Vancouver B.C., Ozone Study

Principal Investigator:

R.M. Banta

Background:

During the fair weather conditions that lead to photochemical pollution episodes in Vancouver, B.C., and the Lower Fraser River Valley (LFV) nearby, thermally forced daytime upvalley flows carry pollutants northward into the many tributary valleys. These "finger-lake" valleys cut through the mountain range to the north of the LFV. At night thermally forced downvalley flows carry the polluted air out of the valleys and back into the LFV. Here, we study the chemistry and meteorological characteristics of the nocturnal flow out of one of the major tributary valleys, the valley of Pitt Lake, to investigate changes in the air mass occurring in the tributary valley.

Sample Findings

Review Poster: Doppler Lidar Observations of Nocturnal Cleaning Flows from a Tributary Valley near Vancouver, B.C. .

Some Observed Features:

Lower Fraser Valley
Surface-wind at Harris Road
Profiles of Pitt Lake valley flow & aerosol backscatter
Nonuniform outflow--core of outflow jet contained cleanest air
7-8 ms^-1 outflow jet from Pitt Lake valley

Some Discoveries

Nighttime outflow from Pitt Lake valley cleansed of O3, aerosols, and several other pollutants
Outflow jet not uniform across valley cross section: much variability in fixed-sensor measurements attributable to meander of this jet
Declines in pollution concentration:

1-2 August: fresh pollution implies titration with NO a factor; Ox also declines, indicating dry deposition

4-5 August: air with aged pollution, O3 and Ox decline together, implies dry deposition major removal process

2-3, 3-4 August: more complicated--much of observed variability probably due to meander of outflow jet
Dry deposition most likely occurs in downslope flows along forested sidewalls of Pitt Lake valley.
Interpretation of chemistry and meteorology data interdependent

References:

Banta, R.M., P.B. Shepson, J.W. Bottenheim, K.G. Anlauf, H.A. Wiebe, A.J. Gallant, T. Biesenthal, L.D.Olivier, C.-J. Zhu,I.G. McKendry, and D.G. Steyn. "Nocturnal cleansing flows in a tributary valley." Atmospheric Environment, 31, 2147-2162 (1997).

McKendry, I.G, D.G. Steyn, R.M. Hoff, W. Strapp, K. Anlauf, F. Froude, B.A. Martin, R.M. Banta, and L.D. Olivier. "Elevated pollution layers and vertical downmixing over the Lower Fraser Valley, B.C." Atmospheric Environment, 31, 2135-2146 (1997).

Pottier, J.L., S. Pryor, and R.M. Banta. "Synoptic variability related to boundary layer and surface features observed during Pacific '93." Atmospheric Environment, 31, 2163-2173 (1997).

McKendry, I.G, D.G. Steyn, R.M. Banta, W. Strapp, K. Anlauf, and J.L. Pottier. "Daytime air quality and local circulations in the Pitt Lake tributary valley, B.C." Journal of Applied Meteorology, 37, 393-404 (1998).