Theme 1: Carbonaceous Aerosol (EC and OC) Theme Leader: Abbatt, UofT (POLAR6, Amundsen, Alert, snow measurements); Co-Leader: Leaitch, EC (POLAR6,Whistler, Alert measurements, optical properties) Co-investigators: Bertram, UBC (Whistler, Alert measurements), Evans, UofT (snow measurements, source-receptor analysis, optical properties), Jia, UofT (modeling), von Salzen, EC, UVic (modeling), Martin, Dal (modeling) Collaborators: Cziczo, MIT (PCVI and residual analysis expertise), Huang, EC (EC/OC, carbon isotope measurements), Li, EC (SP2; aerosol chemistry), Liu, EC (particle measurement), Macdonald, EC (Whistler measurements, CVI expertise), Russell, Scripps (STXM/FTIR measurements of filter samples), Sharma EC(Arctic, snow measurements), Staebler, EC (Arctic air quality measurements), Law/Thomas LATMOS, France (modeling), Herber, AWI (measurements), Schneider, MPI (measurements)

Why Black Carbon (BC)? Relative to OC, BC in remote regions, particularly the Arctic, is well studied. However, there remain many unknowns concerning BC, and the ability of models to represent BC for climate and mitigation is at best poor. BC aerosol directly warms the atmosphere by absorption of solar radiation. Bond et al. (2013) estimate global direct radiative forcing of BC from industrial sources at W/m2 with 90% bounds of and W/m2. Light absorption by BC deposited to snow or ice surfaces enhances melting of the snow or ice surface (e.g. McConnell et al., 2007; Bond et al., 2013). The degree of scavenging of particles containing BC by clouds and its deposition to the Arctic ice and snow is poorly constrained in models, despite predictions of BC loadings being highly sensitive to this parameter [Koch et al., 2009]. As a primary emission of incomplete combustion (anthropogenic and biomass burning), BC may play a fundamental role in defining the aerosol size distribution, which means that it also possesses atmospheric cooling potential (e.g. Chen et al., 2010). For one discussion of terminology, see Petzold et al., Atmos. Chem. Phys., 13, 8365–8379, 2013.

Fossil and biofuel BC emissions (ng/m 2 /s) for 2008; from Sand, M. et al. Arctic surface temperature change to emissions of black carbon within Arctic or midlatitudes, JGR-Atm., From A. Stohl et al., Atmos. Chem. Phys., 13, , 2013 BC in the Arctic Representative modelling of transport within and above the Arctic dome is critical. (JB) Quinn et al., AMAP, 2011

Stohl et al model from Stohl et al., Atmos. Chem. Phys., 13, , 2013; Alert observations are and based on PSAP using a MAC of 10. Alert Time Series EC and OC from ; rBC is from (from Leaitch et al., Elementa, 2013). OC/EC is about 3 during haze period and 6 in the summer. The comparison of the simulations and the observations in this case indicate reasonable prediction for the surface. The discrepancy between the observations and the model in Stohl et al among other things indicates the importance of understanding the differences among the various techniques used to measure or estimate BC (Quinn and Bates, JGR, 2005; Bond et al., 2013). But the models aren’t perfect either… Alert observations Stohl et al model

From Stohl et al., Atmos. Chem. Phys., 13, , 2013 Profiles Despite reasonable agreement between the model and the observations near the surface, the observations suggest a larger BC burden than predicted by Stohl et al. Overall the numbers of observations are too limited to draw a conclusion, except that more profile observations and model comparisons are important. Approx 26 profiles From Sharma et al., JGR-Atm., 118, 2013 for (flaring emissions?).

