Since October 2003 I have been working as a researcher at the Royal Netherlands Meteorological Institute (KNMI) in the section of Chemistry and Klimate (CK). My principle responsibility is the development and valiadtion of the tropospheric version of the global chemistry transport model - TM5. My research interests concerns the investigation of the chemistry and physics of the atmosphere and the impact that human development and future climate change is having on it's composition.

I received my PhD in Atmospheric Chemistry from the University of Leeds in 1996 where my research was concerned with the study of free-radical reaction kinetics which occur in the aqueous phase (mimicking cloud droplets). The focus was iron catalysed reactions involved with acid rain generation. The technique was pulse radiolysis using the now defunct van-de-graaf accelerator housed at Cookridge Radiation Research Centre, which is now closed as a result of financial decisions taken by the University. After this I stayed at Leeds and spent a year performing flash photolysis studies of terpene reactions in solution (RINOXA2), followed by my first experience of using computers for chemical studies of the atmosphere (CAPRAM).

Within this project I had the opportunity to move to the Netherlands (University of Utrecht - IMAU) where I implemented a state-of-the-art aqueous phase chemical mechanism into a 1-D column model including both clouds and aerosols. From there I moved to AMOLF, Amsterdam where I spent a few years learning the techniques associated with retrieval of data products from earth-orbiting satellites(namely water vapour from GOME).Then I moved to the LSO laboratory at RIVM, the public health institute of the Netherlands, for work concerning the use of UV irradiance measurements and incident dose on the ground.

Finally, I moved to KNMI and shifted my focus back towards large-scale chemistry simulations. My main interests include the development and/or implementation of new parameterizations into global models for the description of physical processes such as the occurence of cirrus clouds and NAT particles, online photolysis, chemical mechanism development, large scale model validation and heterogeneous processes. I am currently also involved in performing decadel simulations of the recent past (2000-2009) to invectigate how changing emission patterns between the US, Europe, India and China are modifying the tropical troposphere and lifetimes of long-lived trace species (CO and CH4).

Stratospheric-Tropospheric version of TM5 Dec 2007 status

EU PROJECTS (Past and Present)

RINOXA-2 (no existing website)

CAPRAM

EDUCE (website defunct)

TOPOZ III

SCOUT-O3

GEMS

AMMA

QUANTIFY

GEOMON

Selected Publications

The Impact of Uncertainities in African Biomass Burning Emission Estimates on modeling Global Air Quality, Long Rage Transport and Tropospheric Chemical Lifetimes, J. E. Williams, M. van Weele, P. F. J. van Velthoven, M. P. Scheele, C. Liousse and G. R. van der Werf, Atmosphere, 3, 132-163, 2012

Future impact of non-land based traffic emissions in atmospheric ozone and OH - an optimistic scenario and a possible mitigation strategy, O. Hodenbrug, T. K. Berntsen, O. Dessens, M. Gauss, V. Grewe, I. S. A. Isaksen, B. Koffi, G. Myhre, D. Olivie, M. J. Prather, J. A. Pyle, F. Stordal, S. Szopa, Q. Tang, P. van Veltyhoven, J. E. Williams and K. Odemark, Atms. Chem. Phys, 11, 11293-11317, 2011

Uncertainty in the future distribution of tropospheric ozone over West Africa due to variability in anthropogenic emissions estimates between 2025 and 2050., J. E. Williams and P. F. J. van Velthoven, Int.J.Geophysics, Volume 2011, Article ID 324359, 10 pages, 2011

The West African Climate system: a review of the AMMA model inter-comparison initiatives, P. M. Ruti, J. E. Williams, F. Hourdin, F. Guichard, A. Boone, P. Van Velthoven, F. Favot, I. Musat, M. Rummukainen, M. Dominguez, M. A. Gaertner, J. P. Kafore, T. Losada, M. B. Rodriguez de Fonseca, J. Polcher, F. Giorgi, Y. Xue, I Bourar, K. Law, B. Josse, B. Barret, X. Yang, C. Mari and A. K. Traore, Atms. Sci. Letts., 12, 116-122, 2011.

