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 periodsi.e. when trajectory uncertainty is highest

Importance of biogenicse.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 NOy (TD-LIF)

PANs (GC/ECD)

CO, O3, H2O, CO2, met variables

222Rn

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 (SO4 & NO3)

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

Analysis6 Factors

(distinct source types)

Source Regions for Chemical Factors

Local Wind Direction Back 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%

Frequency Timescale

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 O3

O3 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 1o &

2o 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 =kOH,i [ i ]i

U.S. Pollution OutflowImpacted Chebogue Point 15% of the time on a 7 hour timescale

O3 and CO elevated by 18 and 37 ppb; aerosol mass loading higher by > 3x

Budget of Organic Carbon: Particle PhaseOM 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 PhaseExcept during periods of local influence the budget of gas phase OC is dominated

by the anthropogenic compounds and the mixed-source OVOCsOn 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