Quantifying potential of shades
in diminishing human exposure
to solar UVB radiation
Anu Heikkilä, Ari Aaltonen, Antti Aarva & Antti Poikonen
Finnish Meteorological Institute
European Conference on Solar UV Monitoring
ECUVM
12-14 Sep 2018, Vienna, Austria
• Background and motivation
• Measurement setup
• First results on the data collected
Descriptive analysis
Elementary statistics
• Conclusions
• Outlook
Outline
Solar UV radiation has well established harmful effects on human health: erythema, photoaging, increased risk of skin cancers etc.
~90 % of skin melanoma incidences in Finland could be avoided by ”sun smart” behavior (Finnish Cancer Society 2016)
Human behavior is the predominant cause for the increasing trends of skin cancers over the last century (UNEP/EEAP 2018)
Background
National programs guide people to protect themselves
against the harmful effects of UV radiation by
1. Using protective clothing and sunglasses
2. Applying sunscreen lotions
3. Seeking shade
whenever UV index reaches or exceeds the value of 3
Background & motivation
”Sun smart” behaviour?
Finnish Cancer Society’s questionnaire (2016) on sun
protection measures in Finnish day care centers:
• Response rate: 33 % (293 / 900)
• Result: >25 % of the day care centers restrict
outdoor activities of children due to excessive
sun shine on the yard
• Major reason: Inadequate availability of shades,
especially on the yards of recently build centers
Motivation
A joint statement from the Nordic
radiation safety authorities (1/2)
Released 27 Apr 2017
title: Outdoor environments for children
must offer sun protected areas
A joint statement from the Nordic
radiation safety authorities (2/2)
Municipal administrations, urban planners and those
responsible for children [--] are advised to incorporate
measures that improve sun protection for children,
including:
1.“Increase the availability of shade in outdoor environments
in pre-school and school playgrounds, public parks and
recreational areas.”
2.“Provide children and their caretakers with the information
they need in order to make informed and healthy choices
regarding UV exposure from the sun.”
3.”Establish sun protection policies.”
Obvious need / obligation to set up a new
measurement experiment to:
1. Collect experimental data supporting planning
of ”sun smart” areas of daily outdoor activities
2. Test the validity and the limits of the general rule on
”Seek shade - > halve the UV exposure”
Motivation / obligation
Measurement setup
• Equipment:
Sun tracker 2AP (Kipp&Zonen) + a broadband UVB-meter (Solar Light) + a shadowing ball -> diffuse UVB
Existing UVB-meter (Solar Light) -> global UVB
• Place: Roof of the FMI head quarters in Helsinki, Finland (60.20N, 24.96E)
• Time resolution: 1 min
• Start: 28 Mar 2017
• Doserates or doses? • Appropriate metrics probably depend on
the time span of the effect considered • The following separation seems therefore meaningful: I. Instantaneous / short-term effects
~ avoidance of sunburns -> max daily UV index (erythemally weighted UVB doserate) could be considered
II. Long-term effects ~ avoidance of excessive total UVB exposure / accumulated UVB dose -> daily/monthly/annual doses perhaps represent the most appropriate quantity
Efficiency of shadowing – metrics?
Path of analysis adopted
I. Daily level: doserates / (daily max) UVI
and daily doses
---
II. Monthly level: Monthly doses
III. Seasonal level: Seasonal doses
IV. Annual level: Annual doses
UV-tiedotustilaisuus 9.4.2015
Data collected
• Time period 28 Mar 2017 – 31 Aug 2018
Global & diffuse UVI and cloudiness
Overcast days
Time period 28 Mar 2017 – 24 Apr 2017
Ratio diffuse UVI / global UVI
Min 0.48
Max 0.99
Shadowing effect on UVI
Reduction in daily max UVI due to shadowing
Min 1 %
Max 52 %
Shadowing effect on UVI
Reduction in daily max UVI due to shadowing
Shadowing effect on UVB dose
Reduction in daily UVB dose due to shadowing
Max 45 %
Min 3 %
Statistics on daily values
Reduction in daily max UV index and
daily UVB dose by shadowing:
Daily max UVI Daily UVB dose
max min ave max min ave
Mar-May 48 % 4 % 30 % 42 % 7 % 25 %
Jun-Aug 52 % 1 % 33 % 45 % 4 % 23 %
Sep-Nov 35 % 7 % 15 % 27 % 3 % 16 %
Dec-Feb 31 % 8 % 15 % 31 % 15 % 23 %
Monthly UVB doses
Monthly UVB doses
Min 0.66
Max 0.87
Reduction in monthly UVB dose
by shadowing
max 34 % May 2018
min 13 % Oct 2017
Seasonal UVB doses
Reduction in seasonal & annual
UVB doses by shadowing
GlobUVBdose (kJ m-2)
DiffUVBdose (kJ m-2)
Reduction by shadowing
Summer-2017 197 142 28 % Autumn-2017 34 29 15 % Winter-2017/18 9 7 21 % Spring-2018 131 92 30 % Summer-2018 227 168 26 %
GlobUVBdose (kJ m-2)
DiffUVBdose (kJ m-2)
Reduction by shadowing
Annual average 379 278 26 %
Conclusions
• On time period 28 Mar 2017 – 30 Aug 2018,
shadowing reduced erythemally weighted UVB by
1 – 52 % in daily max UV Index (doserate)
3 – 45 % in daily dose
• The rule of thumb on shade’s potential to even halve
the harmful UV exposure is still valid
• Reduction of UVB dose by shadowing was
13 – 34 % in monthly doses
15 % in autumn 2017 – 30 % in spring 2018
on average 26 % in annual dose
Outlook
How to improve the estimates on the potential
of shading structures outdoors in diminishing
harmful effects of UV radiation?
1. Restrict the analysis to UVI>=3 (protection limit)
2. Require the average UVI in a time window of x min
to reach/exceed UVI=3
3. Collect & incorporate data on human behaviour?
the actual hours of the day spent in outdoor activities
the amount of protective clothing
4. Account for the real orientation of the body parts?
Action spectrum?
• UVI / erythemally weighted doserate and
corresponding doses are appropriate for quantification
of short-term effects (sunburn)
• How representative the action spectrum for erythema
is for the long-term effects?
Acknowledgments
Reijo Visuri Radiation and Nuclear Safety Authority in Finland
(STUK)
Virve Laivisto & Eeva Ollila Finnish Cancer Society
11.10.2018 27
