Initial Results from the Canadian Component of the Intercontinental Chemical Transport Experiment (INTEX-B)

Randall Martin1, Aaron van Donkelaar1, Tom Duck1, Qi Zhang2, Kurt Anlauf3, Richard Leaitch3,1, Shao-Meng Li3, Peter Liu3, Katherine Hayden3, Anne Marie Macdonald3, Desiree Toom-Sauntry3, Ian McKendry4

1Dalhousie University 2SUNY Albany 3Environment Canada4University of British Columbia

IntroductionGas and aerosol pollutants are routinely transported on intercontinental scales, and can influence air quality and regional climate downwind. The transport of Asian pollution to North America is episodic, but most frequent and rapid in spring due to enhanced frontal activity in eastern Asia and strong atmospheric westerlies. Efforts to improve air quality in North America through domestic emission controls could be thwarted by Asian industrialization and the associated trans-Pacific transport of pollution. However, there is still considerable uncertainty as to the implications of this trans-Pacific transport and its relevance for North American air quality and climate.

Ground-based Remote Sensing

OverviewA major international research initiative, the Intercontinental Chemical Transport Experiment (INTEX‑B), was designed to quantify the role of long-range pollution transport on environmental degradation. The Canadian component of this campaign focused on the implications of long-range transport from Asia to North America. The Canadian intensive included airborne and ground-based measurements of atmospheric composition near Whistler, British Columbia, over 23 April 2006 - 17 May 2006. Regular vertical profiles of aerosol chemical and physical properties, carbon monoxide (CO), and ozone (O3) were conducted from the Canadian Cessna 207 aircraft. The Dalhousie Raman Lidar measured aerosol optical

properties. Intensive measurements of CO, O3, mercury, and aerosol properties were conducted from the summit of Whistler (2182m).

Acknowledgements

SummaryThe Dalhousie Raman Lidar was deployed near Whistler, where it also captured distinct aerosol layers.

Airborne MeasurementsThirty-three flights were conducted with the Canadian Cessna 207 aircraft:

O3, CO (last 10 flights)

Particle chemistry (AMS, filter IC for SO42-)

Particle size (150 nm – 20 um)

Particle scattering (nephelometer)

This work was supported by the Special Research Opportunity Program of the National Sciences and Engineering Research Council of Canada.

532/607 nm

Backscatter R

atio

May 11 May 14

Four years of measurements. During the intensive:O3, CO, Hg

Particle size (10nm – 20um) Particle scattering & absorptionParticle chemistry (HR-ToF-AMS, Moudi for inorganics & metals, 24-hr bulk filters)

Organic aerosol dominates the measurements in 2006 (and also 2005). There was a major sulfate episode in mid-May 2006.

Whistler Summit (2182m)

The aerosol spectrum reveals that the organic aerosol is highly oxidized during the sulfate period. Correlation of the Whistler aerosol spectrum with previous Q-AMS measurements in rural British Columbia, and during ACE-Asia following the analysis by Zhang et al. (2005, 2006) provides supporting evidence of Asian influence during the high sulfate period, in contrast with regional influence during the high organic period.

ReferencesHeald, C.L., D.J. Jacob, R.J. Park, L.M. Russell, B.J. Huebert, J.H. Seinfeld, H. Liao, and R.J. Weber (2005), A large organic aerosol source in the free troposphere missing from current models, Geophys. Res. Lett., 32, L18809, doi:10.1029/2005GL023831. Martin, R.V., et al. (2006), Evaluation of space-based constraints on nitrogen oxide emissions with regional aircraft measurements over and downwind of eastern North America, J. Geophys. Res., D15308, doi:10.1029/2005JD006680.Zhang, Q., M.R. Alfarra, D.R. Worsnop, J.D. Allan, H. Coe, M.R. Canagaratna, and J.L. Jimenez, Deconvolution and quantification of hydrocarbon-like and oxygenated organic aerosols based on aerosol mass spectrometry, Environmental Science & Technology, 39 (13), 4938-4952, doi:10.1021/es048568l, 2005.Zhang, Q., D.R. Worsnop, M.R. Canagaratna, and J.L. Jimenez, Hydrocarbon-like and oxygenated organic aerosols in Pittsburgh: Insights into sources and processes of organic aerosols, Atmos. Chem. Phys., 5, 3289-3311, 2005.

The summit measurements (top) show a distinct transition from a sulfate dominated airmass, to an organic dominated airmass. GEOS-Chem simulations (right) show an aged sulfate plume arriving on the west coast of North America on the 14th, passing across Whistler summit (~800 hPa) on the 15th, and being advected northward on the 16th.

Case Study of the Sulfate to Organic Transition

Sulfate (ug/m3)

GEOS-Chem simulations at 800 hPa

5/14/2006 3AM PST

5/15/2006 8AM PST

5/16/2006 3AM PST

Sulfate (ug/m3)Sulfate (ug/m3)

4/21/2006 9PM PST

GEOS-Chem simulations at 675 hPa

4/21/2006 9PM PST 4/23/2006 3PM PST

Right panels show a plume measured during three flights over April 22-23. Simulations using the GEOS-Chem global model of oxidant-aerosol chemistry (below) show an aged sulfate plume to the west of North America on the 21st, passing over Whistler on April 22-23 where it was sampled by the aircraft. Biases could reflect a missing organic aerosol source (Heald et al., 2005) and underestimates in Asian NOx emissions (Martin et al. 2006).

Distinct plumes were measured from aircraft, lidar, and Whistler summit over the intensive. Plumes were measured with enhanced sulfate aerosol, organic aerosol, O3, and CO. GEOS-Chem simulations and analysis of the aerosol spectrum provide evidence that the sulfate plumes are of Asian origin. Bias in simulated organic aerosol and O3 could reflect underestimated sources.

Organic

Sulfate

Nitrate

Ozone

(preliminary for aircraft)

GEOS-Chem (dashed) versus aircraft (solid)