Cape Point, South Africa. Atmospheric Environment. 2019; 214 ():1.
Chicago/Turabian StyleBrett Kuyper; Timothy Lesch; Casper Labuschagne; Damien Martin; Dickon Young; M. Anwar H. Khan; Alastair G. Williams; Simon O'Doherty; Michael T. Davies-Coleman; Dudley E. Shallcross. 2019. "Volatile halocarbon measurements in the marine boundary layer at Cape Point, South Africa." Atmospheric Environment 214, no. : 1.
The purpose of this paper is to discuss ways that a chemistry course could reposition itself by adopting interdisciplinary approaches based on systems thinking and the Sustainable Development Goals (SDGs) as overarching frameworks, to give an overview of several challenges that chemistry in higher education is facing, and to discuss how those can be addressed as a result of this repositioning. We will be discussing the need for a new type of scientist, one who has a deep understanding of their own discipline but also an overview of the links with other disciplines and is equipped with skills that will help them contribute to the solutions of a very complex system: the human–environment interaction system. Chemists should be part of what is described by earth systems’ science as “the new social contract” between science and society. Finally, we will explore how this can be reflected in the curricula of higher education, and we will present a University of Bristol educational initiative, Bristol Futures, that attempts to address this.
Eleni Michalopoulou; Dudley E. Shallcross; Ed Atkins; Aisling Tierney; Nicholas C. Norman; Chris Preist; Simon O’Doherty; Rebecca Saunders; Alexander Birkett; Chris Willmore; Ioannis Ninos. The End of Simple Problems: Repositioning Chemistry in Higher Education and Society Using a Systems Thinking Approach and the United Nations’ Sustainable Development Goals as a Framework. Journal of Chemical Education 2019, 96, 2825 -2835.
AMA StyleEleni Michalopoulou, Dudley E. Shallcross, Ed Atkins, Aisling Tierney, Nicholas C. Norman, Chris Preist, Simon O’Doherty, Rebecca Saunders, Alexander Birkett, Chris Willmore, Ioannis Ninos. The End of Simple Problems: Repositioning Chemistry in Higher Education and Society Using a Systems Thinking Approach and the United Nations’ Sustainable Development Goals as a Framework. Journal of Chemical Education. 2019; 96 (12):2825-2835.
Chicago/Turabian StyleEleni Michalopoulou; Dudley E. Shallcross; Ed Atkins; Aisling Tierney; Nicholas C. Norman; Chris Preist; Simon O’Doherty; Rebecca Saunders; Alexander Birkett; Chris Willmore; Ioannis Ninos. 2019. "The End of Simple Problems: Repositioning Chemistry in Higher Education and Society Using a Systems Thinking Approach and the United Nations’ Sustainable Development Goals as a Framework." Journal of Chemical Education 96, no. 12: 2825-2835.
Mounting evidence suggests that Criegee intermediates are important tropospheric oxidants of both organic and inorganic gases, supplementing the oxidation chemistry initiated by OH radicals. Here, the rate coefficient for reaction of the simplest Criegee intermediate CH2OO with acetone, k(CH2OO + (CH3)2CO), was measured using laser flash photolysis and cavity ring-down spectroscopy methods under tropospherically relevant conditions of pressure and temperature. The pressure dependence of k(CH2OO + (CH3)2CO)= (4.7 ± 0.1) × 10-13 [N2] / ((3.7 ± 1.4) × 1016 + [N2]) cm3s-1 was measured in the 5 to 100 Torr range, returning a high-pressure limit value of (4.7 ± 0.1) × 10-13 cm3molecule-1 s-1 at 293 K. A temperature dependence of k(CH2OO + (CH3)2CO) = (1.4 ± 0.2) × 10-21 T2 exp (2410 ± 40 / T) cm3molecule-1 s-1 was observed in the 250 to 310 K range. The global chemical transport model (STOCHEM-CRI) was used to model the speciated Criegee intermediate field using recently reported temperature dependent rate coefficient values for various reactions of Criegee intermediates. Incorporation of the Criegee intermediate reaction with acetone in the model predicts decreases in acetone concentration of as much as 10 to 40 ppt in various regions of the world.
Rabi Chhantyal-Pun; M. Anwar H. Khan; Rebecca Martin; Nicholas Zachhuber; Zachary J. Buras; Carl J. Percival; Dudley E. Shallcross; Andrew J. Orr-Ewing. Direct Kinetic and Atmospheric Modeling Studies of Criegee Intermediate Reactions with Acetone. ACS Earth and Space Chemistry 2019, 3, 2363 -2371.