Radiative forcing due to changes in ozone and methane caused by the transport sector, G. Myhre, K. P. Shine, G. Radel, M. Gauss, I. S. A. Isaksen, Q. Tang, M. J. Prather,J. E. Williams, P. van Velthoven, O. Dessens, B. Koffi, S. Szopa, P. Hoor, V. Grewe, J. Borken-Kleefeld, T. K. Berntsen and J. S. Fuglestvedt, Atmos. Environ., 45, 387-394, 2011

The influence of biomass burning and transport on tropospheric composition over the tropical Atlantic Ocean and Equatorial Africa during the West African monsoon in 2006, J. E. Williams, M. P. Scheele, P. F. J. van Velthoven, V. Thouret, M. Saunois, C. E. Reeves and J.-P. Cammas, Atmos. Chem. Phys.,10, 9797-9817, 2010

Impact of West African Monsoon convective transport and lightening NOx production upon the upper tropospheric composition: a multi-model study, B.Barret, J.E.Williams, I.Bouarar, X.Yang B. Josse, K. Law, M. Pham, E. Le Flochmoen, C. Liousse, V-H Peuch, G. D. Calver, J. A. Pyle, B. Sauvage ,P van Velthoven, H. Schlager, C. Mari and J.-P. Cammas, Atms. Chem. Phys.,10, 5719-5738, 2010

Global Chemistry simulations in the AMMA Multimodel Intercomparison Project, J.E.Williams, M.P.Scheele, P van Velthoven, I. Bouarar, K. Law, B. Josse, V-H Peuch, X Yang, J. Pyle, V. Thouret, B. Barret, C. Liousse, F. Hourdin, S. Szopa and A. Cozic, Bull.Am.Met.Soc., 611-624, 2010

The Influence of Biogenic Emissions from Africa on Tropical Tropospheric Ozone during 2006: a Global Modeling Study, J.E.Williams, M.P.Scheele, P.F.J.van Velthoven, J.-P.Cammas, V.Thouret, C.Galy-Lacaux, and A.Volz-Thomas,Atms.Chem.Phys, 9, 5729-5749, 2009

A modified band approach for the accurate calculation of online photolysis rates in stratospheric-tropospheric Chemistry Transport Models, J.E.Williams, J.Landgraf, A.Bregman and H.H.Walter, Atmos.Phys.Chem., 6, 4137-4161, 2006.

Implementing growth and sedimentation of NAT particles in a global Eulerian model, M.M.P.van den Broek, J.E.Williams and A.Bregman, Atmos.Phys.Chem., 4, 1869-1883, 2004.

Aqueous phase reaction of HNO4: The impact on tropopsheric chemistry, F.J.Dentener, J.E.Williams and S.Metzger, Journal of Atmospheric chemistry, 41(2), 109-133, 2002.

The influence of cloud chemistry on HOx and NOx in the moderately polluted Marine Boundary Layer : a 1-D modelling study. J.E.Williams, F.J.Dentener and A.R.van den Berg, Atmos.Chem.Phys., 2, 39-54, 2002.

The Reactivity of Biogenic Monoterpenes towards OH and SO4- radicals in de-oxygenated acidic solution, G.V.Buxton, G.A.Salmon and J.E.Williams, Journal of Atmospheric Chemistry, 36(2), 111-134, 2000.

The Reactivity of chlorine atoms in aqueous solution Part III : Reaction of Cl with solutes, G.V.Buxton,M.Bydder,G.A.Salmon and J.E.Williams, Phys.Chem.Chem.Phys.,2,237-245,2000.

A study of the spectra and reactivity of oxysulphur-radical anions involved in the chain oxidation of S(IV): a pulse and gamma-radiolysis study, G.V.Buxton, S.McGowan, G.A.Salmon, J.E.Williams and N.D.Wood, Atms.Environ., 30(14), 2483-2493, 1996.

