Indian Institute of Technology Kanpur, India. First European Space Weather Week, ESTEC, Noordwijk, (The Netherlands), 29 th November-3 rd December Model Studies on atmospheric ion-induced nucleation of sulfuric acid and water: Interpretation of in-situ measurements Vijay Kanawade, Sanjeev Kumar and S. N. Tripathi Department of Civil Engineering, Indian Institute of Technology Kanpur, India Motivation  To develop an efficient and fast ion induced nucleation model, which will be implemented in a global model to study nucleation of particle on global scale.  To interpret observed atmospheric nucleation events and to understand the role of cosmic ray induced ionization on particle microphysics. Introduction  Particle nucleation has been observed in atmosphere that has not been explained by Homogenous Nucleation theory  Ion-induced nucleation is shown to be an effective pathway for explaining new particle formation in the UTLS region (Lee et al., 2003). Ions are formed by Galactic Cosmic Rays (GCRs) at the rate of ion pairs (Q) cm -3.s -1 in the background lower atmosphere.  Several factors favouring ion-induced nucleation exist in the UTLS region including high sulfuric acid concentration (H 2 SO 4 ), low temperatures (T), relatively low surface area (SA) of preexisting aerosols, and sufficient sun exposure. Model  Ion induced nucleation parameterization based on Kinetic model (SAWNUC) (Lovejoy et al., 2004) is implemented in the H 2 SO 4 -H 2 O Aerosol Microphysical model (SAMIN) (Tripathi et al., 2004).  Nucleation parameterization is valid in the ranges: 200≤T≤280K, 5≤Relative Humidity(RH)≤95%, 10 5 ≤H 2 SO 4 ≤10 8 molecules.cm -3, 2 ≤SA≤200µm 2.cm -3, and 2≤Q≤30 ion pairs cm -3.s -1.  Besides ion induced nucleation (IIN), SAMIN simulates H 2 SO 4 condensational growth, water vapour equilibrium, particle-particle coagulation and sedimentation.  The particle size range in the SAMIN model covers particles having radii between 0.3 nm to 1.0 µm. The size range is geometrically divided into 40 bins and integration time step used is 60 seconds. SAMIN and SAWNUC predicted aerosol size distributions for the enviormental codition T=236K, RH=4%, SA=15 µm 2.cm -3, Q=12 ion pairs cm -3.s -1 for different H 2 SO 4 gas concentration is presented in Figure 1(a,b,c). It can be seen that SAMIN and SAWNUC predicted aerosol size distributions are in good agreement. Figure 1(a,b,c). Comparison between SAMIIN model and SAWNUC model predicted aerosol size distribution for different sulfuric acid gas cocnetrations. Model Predictions Evolution of the size distribution of particle predicted by the model for a typical environmental condition within UTLS region is plotted in the Fig. 2(a,b). Figure 2(a) shows the particle growth from 3 nm to 100 nm for 40 hr. model run. Figure 2(b) depicts the evolution of size distribution for radius range from 0.3 nm to 100 nm over a 24 hr. period. The model run was from sun rise until sunset to predict size distribution of aerosol particles. Figure 2.(a,b): SAMIN predicted particle size distribution curve and particle production for environmental condition within UTLS region. Interpretation of Observed Nucleation Events SAMIN was run using measured environmental parameters e.g. T, RH, H 2 SO 4, SO 2 (Sulfur dioxide, pptv), OH, to interpret different observed atmospheric nucleation events viz., (i) TOPSE (Tropospheric Ozone Production about the Spring Equinox), (ii) ACE-1 (First Aerosol Characterization Experiment-One), (iii) PEM Tropics A (Pacific Exploratory Mission in the Tropics-Phase A), (iv) PEM Tropics B (Pacific Exploratory Mission in the Tropics-Phase B), (v) TRACE P (TRAnsport and Chemical Evolution over Pacific) TOPSE (Tropospheric Ozone Production about the Spring Equinox) Table 1 summarizes the observed environmental parameters during TOPSE experiment, where in-situ new particle production were observed. We have calculated new particle production (3-4nm, 3-8nm) for the observed environmental parameters, by running the model from sunrise until the observation time (see Table 1). The direct comparison between the model predicted and observed Ultra fine Condensation Nuclei (UCN)>3nm is problematic because the history of the air parcel containing the fresh ultra fine particles as well as aged particles is uncertain and also temperature and relative humidity is changing along the path of air parcel. To interpret UCN >3nm, we have computed back trajectory of the air parcel using HYSPLIT model for TOPSE flight 16 observed environmental