AMA StyleRabi Chhantyal-Pun, M. Anwar H. Khan, Rebecca Martin, Nicholas Zachhuber, Zachary J. Buras, Carl J. Percival, Dudley E. Shallcross, Andrew J. Orr-Ewing. Direct Kinetic and Atmospheric Modeling Studies of Criegee Intermediate Reactions with Acetone. ACS Earth and Space Chemistry. 2019; 3 (10):2363-2371.
Chicago/Turabian StyleRabi Chhantyal-Pun; M. Anwar H. Khan; Rebecca Martin; Nicholas Zachhuber; Zachary J. Buras; Carl J. Percival; Dudley E. Shallcross; Andrew J. Orr-Ewing. 2019. "Direct Kinetic and Atmospheric Modeling Studies of Criegee Intermediate Reactions with Acetone." ACS Earth and Space Chemistry 3, no. 10: 2363-2371.
Thomas J. Bannan; M. Anwar H. Khan; Michael Le Breton; Michael Priestley; Stephen D. Worrall; Asan Bacak; Nicholas A. Marsden; Douglas Lowe; Joe Pitt; Grant Allen; David Topping; Hugh Coe; Gordon McFiggans; Dudley E. Shallcross; Carl J. Percival. A Large Source of Atomic Chlorine From ClNO 2 Photolysis at a U.K. Landfill Site. Geophysical Research Letters 2019, 46, 8508 -8516.
AMA StyleThomas J. Bannan, M. Anwar H. Khan, Michael Le Breton, Michael Priestley, Stephen D. Worrall, Asan Bacak, Nicholas A. Marsden, Douglas Lowe, Joe Pitt, Grant Allen, David Topping, Hugh Coe, Gordon McFiggans, Dudley E. Shallcross, Carl J. Percival. A Large Source of Atomic Chlorine From ClNO 2 Photolysis at a U.K. Landfill Site. Geophysical Research Letters. 2019; 46 (14):8508-8516.
Chicago/Turabian StyleThomas J. Bannan; M. Anwar H. Khan; Michael Le Breton; Michael Priestley; Stephen D. Worrall; Asan Bacak; Nicholas A. Marsden; Douglas Lowe; Joe Pitt; Grant Allen; David Topping; Hugh Coe; Gordon McFiggans; Dudley E. Shallcross; Carl J. Percival. 2019. "A Large Source of Atomic Chlorine From ClNO 2 Photolysis at a U.K. Landfill Site." Geophysical Research Letters 46, no. 14: 8508-8516.
The behaviour of the CRI-MECH chemistry scheme was investigated over North-West Europe for the first week of each month for the year of 2015 using the mesoscale non-hydrostatic 3-D meteorological model, WRF-Chem. The model simulations of the distribution of important trace gas species (e.g. ozone, CO, NO, NO2 and SO2) were compared with ground-based measurements of selected rural and urban areas in UK. The model validation using the UK Defra Automatic Urban and Rural Network (AURN) measured data from sites across the UK showed a reasonable agreement between model-measurement for ozone (R = 0.45 for rural sites and R = 0.34 for urban sites), for NO2 (R = 0.65 for rural sites and R = 0.45 for urban sites) and for NO (R = 0.35 for rural sites and R = 0.22 for urban sites). However, a poor correlation between model-measurement is found for CO (R = 0.15 for urban sites) and for SO2 (R = 0.1 for rural sites and R = 0.27 for urban sites). Further investigations showed a poorer performance of the model ozone, CO, NO and NO2 during summer and autumn months compared with winter months. The differences in model performance were most noticeable for ozone with the other species having more variance between sites and months. The possible causes for the deviations between the modelled and the measured data are discussed.
M.A.H. Khan; J. Clements; D. Lowe; G. McFiggans; C.J. Percival; D.E. Shallcross. Investigating the behaviour of the CRI-MECH gas-phase chemistry scheme on a regional scale for different seasons using the WRF-Chem model. Atmospheric Research 2019, 229, 145 -156.
AMA StyleM.A.H. Khan, J. Clements, D. Lowe, G. McFiggans, C.J. Percival, D.E. Shallcross. Investigating the behaviour of the CRI-MECH gas-phase chemistry scheme on a regional scale for different seasons using the WRF-Chem model. Atmospheric Research. 2019; 229 ():145-156.
