Abstract
Recirculation of pollutants is often invoked as a cause of degraded air quality episodes. In this modelling study, we investigated recirculation in order to explore its behaviour in the Lower Fraser Valley (LFV), British Columbia. HYSPLIT was used to produce trajectories from WRF output for seven severe episodes, covering the four main circulation regimes conducive to ozone episodes. Both internal and external recirculations within our domain of interest were observable, but they do not have the same frequency for all regimes.
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References
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Acknowledgments
Funding for the research was derived from the NSERC USRA grant to Annie Seagram, and from NSERC grants to Douw G. Steyn and Peter Jackson and from the British Columbia Clean Air Research Fund supported by the Fraser Basin Council, Fraser Valley Regional District, and Metro Vancouver.
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Questions and Answers
Questioner Name: Jeff Weil
Q: How sensitive was the recirculating trajectory (extent and time) to source/origin; e.g. being on valley floor or on sidewalls, was initial behavior affected by slope flows and being within a slope boundary layer?
A: We performed a very rough sensitivity test of the origin’s location, and noted that placing it further north significantly increased the number of north-south recirculations, which were generally linked to mountain-valley wind reversals. However, the initial position must be constraint to some degree, as we would like to investigate the release of precursor pollutants, which primarily originate near the downtown center of Vancouver and not within the valleys.
Questioner Name: Mark Janssen
Q: Would your results look any different if you only picked a trajectory that resulted in high ozone?
A: We did not investigate this since we wanted to focus on forward trajectories as a means of detecting recirculation. It would be very interesting to do as you suggested, and determine the impact to which recirculating trajectories affect ozone values observed at various stations. We would predict that trajectories that directly result in “high ozone” at a station would also show recirculation, as our results show a lot of this behaviour during most episodes.
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Seagram, A., Steyn, D.G., Ainslie, B. (2014). Modelled Recirculation of Pollutants During Ozone Episodes in the Lower Fraser Valley, B. C.. In: Steyn, D., Builtjes, P., Timmermans, R. (eds) Air Pollution Modeling and its Application XXII. NATO Science for Peace and Security Series C: Environmental Security. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-5577-2_49
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DOI: https://doi.org/10.1007/978-94-007-5577-2_49
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