parameters (Figure 3(a)) and SAMIN model run for 2 days with these HYSPLIT calculated T and RH to interpret on UCN>3nm. Table 1: Observed and Model predicted particle concentrations for TOPSE Experiment Flight/ location Local Time Alt. km Temp. K RH % P (press.) mb T[H 2 SO 4 ] 10 6 cm -3 SAQ Max. Observed particle Model Predicted particle number conc. cm -3 number Conc. cm nm 3-8nm >3nm 3-4nm 3-8nm >3nm Flight (within SO Plume) Flight ( Above Plume) Figure 3(a)Figure 3(b) Figure 3(c) Figure 3. (a) 2-day Back Trajectory plot for air parcel height, T and RH during TOPSE experiment. (b) Comparison between observed and model predicted UCN>3nm for the observed environmental parameters during TOPSE experiment. (c) Sensitivity test for preexisting particle surface area on ultra fine particle (3-4nm) during TOPSE experiment. Figure 4. (a) Comparison between observed and model predicted ultra fine particle (3-4nm) for PEMT A experiment flight 10. (b) Comparison between observed and model predicted UCN>3nm for PEMT A experiment. flight 10. (c) Comparison between observed and model predicted ultra fine particle (3-10nm) for ACE 1 experiment. Flight 17. T[H 2 SO 4 ]= Observed H 2 SO 4 plus Calculated H 2 SO 4 ;(H 2 SO 4 calculated with the observed SO 2 and OH concentration by using rate limiting reaction OH + SO 2 = H 2 SO 4 (DeMore et al., 1997)) Figure 4(a)Figure 4(b) Figure 4(c) Conclusion:  It was found that SAMIN predicted ultra fine particle (3-4nm,3-8nm,3-10nm) number concentrations are in good agreement with the observed one during different nucleation events in the middle and upper troposphere. Also UCN>3nm number concentration is also matching quite well with the observed one during TOPSE experiment.  We conclude that ion induced nucleation play key role in the formation of ultra fine particles in the cold middle and upper troposphere (~4-7km) for a range of parameters T= K, RH=4- 66%, H 2 SO 4 =2   10 7 molecules.cm-3, SA=2-200μm 2.cm -3 and Q=2-30 ion pairs cm -3.s -1, for which SAMIN is able to predict observed new particle formation. Acknowledgment This work has been supported through a research grant of ISRO-RESPOND programme of Indian Space Research Organization. We thankfully acknowledge the encouragement and support received from the Director, IIT Knapur. We also acknowledge Data Manger, RAF, NCAR for data provided for the purpose of analysis and validation and their continuous help during study. References:\ 1.DeMore, W. B., S.P.Sandar, D.M.Golden,R.P.Hampson,M.J.Kurylo,C.J.Howard,A.R.Ravishankar,C.E.Kolb, and Molina, Chemical kinetics and photochemical data for use in stratospheric mo0deling, JPL Publ.,97-4, Modgil, M. S., Kumar, S., Tripathi, S. N., and E.R. Lovejoy, A Parameterization of Ion Induced Nucleation of Sulphuric Acid and Water for Atmospheric Conditions, Under reviewJ. Geophys. Res. 3.Lee,S..H., J.M. Reeves, J.C. Wilson, D.E. Hunton, A.A. Viggiano, T.M. Miller, J. O. Ballenthin, and L.R. Lait, Particle formation by ion nucleation in the upper troposphere and lower stratospheer, Science, 301, Lovejoy, E. R., J. Curtius, and K. D. Froyd, Atmospheric ion-induced nucleation of sulfuric acid and water, J. Geophys. Res., Vol. 109, No. D8, D08204, /2003JD004460, Tripathi, S. N., X. P. Vancassel, R. G. Grainger, and H. L. Rogers, A Fast Stratospheric Aerosol Microphysical Model (SAMM): H 2 SO 4 -H 2 O Aerosol Development and Validation, AOPP Memorandum , Department of Physics, University of Oxford, Table 2: Observed and model predicted particle number concentration for atmospheric Nucleation events Flight/ location Local Time Alt. km Temp. K RH % P mb T[H 2 SO 4 ] 10 6 cm -3 SAQMax. Obs. Particle Model Predicted particle conc. cm -3 Particle conc. cm nm 3-9nm Flight Flight/ location Local Time Alt. km Temp. K RH % P (press.) mb T[H 2 SO 4 ] 10 6 cm -3 SAQMax. Obs. Particle Model Predicted Particle Conc. cm -3 Particle Conc. cm nm 3-10nm Flight Flight Flight ACE 1 (First Aerosol Characterization Experiment-one) PEM Tropics A (Pacific Exploratory Mission in the Tropics-Phase A) (a)(c)(b) PEM Tropics B (Pacific Exploratory Mission in the Tropics-Phase B) Flight/ location Local Time Alt km Temp deg.K RH % P mb T[H 2 SO 4 ] 10 6 cm -3 SA a QbQb Max. Obs. Particle Model Predicted Particle Conc. cm -3 Particle Conc. cm nm 3-10nm 3-4nm 3-10nm Flight (a) (b). Future Work  Present aerosol microphysical model is being modified to study the effect of ions on particle formation, which activates into cloud condensation nuclei and to study cloud microphysics.