Chicago/Turabian StyleM.A.H. Khan; J. Clements; D. Lowe; G. McFiggans; C.J. Percival; D.E. Shallcross. 2019. "Investigating the behaviour of the CRI-MECH gas-phase chemistry scheme on a regional scale for different seasons using the WRF-Chem model." Atmospheric Research 229, no. : 145-156.
One hydrochlorofluorocarbon and two hydrofluorocarbons (HCFC-22, HFC-125, and HFC-152a) were measured in air samples at the Cape Point observatory (CPT), South Africa, during 2017. These data represent the first such atmospheric measurements of these compounds from southwestern South Africa (SWSA). Baseline atmospheric growth rates were estimated to be 8.36, 4.10, and 0.71 ppt year-1 for HCFC-22, HFC-125, and HFC-152a, respectively. The CPT measurements were combined with an inverse model to investigate emissions from SWSA. For all three halocarbons, Cape Town was found to be the dominant source within SWSA. These estimates were extrapolated, based on population statistics, to estimate emissions for the whole of South Africa. We estimate South Africa's 2017 emissions to be 3.0 (1.6-4.4), 0.8 (0.5-1.2), and 1.1 (0.6-1.6) Gg year-1 for HCFC-22, HFC-125, and HFC-152a, respectively. For all three halocarbons, South Africa's contribution to global emissions is small (<2.5%), but future monitoring is needed to ensure South Africa's compliance with regulation set out by the Montreal Protocol and its Amendments.
Brett Kuyper; Daniel Say; Casper Labuschagne; Timothy Lesch; Warren R. Joubert; Damien Martin; Dickon Young; M. Anwar H. Khan; Matthew Rigby; Anita Ganesan; Mark Lunt; Colin O'dowd; Alistair J. Manning; Simon O'doherty; Michael Trevor Davies-Coleman; Dudley E. Shallcross. Atmospheric HCFC-22, HFC-125, and HFC-152a at Cape Point, South Africa. Environmental Science & Technology 2019, 53, 8967 -8975.
AMA StyleBrett Kuyper, Daniel Say, Casper Labuschagne, Timothy Lesch, Warren R. Joubert, Damien Martin, Dickon Young, M. Anwar H. Khan, Matthew Rigby, Anita Ganesan, Mark Lunt, Colin O'dowd, Alistair J. Manning, Simon O'doherty, Michael Trevor Davies-Coleman, Dudley E. Shallcross. Atmospheric HCFC-22, HFC-125, and HFC-152a at Cape Point, South Africa. Environmental Science & Technology. 2019; 53 (15):8967-8975.
Chicago/Turabian StyleBrett Kuyper; Daniel Say; Casper Labuschagne; Timothy Lesch; Warren R. Joubert; Damien Martin; Dickon Young; M. Anwar H. Khan; Matthew Rigby; Anita Ganesan; Mark Lunt; Colin O'dowd; Alistair J. Manning; Simon O'doherty; Michael Trevor Davies-Coleman; Dudley E. Shallcross. 2019. "Atmospheric HCFC-22, HFC-125, and HFC-152a at Cape Point, South Africa." Environmental Science & Technology 53, no. 15: 8967-8975.
This paper describes the development of a new sampling and measurement method to infer methane flux using proxy measurements of CO2 concentration and wind data recorded by Unmanned Aerial Systems (UAS). The flux method described and trialed here is appropriate to the spatial scale of landfill sites and analogous greenhouse gas emission hotspots, making it an important new method for low-cost and rapid case study quantification of fluxes from currently uncertain (but highly important) greenhouse gas sources. We present a case study using these UAS-based measurements to derive instantaneous methane fluxes from a test landfill site in the north of England using a mass balance model tailored for UAS sampling and co-emitted CO2 concentration as a methane-emission proxy. Methane flux (and flux uncertainty) during two trials on 27 November 2014 and 5 March 2015, were found to be 0.140 kg s−1 (±61% at 1σ), and 0.050 kg s−1 (±54% at 1σ), respectively. Uncertainty contributing to the flux was dominated by ambient variability in the background (inflow) concentration (>40%) and wind speed (>10%); with instrumental error contributing only ∼1–2%. The approach described represents an important advance concerning the challenging problem of greenhouse gas hotspot flux calculation, and offers transferability to a wide range of analogous environments. This new measurement solution could add to a toolkit of approaches to better validate source-specific greenhouse emissions inventories – an important new requirement of the UNFCCC COP21 (Paris) climate change agreement.
