Atmospheric Global Model Simulations of Sulfate Aerosols
by
Sunita Verma
Centre for Atmospheric Sciences
Submitted
in fulfillment of the requirements of the degree of
Doctor of Philosophy
to the
Indian Institute of Technology Delhi
June 2005
77'1
SLIVIS - 1-')13
Vree-A
CERTIFICATE
This is to certify that the thesis entitled "Atmospheric Global Model Simulations of Sulfate Aerosols" being submitted by Sunita Verma for the award of the degree of DOCTOR OF PHILOSOPHY, is a record of original bona fide research work carried out by her. She has worked under our joint guidance and supervision and has fulfilled the requirements for the submission of this thesis. The results presented in this thesis have not been submitted in part or full to any other University or Institute for the award of any degree or diploma.
(Dr. 0. P. Sharma)
Professor Senior Scientific Officer - I
Centre for Atmospheric Sciences Centre for Atmospheric Sciences Indian Institute of Technology Delhi Indian Institute of Technology Delhi New Delhi - 110 016, India New Delhi - 110 016, India
Acknowledgements
I express my deep sense of gratitude to my supervisors Prof. 0. P. Sharma and Dr. H. C. Upadhyaya, for their effort, painstaking guidance, support and constant en- couragement throughout the research work. Their insistence on simplicity, clarity and completeness of the expression together with the quality of work had a major role in tak- ing this thesis to the final form.
1 am deeply indebted to Prof. 0. P. Sharma for his intense involvement effort and patience during the development work. His deep insight into problems, imaginative ideas has always been a constant source of inspiration and motivation for me.
My sincerest thanks to Dr. Olivier Boucher of LOA (France) for his valuable guid- ance, throughout involvement effort and suggestions, which has been invaluable for me, for the thesis to take the final shape. I wish to express my highest appreciation to Dr. M.
Shekar Reddy (post-doc, GFDL, NOAA, U.S.A.) for providing me access to data on the Indian emissions and also helping me at several stages of the work.
I thank all the faculty members of Centre for Atmospheric Sciences (CAS), for being so helpful and supportive. I would also like to thank the CAS staff- Mrs. Asha Narula, Narendra Kumar and K. K. Sharma, to name a few, for extending help during this work.
My sincere thanks to my colleague, Sanjib Kumar Deb for taking time out from his Ph.D. work, to help me with the experimental and analysis work at several times. It has been pleasure to spent some very relaxing and light moments with Swagata, Neeru,
Rashmi, Anumeha, Sankalp, Lalit and Senthil in my otherwise very tiring schedule. I would like to thank Sunandanlahri for taking time out and helping me in printing the the- sis.
I cannot begin to thank my parents and my brothers, who were always there by my side, for any help that I needed and finally, I thank my friend circle (Nidhi, Rekha, Tony, Nishi, Shilpi and others) for being there for me always...
I am grateful to Indo-French Centre for the Promotion of Advanced Research / Centre Franco-Indien Pour la Recherche Avancee for the financial support in the form of a schol- arship to pursue Ph.D. programme at IIT, Delhi and giving me opportunity to work with
Dr. Olivier Boucher at LOA, France for three months under project entitled "Aerosols and Indian Monsoons" (1911-2). During my visit to France the computational support by Institut du Developpement et des Resources en Informatique Scientifique (IDRIS) of CNRS (France) was provided under project 031167.
(Sunita Verma)
ABSTRACT
The Indian Ocean Experiment (INDOEX) emphasized efforts for advancing the de- velopment of global chemistry models, including refinements to chemical/physical pa- rameterizations and improving the numerical schemes. This thesis is much in line with this philosophy of INDOEX. The primary goal of this thesis is, therefore, to develop a three dimensional interactive chemistry module and couple it subsequently with atmo- spheric general circulation model (AGCM) in order to study the response of aerosols to atmospheric forcing. First, the development of such a chemistry-AGCM has been ac- complished following basic reaction mechanisms that describe the dynamics of sulfate aerosols faithfully, and then several numerical simulations have been carried out using emission fields and various forcings (both idealized and real) in order to evaluate the model capability to reproduce the sulfate aerosols distribution and evolution. There is, however, a question of resolution and inclusion of sophisticated parameterizations to rep- resent complex chemical and physical processes that occur at scales much smaller than the model resolution.