BC Size Distribution – does it matter? BC is often viewed in isolation from other aerosol components. Understanding the BC and how it affects climate requires more knowledge (and predictive capability) of its size distribution and its interaction with other components of the aerosol in remote regions of the globe. The MAC coefficient that is used to convert light absorption to BC mass is strongly dependent on the size of BC and how it is combined with other aerosol components. The degree of coating, the morphology of the BC inclusion(s) and the size of the BC inclusions control the effectiveness of BC as a warming agent. (SH) BC unlikely? BC probable BC possible Quinn et al., AMAP, 2011

From Bond et al., JGR, 2013 – Effect of dust deposition on BC deposition

Why Organic Carbon (OC)? OC results from secondary production (oxidation of VOCs from biogenic, BB and anthropogenic sources) as well primary emissions (anthropogenic and biomass burning). Natural sources, such as biogenic emissions of terpenes, are significant sources of OC. OC plays a fundamental role in defining the aerosol size distribution, due to primary emissions and also due to secondary processes involving organic components affecting nucleation (Almeida et al., Nature, 2013) and growth rates of Aitken particles (Riipinen et al., ACP, 2011). Studies of OC in remote regions, particularly the Arctic, are few. At Alert, OC from biogenic VOC oxidation has been identified (specifically isoprene) in early June by Fu et al. (EST, 2009), a result that is consistent with the higher OC/EC value measured at Alert during summer. VOCs will also result from biomass burning and, during the Arctic Haze period, various anthropogenic sources including flaring. Light absorption by OC, or brown carbon, happens at lower visible wavelengths. Mass absorption by brown carbon for biomass burning plumes transported into the Arctic can be significant at blue wavelengths (McNaughton et al., ACP, 2011).

NETCARE’s Carbonaceous Aerosol Questions What is the relative importance of the mechanisms for BC and OC deposition to Arctic snow and ice, and what evidence is there for deposition in the boundary layer or via ice clouds? Does BC influence ice clouds (Coupled with Theme 2), which may enhance the deposition? What is the vertical distribution of BC and OC in the Arctic atmosphere? Can we clearly identify source regions for EC and OC? What are the levels and sources of BC and OC, including brown carbon, in snow? What are the implications of carbonaceous loadings in snow for radiative forcing? How do BC and OC loadings from biomass burning compare with anthropogenic BC and OC over the Arctic and Western Canada? Will an increase in boreal forest fires in a warmer climate may lead to more black carbon transport to remote regions. Can we predict the observed optical properties of the aerosol in remote Canada? (Coupled to theme 4) What would be the consequences of reducing or eliminating BC? (Coupled to theme 4)

BC and OC Activity Overview New ambient measurements of BC and OC New observations will be made of BC and OC loadings, mixing state, size distributions, cloud- nucleating properties, and optical properties. The observations will cover a large range of environments from the ground to the free troposphere at the sites shown to the left; the Lancaster Sound measurements will be from the CCGS Amundsen. Two intensive sets of measurements using the AWI POLAR 6 aircraft will be conducted: in summer 2014 from Resolute in coordination with the Amundsen, and in spring 2015 PAMARCMIP style (including Alert and Resolute). Together with model simulations (Theme 4) and source-receptor analysis, these observations will be used to: –improve the BC and OC source contributions,; –examine the single scattering albedo (SSA) and the potential influence of coatings on the SSA; –Study the contribution from carbonaceous aerosol to absorption in the atmospheric column relative to absorption from surface deposition. –understand the balance between warming from absorption by BC and brown carbon versus the cooling influence from the effects of BC and OC on the aerosol size distribution.

NETCARE Plans for OC and BC Ground-based and airborne measurements at Resolute and Alert will be used to characterize the Arctic Haze phenomenon, Asian trans-oceanic pollution transport, biomass burning plumes, potential sources of particles from the marginal ice zone and the short-term evolution of ship emissions. The spring measurements will also measure ice crystals to look for associated changes in BC. The new Whistler high elevation site measurements will be used to characterize aerosols from biomass burning and long range transport from Asia and to assess their impacts. We will determine background levels and optical properties of carbonaceous aerosol, as well as the impact of long range transport from Asia to Western North America upon this background. Source apportionment techniques will be applied to measurements of aerosol particles reaching the Whistler and Alert sites. A focused campaign at Alert will conduct measurements downstream of a ground- based counter flow virtual impactor (CVI) to measure the scavenging fraction of BC and OC as a function of size for ice particles. BC and OC loadings, including brown carbon, in snow at remote sites will be quantified to enable better estimates of the warming from reduced snow albedo. Source receptor-modeling will be applied to the snow constituents to provide information about the sources of BC and BB.