Processes Controlling Arctic Aerosol Number and Size: Seabird-Climate Connections B. Croft1, R. V. Martin1,2, G. R. Wentworth3, W. R. Leaitch4, J. G. Murphy3, J. Kodros5, P. Tunved6, T. J. Breider7, S. D. D’Andrea5, J. P. D. Abbatt3 and J. R. Pierce5,1 1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada 2Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA 3Science and Technology Branch, Environment Canada, Toronto, ON, Canada 4Department of Chemistry, University of Toronto, Toronto, ON, Canada 5Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA 6Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden 7School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA NETCARE 2015 Workshop University of Toronto, Toronto, Canada November 16, 2015

Strong Seasonal Cycle in Aerosol Number and Size at High-Arctic Sites ___ Data from 2011-2013 Alert, Nunavut, Canada: SMPS Zeppelin, Svalbard, Norway: DMPS Alert ___ Zeppelin dN/dlogDp [cm-3] dN/dlogDp [cm-3] dN/dlogDp [cm-3] Alert Zeppelin What are the controlling processes? 20 50 100 500 20 50 100 500 20 50 100 500 20 50 100 500 Dp [nm] Dp [nm] ] Dp [nm] ] Dp [nm]

Observed Seasonal Mean Aerosol Size Distributions Alert, Nunavut, Canada

GEOS-Chem-TOMAS Model is Used to Interpret the Observed Cycle Alert, Nunavut, Canada

Key Processes: Wet Removal Alert, Nunavut, Canada Wet removal reduces summertime accumulation mode

Key Processes: Wet Removal, Coagulation Alert, Nunavut, Canada Interstitial coagulation in clouds reduces non-summer Aitken mode Wet removal reduces summertime accumulation mode

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

Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Nucleation Dp < 10 nm Aitken 10 < Dp < 100 nm Accumulation Dp > 1000 nm Coarse Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG 100 < Dp < 1000 nm

Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Nucleation Dp < 10 nm Aitken 10 < Dp < 100 nm New-Particle Formation Coagulation Accumulation Dp > 1000 nm Coarse Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG 100 < Dp < 1000 nm

Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Nucleation Dp < 10 nm Aitken 10 < Dp < 100 nm New-Particle Formation Transport Coagulation Accumulation Dp > 1000 nm Coarse Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG 100 < Dp < 1000 nm

Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Nucleation Dp < 10 nm Aitken 10 < Dp < 100 nm New-Particle Formation Transport Coagulation Accumulation Dp > 1000 nm Coarse Condensation and Transport Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG Wet removal by precipitation

Seasonal Cycles of Number Process Rates for Entire Arctic Troposphere Nucleation Dp < 10 nm Aitken 10 < Dp < 100 nm New-Particle Formation Transport Coagulation Transport and Emissions Accumulation Coarse Condensation and Transport Number budgets for GEOS-Chem-TOMAS simulation NEWSCAV+COAG Dp > 1000 nm Wet removal by precipitation

Particle Precursors: Arctic Seabirds Emit Ammonia of ~ 50 Gg yr-1 1. Gas production Guano + H2O + O2 --> NH3(g) 2. Particle production NH3(g) + H2SO4(g) + H2O(g) --> new particles Circles: Riddick et al., 2012 inventory Stars: Added emissions from Circumpolar Seabird Data Portal [Mg NH3 yr-1 colony-1]

Seabird Colony Emissions Strongly Control Free NH3 In Arctic Change in Summertime Mean Surface Layer NH3(g)+NH4+(s) With Seabird Colony NH3 Emissions in GEOS-Chem-TOMAS Model Climate relevant impacts Increased new-particle formation More numerous cloud condensation nuclei following particle growth Clouds with greater reflectivity of solar radiation [%] 0 50 100 150 200 250 300 350 400 450 500

Sufficient NH3 to Simulate Bursts of New-Particle Formation at Alert Aerosol Number with Dp > 10 nm from CPC

Seabird Colony NH3 Sufficient to Control Alert Aerosol Neutralization

New Particles Grow to Sizes that Change Cloud Droplet Number

Pan-Arctic Aerosol Indirect Effect from Seabird Colony NH3: -0.3 Wm-2 For same liquid water content, clouds with more and smaller cloud droplets are brighter --> cooling.

Summary and Outlook Thanks! Questions ?? Pan-Arctic aerosol number and size have a strong seasonal cycle. Key processes in Arctic summer: more efficient wet removal, ongoing northward transport, accumulation mode number erodes, promotes new-particle formation. GEOS-Chem-TOMAS indicates that Arctic seabird NH3 emissions yield sufficient free NH3 to key trigger to new-particle formation. Growth of the seabird-influenced particles modifies Arctic cloud droplet number, yielding pan-Arctic aerosol indirect effect of -0.3 W m-2. Future work: evaluate GEOS-Chem-TOMAS vertical profiles of aerosol number, CCN, IN and related-process representations with NETCARE measurements. Thanks! Questions ??

Extra Slides

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

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

Effective Diameter Seasonal Cycle Occurs Throughout the Arctic DJF MAM GEOS-Chem-TOMAS simulation NEWSCAV+COAG Stars: Measurement values Surface Layer Effective Diameter [nm] JJA SON Alert Zeppelin

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

Wet Removal Efficiency Has Stronger Seasonal Cycle in Polar Regions More efficient wet removal => shorter number lifetimes at altitude of Arctic haze layer (1.5-4 km) during spring to summer transition. Spring-summer change in wet deposition lifetime is stronger than transport change. GEOS-Chem simulation NEWSCAV+COAG

Zeppelin, Svalbard

Zeppelin, Svalbard

Alert

North of 78N

North of 50N

Global