1. Processes Controlling the Seasonal Cycle of Arctic Aerosol Number and Size B. Croft 1, R. V. Martin 1,2, W. R. Leaitch 3, P. Tunved 4, T. J. Breider 5, S. D. D’Andrea 6, and J. R. Pierce 6,1 1 Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada 2 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA 3 Science and Technology Branch, Environment Canada, Toronto, ON, Canada 4 Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden 5 School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA 6 Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA AAAR 34 th Annual Conference, Minneapolis, Minnesota Session 1.RA Remote and Regional Aerosols I October 13, 2015

2. Strong Seasonal Cycle in Aerosol Number and Size at High-Arctic Sites 20 50 100 500 20 50 100 500 20 50 100 500 20 50 100 500 D p [nm] D p [nm] ] D p [nm] ] D p [nm] dN/dlogD p [cm -3 ] dN/dlogD p [cm -3 ] dN/dlogD p [cm -3 ] Data from 2011-2013 Alert, Nunavut, Canada: SMPS Zeppelin, Svalbard, Norway: DMPS Alert Zeppelin ___ Alert Zeppelin

3. Effective diameter [nm] 300 280 260 240 220 200 180 140 120 300 250 200 150 100 50 0 Total Number Concentration [cm -3 ] J F M A M J J A S O N D Alert and Zeppelin Are Similar Despite Their Geographic Separation Total number maxima in spring and summer Effective diameter minima in summer Q. What processes control these seasonal cycles?

4. Alert GEOS-Chem-TOMAS Model is Used to Interpret the Observed Cycle Alert, Nunavut, Canada GEOS-Chem-TOMAS with ternary nucleation scheme Alert, Nunavut, Canada

5. Alert GEOS-Chem-TOMAS Model is Used to Interpret the Observed Cycle Alert, Nunavut, Canada GEOS-Chem-TOMAS with ternary nucleation scheme Alert, Nunavut, Canada

6. Alert GEOS-Chem-TOMAS Model is Used to Interpret the Observed Cycle Alert, Nunavut, Canada GEOS-Chem-TOMAS with ternary nucleation scheme Alert, Nunavut, Canada

7. Alert GEOS-Chem-TOMAS Model is Used to Interpret the Observed Cycle Alert, Nunavut, Canada GEOS-Chem-TOMAS with ternary nucleation scheme Alert, Nunavut, Canada

8. Alert GEOS-Chem-TOMAS Model is Used to Interpret the Observed Cycle Alert, Nunavut, Canada GEOS-Chem-TOMAS with ternary nucleation scheme Alert, Nunavut, Canada

9. Key Processes: Wet Removal, Coagulation and New-particle Formation Alert, Nunavut, Canada

10. Key Processes: Wet Removal, Coagulation and New-particle Formation Alert, Nunavut, Canada

11. Key Processes: Wet Removal, Coagulation and New-particle Formation Alert, Nunavut, Canada Wet removal reduces summertime accumulation mode

12. Key Processes: Wet Removal, Coagulation and New-particle Formation Alert, Nunavut, Canada Interstitial coagulation in clouds reduces non- summer Aitken mode Wet removal reduces summertime accumulation mode

13. Interstitial coagulation in clouds reduces non- summer Aitken mode Key Processes: Wet Removal, Coagulation and New-particle Formation Alert, Nunavut, Canada

14. Effective Diameter Seasonal Cycle Occurs Throughout the Arctic GEOS-Chem-TOMAS simulation NEWSCAV+COAG Stars: Measurement values Alert Zeppelin Effective Diameter [nm] Surface Layer DJFMAM JJASON

15. Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG Nucleation Accumulation Aitken Coarse

16. Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG Coagulation New-Particle Formation Nucleation Accumulation Aitken Coarse

17. Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG Transport Coagulation New-Particle Formation Nucleation Accumulation Aitken Coarse

18. Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG Transport Coagulation Condensation and Transport Wet removal by precipitation New-Particle Formation Nucleation Accumulation Aitken Coarse

19. Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG Transport Coagulation Condensation and Transport Wet removal by precipitation Transport and Emissions New-Particle Formation Nucleation Accumulation Aitken Coarse

20. In Summertime Transport Diminishes, Yet Has Non-Negligible Role GEOS-Chem-TOMAS simulation NEWSCAV+COAG Transport weakens in spring to summer transition Nucleation Size (D p < 10 nm) Aitken Size (10 nm < D p < 100 nm) Accumulation (0.1 μm <D p < 1 μm ) Coarse Size (D p > 1 μm )

21. Wet Removal Efficiency Has Stronger Seasonal Cycle in Polar Regions Spring => Summer: More efficient wet removal reduces lifetime at 1.5-4 km, altitude of Arctic haze layer GEOS-Chem simulation NEWSCAV+COAG Spring-summer change in wet deposition lifetime is stronger than transport change. North of 78 °NNorth of 66 °NNorth of 50 °N Global

22. Summary and Outlook Arctic aerosol number and size => strong, similar seasonal cycle at Alert, Nunavut and Zeppelin, Svalbard. Total number maxima: spring (Accumulation mode) and summer (Aitken mode). Effective diameter minimum: summer (180 nm), maximum: winter (260 nm). GEOS-Chem-TOMAS => Arctic summer: more efficient wet removal, ongoing northward transport, accumulation mode number erodes, promotes new-particle formation. Coagulation in clouds reduces Aitken number in non-summer. Summertime Arctic aerosol controlled by natural, regional emissions, which have poorly understood effects related to clouds and climate (Poster 8CC.2, Aerosols, Clouds, & Climate, Thursday PM). Thanks! Questions ??

23. Extra Slides

24. Zeppelin, Svalbard

26. Alert

27. North of 78N

28. North of 50N

29. Global