THE EFFEC OF TROPOSPHERIC OZONE ON HUMAN
HEALTH
Executive Summary for the MSc thesis of Rachel Harris
CENTRE FOR ENVIRONMENTAL POLICY
IMPERIAL COLLEGE LONDON
Academic Year 2009-2010
Supervisor: Professor Nigel Bell and Professor Paolo Vineis
AIMS AND OBJECTIVES
The overall aim was to investigate the health impact of tropospheric ozone. The main objectives
were:

To identify whether or not there is a causal link between ozone and respiratory diseases

To assess the best method for investigating this link

To establish those most at risk from ozone
INTRODUCTION
Over the past half a century there has been grave concern over anthropogenic activity disturbing the
naturally occurring ozone of the atmosphere. This disruption has serious consequences for the
environment and for human health. At high concentrations ozone is known to threaten human health.
With climate change, an increased reliance on fossil fuels and a large scale shift to urban living, ozone
poses an ever greater risk to human health. Recent studied into tropospheric ozone and respiratory
illnesses have looked at hospital admission data and found contrasting evidence with regards to
whether or not ozone is having a detrimental effect on the health of the population.
There is much literature documenting a relationship between regional ozone concentrations and the
number of emergency visits to hospitals for respiratory diseases. However these studies lack
consistency with regards to their approach and analysis. To establish the seriousness of the threat that
ozone may pose, it is essential to understand the best and most accurate approach to assessing the
problem. Only then can firm conclusions on the effect of tropospheric ozone on public health be
drawn.
METHODOLOGY
Early research indicated that a broad scope approach to analyze the existing literature would be
suitable given the similarly broad array of published literature surrounding the issue of ozone and
respiratory diseases.
The project used a qualitative approach to examine the evidence, deduce
theories and to acquire and insight. This study will use a scoring system to critically review the
scientific evidence of published case studies. By scoring studied on the validity of their methodology
it is possible to establish how strong the association between ozone and respiratory disease actually is.
Through an extensive critical review those groups most vulnerable to the affects of ozone will be
identified so they may be protected in the future. In addition the study will identify, via the critical
review, the areas that require further investigations and how best to conduct such efforts.
ANALYSIS
To compare and summarise the literature Table 1. includes the four highest ranking studies of those
critically reviewed. Scores have been allocated to various components of each study’s method of
collecting the data that underpins their analysis and conclusions. This scoring system helps to assess
the quality of studies and the reliability of the data included and therefore results. Anderson et al
ranks the highest out of the nine studies analysed. The study faired particularly well for its thorough
recording of other confounding pollutants such as PM and NO2, other non pollutant confounding
factors such as weather and influenza epidemics. Anderson et al was the only study to independently
include pollen counts in the analysis. Such a thorough inclusion of confounding factors means this
study has come as close as possible to investigating the effects of ozone independently. However the
association between ozone and other air pollutants is a complicated relationship and it is impossible to
completely analyse ozone independently. Burnett et al and Ponce de Leon et al also scored highly
(Burnett et al 2001; Ponce de Leon et al 1996). All of them concluded that there was an association
between ozone levels and respiratory admissions.
4
Temperature,
humidity,
seasonal and
other cyclical
factors, day of
the week,
influenza
epidemic,
autocorrelation
4
4
Pollens
not
included
based
on
Anderso
n et al
study
0
1
Respiratory
complaints to
A&E, reported by
the patients not
diagnosed by
medical
professionals
Table 1. The four highest ranking papers that were critically reviewed.
3
0
Not
mentioned
0
All
hospitals
in
Toronto
1
Not
