CHEMICAL CHARACTERISTICS OF NORTH AMERICAN OUTFLOW: INSIGHTS FROM CHEBOGUE POINT, NOVA SCOTIA Allen Goldstein, Dylan Millet, James Allan, Eben Cross, Rupert Holzinger, Jose-Luis Jimenez, Brent Williams, Doug Worsnop, and the ICARTT science team

Motivation and Background “The tailpipe of North America” (Bernard Firanski) (GEOS-Chem) How do North American emissions impact downwind atmospheric composition and chemistry? Develop a method to distinguish between different source types based on in situ measurements Apply method to: Chemistry of boundary-layer pollution outflow from the N.E. U.S. Budget of aerosol and gas-phase organic carbon This work:

Lessons from NARE 1993 Photochemistry over the Atlantic Ocean is significantly perturbed by North American pollution Vertical layering, inhomogeneity of pollution outflow Surface often isolated from overlying atmosphere Peak pollution at Chebogue Point observed during flow transition periods i.e. when trajectory uncertainty is highest Importance of biogenics e.g. HCHO 80% new carbon for all transport regimes [Tanner et al., 1996] VOC

Site Introduction In-Situ Gas-phase Speciated VOCs (GC/FID/MS, PTR/MS) Speciated NO y (TD-LIF) PANs (GC/ECD) CO, O 3, H 2 O, CO 2, met variables 222 Rn Hg In-Situ Aerosol Mass and chemical composition (AMS, TAG, filter) Number & size distribution (CPC, DMA, HTDMA) CCN Optical properties (scattering, absorption, opt. depth) Elemental composition (DRUM) Stable isotopes (SO 4 & NO 3 ) Remote Cloud and aerosol backscatter (Lidar) Radar wind profiler Ozone sondes Solar and IR irradiance

Distinguishing Between Sources: Chemical Factors U.S. Outflow Local Anthropogenic Local Biogenic Oxygenated VOCs + Biomass Burning Alkanes Isoprene Oxidation 57 Variables (in-situ observations) Factor Analysis 6 Factors (distinct source types)

Source Regions for Chemical Factors Local Wind DirectionBack Trajectories Allen White, NOAA/ETL Impact Periods for each factor: Factor Score > 1σ N

Chemical Factor Impact Periods 15% 5.0% 9.2% 15% 12% 16% FrequencyTimescale US Outflow Local Anthro Local Biogenic OVOC+BB Alkanes Isoprene Oxn U.S. outflow impacted Chebogue Point 15% of the time, on a timescale of 7 hours 7.0 h 1.6 h 3.6 h 3.1 h 2.9 h 4.9 h Periods when Factor > 1σ

U.S. Outflow: CO and O 3 O 3 and CO are enhanced by +18 ppb (56%) and +37 ppb (30%) during US outflow periods FLEXPART Transport Time Additional CO during US outflow periods mostly emitted 2-3 days prior Andreas Stohl, NILU

Aerosol Mass and Composition Submicron aerosol mass is >3X higher during US outflow periods OM fraction is highest during periods of 1 o & 2 o biogenic influence (62-72%) OM amount correlates with US outflow, OVOC+biomass burning, and isoprene oxidation

Budget of Organic Carbon: Gas Phase Anthropogenic hydrocarbons 30-40% of gas-phase organic carbon

U.S. Outflow: VOC Chemistry With the OVOCs, biogenic compounds make up 86-93% of the VOC OH reactivity OH Reactivity =   k OH,i [ i ] i

U.S. Pollution Outflow Impacted Chebogue Point 15% of the time on a 7 hour timescale O 3 and CO elevated by 18 and 37 ppb; aerosol mass loading higher by > 3x Budget of Organic Carbon: Particle Phase OM fraction highest (70%) during periods of biogenic influence OM amount loaded with US outflow, OVOC+biomass burning, and isoprene oxidation factors Strong indication of the importance of biogenic SOA Budget of Organic Carbon: Gas Phase Except during periods of local influence the budget of gas phase OC is dominated by the anthropogenic compounds and the mixed-source OVOCs On a reactivity basis biogenics and OVOCs are the most important under all flow regimes (90% of total VOC reactivity) Summary Acknowledgements NOAA Office of Global Programs Jen Murphy, Nathan Kreisberg, Jim Roberts, Susanne Hering, Megan McKay, and the Chebogue Pt team Allen White and Andreas Stohl for the trajectory and FLEXPART products