Role of Weather Conditions Leading to Major Winter PM Episode January 31 to February 8, 2005

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Role of Weather Conditions Leading to Major
Winter PM Episode January 31 to February 8, 2005
Meteorological Service of Canada
Jacques Rousseau M.Sc. February 12, 2007
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Québec Air Quality Network
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PM2.5 average of 21 stations, TEOM
Smog Episode (9 days) January 31 to February
8, 2005
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Time Variation PM2.5
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Origins of air mass 5 days Backtrajectories
Air Flow
Surface Map February 6, 2005
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Keys Finding

• Smog spread slowly in St-Lawrence Valley from
  south-west to north-east at first then spread out
  of valley within 2 days
• Typically summer smog episode with broad surface
  ridge pressure along north-eastern U.S. coast
• Very light south-westerly flow allowing build-up
  of pollutants due to stagnation of the air mass
• Smog episode ended by cold front sweeping through
  regions

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Episode
Wind speed (Km/h)
Surface Temperature (0C)
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Wind Speed Relationship
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Temperature Dependency
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Maniwaki T-F
Temperature (oC)Dew point (oC)Wet bulb (oC)
February 6, 2005 12Z
February 7, 2005 00Z
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Planetary Boundary Layer
R2 0,49
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Mixing Height (m)
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Québec City February 2, 2005
Source M. Therrien MDDEP
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Mixing height (m)
Wind Speed (Km/h)
Ventilation Wind speed X Mixing height
Ventilation (m2/h)
Air Volume
Wind (m/s)
Mixing height (m)
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Vertical Stability (oC/m)
Stable Lapse
rate lt 1 oC / 100 m Unstable
Lapse rate gt 1 oC / 100 m
R2 0,34
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Vertical Stability (oC/m)
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Keys Finding

• Weather conditions favourable to poor
  dispersionbeginning 2 days prior of the episode
• Light surface winds
• Deep temperature inversion in low level
• Warm air advection in mid level keeping inversion
• Low mixing height
• Air mass very stable
• No ventilation

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CHRONOS Air Quality Model PM2.5 Scenarios
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Localemission(Québec)
February 5, 2005
Base line
Québec off
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5-10
USA emission
Ontario emission
USA off
Ontario off
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24 Hours Average PM2.5 February 2, 2005
Southern Québec Regions
(µg/m3)
Local emission from Montréal and Québec City
PM2.5 February 2, 2005
AirNow Data EPA DataFed.Net
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PM2.5 (Dichotomous) station Ontario street
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Speciation station Saint-Anicet
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SO2 and CO mixing ratio (ppb)
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NO O3 NO2 O2
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290
105
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Conclusion

• Broad surface ridge pressure with light
  southwesterly flow allowing pollutants to
  build-up
• Low mixing height and deep inversion in low level
  
• Air mass very stable throughout the period
• High level of Chloride, Calcium Sodium, due to
  road salt use
• Up to 70 of pollutants are from local emission
  (Quebec)
• Exceptional long lasting weather conditions
  favourable to poor dispersion are the main actor
  of this particle episode

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