UV Radiation and the UV Index
An Ontario Perspective
Dave BroadhurstEnvironment Canada
Ontario UV Network ConferenceMay 10, 2007
www.ec.gc.ca
May 10, 2007 Page 2
Overview
• Factors affecting solar UV radiation
• UV radiation in Ontario
• UV Index and sun protection
• Long term recovery of the ozone layer
May 10, 2007 Page 3
Spectrum of Solar Radiation
May 10, 2007 Page 4
Filtering of UVR by the Atmosphere
NASA SOLVE Measurement Campaign
May 10, 2007 Page 5
Factors that Affect UV Radiation
• Sun angle (latitude, time of day and year)– Toronto January: 1.3; July: 8.7 – Edmonton January: 0.6; July: 7.7– Tropics January: 7.0; July: 14
• Cloud cover• Stratospheric ozone• Altitude• Smog, dust and haze• Reflection and shade
Global Solar UVI http://www.who.int/uv/uv_and_health/en/
Workshop (1995) http://www.phac-aspc.gc.ca/publicat/cdic-mcc/16-1/d_e.html
May 10, 2007 Page 6
Toronto 2007 Maximum UV Readings
Environment Canada, S&T Branch
May 10, 2007 Page 7
Winnipeg 2001 Maximum UV Readings
Environment Canada, S&T Branch
May 10, 2007 Page 8
UV Strength Through the Day
0
1
2
3
4
5
6
7
8
9
6:00AM
7:00AM
8:00AM
9:00AM
10:00AM
11:00AM
12:00PM
1:00PM
2:00PM
3:00PM
4:00PM
5:00PM
6:00PM
7:00PM
8:00PM
9:00PM
Time of Day (EDT)
UV
In
de
x
June or July
April or September
December or January
Typical Readings on Sunny Days in Southern Ontario
Environment Canada
May 10, 2007 Page 9
The UV Index
• Intensity of sunburning UV radiation
• Values may reach 10 in Ontario (15 in tropics)
• Included in weather forecast when maximum UV predicted to be ≥3 units
• Highest values 11 a.m. to 4 p.m.
• UV exposure = intensity X duration
http://www.msc.ec.gc.ca/topics/uv/
May 10, 2007 Page 10
UV Index – Sun Protection Actions
UVI Category
Sun Protection Actions
0 – 2 Low Minimal protection for normal activity
3 – 5 Moderate Take precautions if outside for ≥30 min
6 - 7 High Protection required. Reduce time in the sun between 11 am and 4 pm, seek shade, cover-up, wear a hat, sunglasses and sunscreen
8 - 10 Very High Take full precautions (see above) and avoid the sun between 11 am and 4 pm
11 + Extreme Very rare in Canada. Unprotected skin will be damaged and can burn in minutes
May 10, 2007 Page 11
Atmospheric Ozone over Canada
Fioletov, Environment Canada
May 10, 2007 Page 12
Projected Global Ozone Recovery
IPCC, Safeguarding the Ozone Layer, 2005
May 10, 2007 Page 13
Resources
EC UV Index site http://www.msc.ec.gc.ca/topics/uv/
EC weather forecasts http://weatheroffice.gc.ca/canada_e.html
UV/ozone graphs http://exp-studies.tor.ec.gc.ca/e/ozone/uv_plots.htm
UV Index Poster http://www.msc.ec.gc.ca/topics/uv/uv_health_e.html
UV Index Sun Awareness Program http://www.hc-sc.gc.ca/hl-vs/securit/sports/sun-sol/uv-prog/index_e.html
Skywatcher’s UV Chapter (#6) & activities 20-23 http://www.weatheroffice.pyr.ec.gc.ca/skywatchers/guide_e.html
WMO Scientific Assessment of Ozone Depletion http://esrl.noaa.gov/csd/assessments/2006/
Note: □ in URLs means underscore
