1. New Particle Formation in the Global Atmosphere Fangqun Yu Atmospheric Sciences Research Center, State University of New York at Albany Zifa Wang Institute of Atmospheric Physics, Chinese Academy of Sciences Richard Turco Dept. of Atmospheric and Oceanic Sciences, University of California at Los Angeles

2. IPCC, 2007 Aerosol second indirect forcing ?? Nucleation CCN concentration

3. Nucleation and growth events Laakso et al., 2004

4. # of observed nucleation events RITS94 ACE1 INDOX99 Koponen02 Davison96 NAURU99 ACE-Asia ACE1 ACE2 NEAQS Surface-based observations of particle formation rates

5. H 2 SO 4 -H 2 O NH 3 Ternary Homogeneous Nucleation (THN) unimportant, at least in lower troposphere (Yu, JGR, 2006a, b) important, based on recent modeling study and measurements (Yu, ACP, 2006; Laakso et al., ACP, 2007) ????

6. In this study, the GEOS-3 grid with 2 o x2.5 o horizontal resolution and 30 vertical levels was used. Run the model from 07/2001-06/2002. J IMN = J ([H 2 SO 4 ], RH, T, Q, S 0 ) Nucleation rate look-up tables: To study global nucleation, we coupled a nucleation module with GEOS-CHEM.

7. Simulated annual mean nucleation rates averaged within the surface layer (0 – 150 m). Symbols are measured average local nucleation rate (typically over a window of several hours). Measurements over land are indicated by unfilled circles; circle size defines the number of nucleation events reported (refer to the lower scale), while color gives the average nucleation rate over the event ensemble.

8. Vertical structure of predicted annual-mean zonally-averaged nucleation rates calculated using GEOS-Chem coupled to an ion- mediated nucleation sub-model. Zonally-averaged latitudinal and vertical distribution of total ultrafine CN (> ~ 3-4 nm) aerosol concen- trations measured in situ during GLOBE, ACE-1, PEM-Tropics A and B, INTEX-A, and TRACE-P.

9. Ratio of annual mean IMN rates integrated within the lowest 3 km of atmosphere (the source strength due to IMN, #/cm 2 day) to the annual mean rate of emission of primary particles (source strength due to primary aerosol emission, #/cm 2 day).

10. J IMN = J ([H 2 SO 4 ], RH, T, Q, S 0 ) For each degree of surface warming, absolute RH could decrease 3%–5% in the upper troposphere and 3–10% in the middle troposphere (Minschwaner and Dessler, J. of Climate, 2004). Annual mean percentage change in nucleation rates (zonal average): (a) per degree of temperature increase, and (b) per 1% decrease in mean absolute RH. Aerosol generation over large regions of the atmosphere could decrease by 10–30% per degree of warming.

11. REDUCED nucleation & aerosol abundance LESS cooling due to aerosol radiative forcing WARMER atmosphere MORE greenhouse gases MORE heat trapped in the atmosphere Positive Nucleation Feedback = More Warming Positive nucleation feedback: Implications for global warming Decreased relative humidity

12. Summary 1.Formation and growth of ultrafine particles have been frequently observed in various locations. These particles may have important climatic and health effects. 2.We have studied new particle formation via ion-mediated nucleation in the global atmosphere by coupling nucleation module with GEOS-Chem. The spatial distributions of global IMN nucleation are consistent with existing measurements. IMN can lead to significant new particle formation in the global atmosphere. 3.We propose a positive climatic feedback mechanism involving nucleation and aerosol radiative forcing.

13. Future Research Long-term trend of particle nucleation in the global atmosphere Growth and evolution of nucleated particles in the global atmosphere, focusing on contribution of nucleated particles to the abundance of CCN Key parameters controlling nucleation and CCN abundance, and implications for climate feedback mechanisms (1) Positive nucleation-climate feedback (2) DMS-climate feedback (CLAW hypothesis) (3) Solar variation-aerosol-climate

14. Thank You!

15. Yu, JGR, 2002

16. T270RH65S1E7C2.5E7D2.5

17. Measurements of ions, charged clusters/particles, and total particles Air Ion Spectrometer (0.46-55 nm) Positiv e 6 nm 1 nm 3 nm Balance Scanning Mobility Analyzer (0.4-7 nm) Negati ve 1 nm 3 nm 6 nm From Laakso et al., 2005. From Vana et al., 2005.

18. From Hirsikko et al., 2007 Ions are involved in more than 90% of the particle formation days that can be clearly identified.

19. Laakso et al., 2006 Nucleated particles are overcharged in 90% of the particle formation days that can be clearly identified.

21. Pinker et al., Science, 2005