mentioned
0
Coding
area of
residents
unavailable
for study
0
Multiple
London
hospitals
1
12
1
Not
mentioned
0
Not
mentioned
0
16
London
hospitals
1
11
1
Not
mentioned
1
Not
mentioned
3
0-14
years,
15 -65
years,
65+
years
0
0-14
years,
15 -65
years,
65+
years
Sampling
Spread
Score
NO2,
SO2, CO,
PM10,
BS
3
Not
mention
ed
0
Children
less tha
2 only
0
Not
mentioned
Control
disease
Score
Atkinson
et al
1999
NO2,
SO2 , BS
Temperature,
humidity,
seasonal and
other cyclical
factors, day of
the week,
holidays,
influenza
epidemic,
autocorrelation
3
Nor
mention
ed
3
0-14
years,
15 -65
years,
65+
years
Score
Ponce de
Leon et
al 1996
5
Temporal trends
in admissions,
temperature,
humidity,
admission
biases
3
Emergency
admssions of
asthma to all
London NHS
hospitals,
collected by
Hospital Episode
System, only
visits that result in
admission to
hospital
Data collected
from the Ontario
Ministary of
Health for all
hospitals in the
area, only urgent
or emergrncy
admissions
included,
specifically only
children below 2
years
Emergency
admissions to
London hospitals
for medical
diagnosis, data
sourced from
Hospital Episode
Systems,
diagnosis used
from 73%, 76%,
85%, 88%, and
95% of the 5 years
of the study
Age
Groups
Volunteer
exposure
location
Score
NO2,
SO2, CO,
PM2.5,
PM10-2.5
4
Daily
counts
of
burch,
grass
and oak
pollen
are
included
Respiratory
disaese diagnosis
Score
Burnett
et al
2001
4
Time trends,
seasonal factors,
calendar effects,
influenza
epidemics,
temperature,
humidity, auto
correlation
Pollen
Score
Anderson
et al
1998
NO2,
SO2,
PM2.5,
PM10-2.5
Other
confounding
factors
Score
Other
pollutants
Score
Study
0
All NHS
hospitals
across
London
1
16
1
13
Total
Score
DISCUSSION, CONCLUSIONS AND IMPLICATIONS
Most of the studies found positive associations between ozone and respiratory diseases (Ponce de
Leon et al 1996; Anderson et al 1998; Burnett et al 2001; Lin et al 2008). However some studies
show contrasting evidence. It is difficult to know whether this could be due to a lack of
consistency in the methodology, geographical location, the confounding factors included or other
differences such as health care management, socio-demographics, family history or genetic
susceptibility of the populations under study (Lin et al 2008). Some of the studies reviewed
excluded other pollutants as confounding factors. Pollutants such as SO2 are well documented to
affect the respiratory system. A few studies have even failed to consider temperature and
humidity which makes it difficult to ascertain the association between weather and ozone on the
results (Lin et al 2008). Generally there does seem to be an association between ozone and
respiratory diseases, particularly in vulnerable individuals such as asthmatics.
Areas identified to be neglected in the literature and where further research is recommended:
-
The interaction between pollen and ozone on respiratory diseases.
-
The effect of ozone specifically on those who have high exposure rates to ozone such as
farmers and cyclists.
-
Ozone concentrations and respiratory disease in rural areas and developing countries.
-
The suitability of the statistical analysis used in the analysis of ozone and respiratory
diseases.
How this thesis could be improved:
-
Making the critical review quantitative through methods such as a meta-analysis
would have increased the credibility of the critical review.
REFERENCES
Anderson, H.R., Ponce de Leon, A. & Bland, J.M. (1998). Air pollution, pollens, and daily
admission for asthma in London 1987-92. Thorax. 53: 842-848.
Burnett, R.T., Smith-Doiron, M., Stieb, D., Raizenne, M.E., Brook, J.R., Dales, R.E., Leech,
J.A., Catmak. & Krewski, D. (2001). Association between ozone hospitalization for acute
respiratory diseases in children less than 2 years of age. 135: 444-452.
Lin, S., Bell, E.M., Liu, W., Walker, R.J., Kim, N.K. & Hwang, S.A. (2008). Ambient ozone
concentration and hospital admissions due to childhood respiratory diseases in New York State,
1991-2001. Environmental Research. 108: 42-47.
Ponce de Leon, A., Anderson, H.R., Bland, J.M., Strachan, D.P. & Bower, J. (1996). Effects of
air pollution on daily hospital admission rates for respiratory disease in London between
1987088 and 1991-92. Journal of Epidemiology and Community Health. 33(Suppl 1):S63-S70.