A number of studies have been conceived and subsequently completed using the AGCM of Labratoire de Meteorologie Dynamique, referred in the text as LMDZ. With the help of some innovative symmetric experiments, during all stages of this development, many types of errors, either in the coding of the numerical schemes or the specification of inclusion of tracers or any inconsistency in the choice of parameters, were successfully detected and were then eliminated. Thus, it has been a great experience and learning but all cannot be described for the reasons of brevity and conciseness of the presentation. The unique aspects of the interactive chemistry module employed in the present thesis are the following:
(i) The most significant original contribution is running the chemistry and transport/dynamics fully interactively. This has been a major shortcoming of many very good prior models.
In contrast to offline model approach, it uses a complete online approach to simulate dis- tribution of sulphur compounds i.e. the sulphur chemistry is calculated directly within the LMDZ that allows for complex interaction between chemistry and dynamical processes for investigating the role of sulfate aerosols on climate system.
(ii) A comprehensive numerical scheme has been implemented to deal with the gas-phase and aqueous-phase reactions in a AGCM, where the concentrations of radicals like OH, H02 and gases like 03, 1-1202, NH3 and NOx are computed within the zoom version of LMD.
(iii) In most of the global sulphur models only sulfate mass is estimated as a prognostic variable. The number concentration is inferred assuming a constant size distribution. In contrast, in our implementation the sulfate number concentration is also treated as a prog- nostic variable. The knowledge of the sulfate aerosol number concentration is important to understand the indirect radiative forcing of the aerosols and to refine estimates of the direct radiative forcing.
(iv) In particular, the model considers an interactive scheme for feedback from chemistry to meteorology with internally resolving microphysical properties of aerosols for radia- tive transfer computations. Thus, it is a step towards correcting the deficiencies where the microphysics and feedbacks are run off-line to calculate the indirect effect of aerosols.
This is, possibly, for the first time that such an attempt from ab-initio level has been
made in India. This new approach (interactive) in numerical chemistry modelling is quite versatile in studying atmospheric chemistry phenomena over an area of interest (e.g. a limited region). There has been focus on the demonstration of the performance of the model and its assessment by employing appropriate forcing from the outputs of a gen- eral circulation model (GCM). Hence, the model was forced, in some of the experiments, with the emission fields derived mostly from GEIA inventory, and forcing (wind and ther- modynamic) derived from the ECMWF Analyses. The simulations put in evidence the satisfactory performance of this chemistry-AGCM. From the analyses of numerical exper-
iments, the interactive chemistry-AGCM appears to be a useful tool for sulfate aerosols simulations in view of the following findings
1. Model simulates well the broad patterns of observations on the surface mass and number concentration, vertical profiles, and mass transport of sulfate aerosols dur- ing winter and summer seasons.
2. The sulfate aerosol distribution for INDOEX-IFP has been simulated using this model. This work investigated the links between the sulfate aerosols and its trans- port to oceanic regions by using GCM. This study also explained the role of winter monsoon winds in advecting sulfate aerosols to nearby regions. The contribution of Indian emissions to these advected plume over the Indian Ocean and India has also been evaluated,
3. Carrying forward the model skills in representing the optical properties over the INDOEX region, the direct and indirect forcing of sulfate aerosols are estimated on the global scale. As the prediction of CDNC depends upon the concentration of sulfate aerosol and varies with the implified cloud properties, the model design internally resolves the cloud droplet number concentration (CDNC) to the changes
in the forcing.
4. One of the main conclusions of this thesis is that the Indian emissions are not the sole cause for the high sulfate and AOD concentrations over the Indian Ocean dur- ing winter. The Indian contribution is more than 60% over India and 30-50% over the Arabian Sea.
5. The magnitude of the global annual mean direct effect estimated by the model is - 0.48 W m-2, and that of the indirect effect is -0.71 W m-2. The estimates of sulfate aerosol forcing lie in the range of estimate (-0.26 to -0.81 W m-2).
However, the final conclusions can only be derived after a very ambitious programme of intense numerical experimentation and comparison of its simulations with those of other models. This is now feasible as there are international programmes for the evalu- ation of chemistry transport models (CTMs) where the models are required to produce simulations from identical initial and boundary conditions. This is an important activity for the future development and evolution of the model.