Transition Metal Catalysed oxidation of SO2 in Clouds and Precipitation, J.E.Williams, PhD Thesis, 1996, University of Leeds

*****************************************************LATEST********************************************************

=================================JAN_2012==================================

The application of the Modified Band Approach for the calcuation of on-line photodissociation rates in TM5: implications for oxidative capacity

A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (J-values) has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA) including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species, the aerosol climatology which is adopted and the parameterizations adopted for improving the description of scattering and absorption by clouds. The resulting J-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in J -values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone (O3) changes by ±10% in the seasonal mean mixing ratios throughout the troposphere, especially over land. These changes and the perturbations in the photolysis rate of O3 induce changes of ±15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH4 by 5% and 4 %, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations. Geosci. Model. Dev.,5, 15-35, 2012.

The influence of methane variability on tropospheric NOx recycling

Presented at NCGG6, Amsterdam, The Netherlands, 2-4Nov, 2011

Effect of increasing Asian Emissions and meteorological variability on the composition of the UT/LS

Presented at the CARIBIC International Workshop, Seeheim, Germany, 4-6thOct, 2011

The sensitivity of Chemistry and Composition of the Troposphere on the Incident Solar Flux prescribed at the Top of the Atmosphere in a global CTM

Atmospheric composition, the oxidative capacity of the troposphere and resident chemical lifetimes of important trace gas species are essentially determined by the absolute rate of formation of free-radicals (e.g. OH) via fast photochemical reactions. Therefore an accurate estimate of the actinic flux with respect to altitude, location and season is a crucial step towards being able to capture the short- to medium-term fluctuations in chemical species typically seen by atmospheric observations. These variations are determined by solving the radiative transfer equation which is dependent on (e.g.) total overhead ozone, clouds, aerosols, etc as well as the incident solar flux at the top of the atmosphere (TOA). Here we use an optimized version of the '8-band' approach (Williams et al, 2006) in the global CTM TM5, which accounts for such dependencies in order to investigate the influence of different estimates for the incoming solar irradiance at TOA. For this purpose we utilize the recently compiled high resolution solar reference spectrum of Dobber et al (2008) that is currently used for retrievals from the Ozone Monitoring Instrument (OMI). We then compare against simulations which use a number of different solar spectra commonly used by the atmospheric science community. We subsequently quantify the sensitivity of global large-scale CTM calculations towards the choice of the TOA solar spectrum via comparisons against measurements and a detailed chemical budget analysis.

Poster presented at the 11th IGAC international meeting Halifax, Nova Scotia, 11-16th July, 2010.

Changes in the regional and global acidic deposition due to changes in anthropogenic emissions between 2000-2050

Poster presented at the Final QUANTIFY meeting in Munich, Germany 25-27th January, 2010.

Enhanced formation of HNO3 due to water vapour from the reaction of NO with HO2: The Effect on Tropospheric Composition.

Recent laboratory studies have shown that the direct formation of HNO3 may occur from the reaction of NO with HO2 (Butkovskaya et al, 2007), where 2D and 3D modeling studies have shown that including such a reaction has an important effect on tropospheric composition (Cariolle et al, 2008). Here it was concluded that the largest effects occurred in the mid to upper troposphere as a result of the temperature dependency. In this study we re-examine this reaction by introducing the effect of water vapour into the rate equation (Le Bras, Personal Communication, 2009) and subsequently apply it in the global CTM TM4, where the effect of water has been found to enhance the efficiency of the HNO3-forming channel by (e.g.) a factor of 8 at ~50% relative humidity (Butkovskaya et al, 2009). We show that including \ this catalytic effect of water vapour significantly increases the effects on the lifetimes of important trace gases such as CO, the availability of reactive nitrogen oxides (NOx) and tropospheric O3, especially in the tropical regions. By comparing the resulting gas phase distributions with measurements and the orginal formulation which neglects the water vapour enhancement we assess the degree to which including this catalytic effect alters the oxidative capacity of the atmosphere, the ability of the CTM to capture the tropospheric distribution of key species and the transport of trace gas species into the UTLS.

Presentations given at the Final SCOUT-O3 meeting in Schliersee, Germany 15-17th June, 2009.

For copies of papers not freely available on the web please send me a mail.

Full publication list