Grant Allen; Peter Hollingsworth; Khristopher Kabbabe; Joseph R. Pitt; Mohammed I. Mead; Samuel Illingworth; Gareth Roberts; Mark Bourn; Dudley E. Shallcross; Carl J. Percival. The development and trial of an unmanned aerial system for the measurement of methane flux from landfill and greenhouse gas emission hotspots. Waste Management 2019, 87, 883 -892.
AMA StyleGrant Allen, Peter Hollingsworth, Khristopher Kabbabe, Joseph R. Pitt, Mohammed I. Mead, Samuel Illingworth, Gareth Roberts, Mark Bourn, Dudley E. Shallcross, Carl J. Percival. The development and trial of an unmanned aerial system for the measurement of methane flux from landfill and greenhouse gas emission hotspots. Waste Management. 2019; 87 ():883-892.
Chicago/Turabian StyleGrant Allen; Peter Hollingsworth; Khristopher Kabbabe; Joseph R. Pitt; Mohammed I. Mead; Samuel Illingworth; Gareth Roberts; Mark Bourn; Dudley E. Shallcross; Carl J. Percival. 2019. "The development and trial of an unmanned aerial system for the measurement of methane flux from landfill and greenhouse gas emission hotspots." Waste Management 87, no. : 883-892.
Postgraduate scientists (here Chemists) can become isolated during their studies and will inevitably have times when their research seems to not be progressing. The Bristol ChemLabS public engagement programme provides many opportunities to ‘play’ and in so doing has had myriad benefits for these students. These include making friends with different postgraduate Chemists (particularly important when research groups are small), swapping ideas about research with groups that they would not normally meet, honing their science communication skills in both oral and written formats, re-energising their passion for science, getting away from the research laboratory and simply having fun.
Dudley Shallcross; Tim Harrison. Exploration: Public Engagement Activities for Chemistry Students. The Power of Play in Higher Education 2019, 145 -158.
AMA StyleDudley Shallcross, Tim Harrison. Exploration: Public Engagement Activities for Chemistry Students. The Power of Play in Higher Education. 2019; ():145-158.
Chicago/Turabian StyleDudley Shallcross; Tim Harrison. 2019. "Exploration: Public Engagement Activities for Chemistry Students." The Power of Play in Higher Education , no. : 145-158.
The significance of removal of atmospheric ammonia and amines by reaction with Criegee intermediates is assessed by kinetic studies.
Rabi Chhantyal-Pun; Robin J. Shannon; David P. Tew; Rebecca L. Caravan; Marta Duchi; Callum Wong; Aidan Ingham; Charlotte Feldman; Max R. McGillen; M. Anwar H. Khan; Ivan O. Antonov; Brandon Rotavera; Krupa Ramasesha; David L. Osborn; Craig A. Taatjes; Carl J. Percival; Dudley E. Shallcross; Andrew J. Orr-Ewing. Experimental and computational studies of Criegee intermediate reactions with NH3 and CH3NH2. Physical Chemistry Chemical Physics 2019, 21, 14042 -14052.
AMA StyleRabi Chhantyal-Pun, Robin J. Shannon, David P. Tew, Rebecca L. Caravan, Marta Duchi, Callum Wong, Aidan Ingham, Charlotte Feldman, Max R. McGillen, M. Anwar H. Khan, Ivan O. Antonov, Brandon Rotavera, Krupa Ramasesha, David L. Osborn, Craig A. Taatjes, Carl J. Percival, Dudley E. Shallcross, Andrew J. Orr-Ewing. Experimental and computational studies of Criegee intermediate reactions with NH3 and CH3NH2. Physical Chemistry Chemical Physics. 2019; 21 (26):14042-14052.
Chicago/Turabian StyleRabi Chhantyal-Pun; Robin J. Shannon; David P. Tew; Rebecca L. Caravan; Marta Duchi; Callum Wong; Aidan Ingham; Charlotte Feldman; Max R. McGillen; M. Anwar H. Khan; Ivan O. Antonov; Brandon Rotavera; Krupa Ramasesha; David L. Osborn; Craig A. Taatjes; Carl J. Percival; Dudley E. Shallcross; Andrew J. Orr-Ewing. 2019. "Experimental and computational studies of Criegee intermediate reactions with NH3 and CH3NH2." Physical Chemistry Chemical Physics 21, no. 26: 14042-14052.