One of the main aims of this ab-initio development of chemistry-AGCM is to have multi-component approach. Evidently, in addition to sulfate aerosol, the other aerosol constituents (dust, soot etc.) which could have an important bearing on the climate and its variability are needed to be included. It is planned, as part of the future developments, to design a chemistry module which will include all important aerosol constituents. An- other possibility will however be explored by performing sensitivity studies experiments particularly over the Indian Ocean and study the response of sulfate aerosol distribution, its subsequent movement and transport etc. in respect to summer monsoon.
Contents
List of Figures (i)
List of Tables (vii)
List of Acronyms (viii)
1 Introduction 1
1.1 Introduction 1
1.2 Aerosols and their sources 2
1.3 Aerosol classifications 3
1.4 Aerosol distribution 5
1.5 Aerosol-climate interaction 7
1.5.1 Direct effect 7
1.5.2 Indirect effect 8
1.6 Sulfate aerosols 10
1.7 Objectives and organisation of the thesis 12
2 Model Description 17
2.1 Introduction 17
2.2 Atmospheric general circulation model 19
2.2.1 Dynamics 21
2.2.1.1 Time integration 23
2.2.1.2 Matsuno leap-frog scheme 24
2.2.2 Physics 25
2.2.2.1 Convective transport 26 2.2.2.2 Aerosol optical and radiative properties 28
2.2.2.3 Direct effect 29
2.2.2.4 Indirect effect 31
2.2.3 Chemistry and aerosol module 32 2.2.3.1 Gas-phase chemistry 34 2.2.3.2 Aqueous-phase chemistry 40
2.2.3.3 Aerosol module 45
2.2.4 Initialisation 52
2.2.5 Dry and wet deposition 52
3 Simulation of Sulphur Cycle 57
3.1 Introduction 57
3.1.1 Sulphur cycle and estimation of mass balance 58
3.2 Design of experiments 59
3.2.1 Emissions 59
3.2.2 Numerical simulations 60
3.3 Evaluation of model results 60 3.3.1 Global surface and zonal distributions 60 3.3.1.1 The hydroxyl radical (OH) 63 3.3.1.2 Hydrogen peroxide 66
3.3.1.3 Ozone 66
3.3.1.4 Dimethyl sulphide 68 3.3.1.5 Methanesulphonic acid 71
3.3.1.6 Sulphur dioxide 72
3.3.1.7 Sulfate mass concentrations 73 3.3.1.8 Sulfate number concentrations 76 3.4 Sulphur species at continental/polluted areas 77 3.5 Vertical distribution of sulphur species 79
3.5.1 Dimethyl sulphide 81
3.5.2 Sulphur dioxide 82
3.5.3 Sulfate 82
3.5.4 Hydrogen peroxide 82
3.6 Lifetimes of sulphur species 88
3.7 Discussion and conclusions 92
4 Numerical Simulations for INDOEX Region 95
4.1 Introduction 95
4.2 Design of experiments 97
4.2.1 Emissions 97
4.2.2 Numerical simulations 98
4.3 Results 99
4.3.1 Model evaluation 99
4.3.1.1 The Kaashidhoo Climate Observatory 99 4.3.1.2 Sulfate mass concentration and AOD at KCO . . . . 100 4.3.1.3 Sulfate number concentration 101 4.3.2 Latitudinal variations 103 4.3.2.1 Sulfate aerosol number concentration 103
4.3.2.2 Sulfate AOD 107 4.3.3 Regional distribution for INDOEX-IFP 109 4.3.3.1 SO2 concentration 109 4.3.3.2 Sulfate mass and number concentrations 109 4.3.3.3 Sulfate AOD and its radiative properties 111 4.3.4 Indian source contribution to sulfate burden 113
4.4 Conclusions 114
5 Optical and Radiative Properties of Sulfate Aerosols 116
5.1 Introduction 116
5.2 Optical properties and radiative forcing 116
5.3 Design of experiments 117
5.3.1 Emissions 117
5.3.1.1 Present day simulations 118 5.3.1.2 Pre-industrial simulations 118 5.3.2 Numerical simulations 118
5.4 Results 119
5.5 Conclusions 127
6 Conclusions and Scope for Future Work 129
6.1 Concluding remarks 129
6.2 Scope for future work 133
6.2.1 Refinement of the model (chemistry-AGCM) 133 6.2.2 Inclusion of missing pathways 134
6.2.3 Sensitivity studies 134
6.2.4 Further developments: a multi-component approach 135
6.2.5 Linking aerosols and the Indian monsoon 135
Bibliography 137
Appendix I
Brief bio-data of the author
