Effects of outdoor air pollutants on human health
Submitting InstitutionSt George's, University of London
Unit of AssessmentPublic Health, Health Services and Primary Care
Summary Impact TypeEnvironmental
Research Subject Area(s)
Medical and Health Sciences: Public Health and Health Services
Summary of the impact
A sustained programme of epidemiological research at St George's,
spanning 20 years, has informed air pollution control policies in the UK
and internationally. Time-series studies of the acute health effects of
daily fluctuations in air pollutants, initially in London, were extended
to Europe-wide collaborations, trans-Atlantic comparisons and studies in
Asian cities. Publication bias has been explored systematically in
meta-analyses of published time-series results, and the adverse effects of
different particulate fractions compared in a UK setting. This evidence
base has contributed substantially to the current UK Air Quality Strategy
and informs ongoing debates about health impacts of shorter-lived
In the early 1990s, the UK Department of Health convened an expert panel
which developed into the Committee on the Medical Effects of Air Pollution
(COMEAP). Three epidemiologists from St George's (Anderson, Atkinson and
Strachan) have served at length on COMEAP and associated committees over
the past two decades, a period which has seen outdoor air pollution
re-emerge as a public health concern.
All three have been in continuous employment at St George's since 1993.
Anderson has been professor of epidemiology and public health throughout.
Atkinson was initially a research fellow working with Anderson and was
promoted to senior lecturer in epidemiology in 2009. Strachan was
initially senior lecturer in epidemiology and was promoted to professor in
An early stimulus to this renewed interest in air pollution was the
observation that daily fluctuations in ambient levels of several
pollutants were associated with short-term variations in both fatal and
non-fatal health events at concentrations well below air quality standards
of the time. Our studies of daily mortality in London during 1987-1992 
showed that ozone levels were associated with a significant increase in
all cause mortality on the same day; black smoke concentrations on the
previous day were significantly associated with all cause mortality; and
significant but smaller adverse effects were observed for fluctuations in
nitrogen dioxide and sulphur dioxide.
Embellishment of this approach and its extension to 12 European cities as
part of the APHEA collaboration confirmed that, even at historically low
ambient levels, airborne particles had detectable short term effects on
mortality  and respiratory hospital admissions . The consistency of
the results across cities with wide differences in climate and
environmental conditions suggested that these associations may be causal.
As published evidence accumulated to support short-term associations
between air pollution levels and adverse health effects, three
methodological issues required investigation:
Firstly, whether developments of the time-series methodology through the
1990s could explain differences in the results obtained from various
studies. This was addressed by the APHENA project which re-analysed, using
a standardized methodology, the largest time-series studies of mortality
from Europe and North America . The findings obtained with the new
standardized analysis were generally comparable to those obtained in the
earlier studies, and were relatively robust to the data analysis method
used. This led to greater confidence in their relevance to public policy
on both sides of the Atlantic.
A second issue was whether selective publication and citation of
"positive" results, or undue focus on the most statistically significant
lag period between pollution measurement and health outcome, could have
overstated the epidemiological evidence. Our review of time series
analyses published up to 2002  concluded that publication bias is
present in single-city time-series studies of ambient particles, and that
differential selection of positive lags may also inflate estimates.
However, short-term associations between particles and adverse health
effects remained positive and significant after correcting statistically
for publication bias.
A third issue of policy relevance was which components of the particulate
mixture (size, number, source, toxicity) are most relevant to health. We
investigated associations of a range of particle metrics with daily deaths
and hospital admissions in London . This is one of few studies to
investigate particle numbers, rather than mass concentration, and found
that particle numbers were associated with daily mortality and admissions,
particularly for cardiovascular diseases whereas fluctuations in secondary
particles (nitrate and sulphate) were more important for respiratory
References to the research
 Katsouyanni K, Touloumi G, Spix C, Schwartz J, Balducci F, Medina S,
Rossi G, Wojtyniak B, Sunyer J, Bacharova L, Schouten JP, Ponka A,
Anderson HR. Short-term effects of ambient sulphur dioxide and particulate
matter on mortality in 12 European cities: results from time series data
from the APHEA project. Air Pollution and Health: a European Approach. Br
Med J 1997;314:1658-63. PMID:9180068. doi: http://dx.doi.org/10.1136/bmj.314.7095.1658
 Atkinson RW, Anderson HR, Sunyer J, Ayres J, Baccini M, Vonk JM,
Boumghar A, Forastiere F, Forsberg B, Touloumi G, Schwartz J, Katsouyanni
K. Acute effects of particulate air pollution on respiratory admissions:
results from APHEA 2 project. Air Pollution and Health: a European
Approach. Am J Respir Crit Care Med 2001;164:1860-6.
PMID:11734437. doi: 10.1164/ajrccm.164.10.2010138
 Katsouyanni K, Samet JM, Anderson HR, Atkinson R, Le Tertre A, Medina
S, Samoli E, Touloumi G, Burnett RT, Krewski D, Ramsay T, Dominici F, Peng
RD, Schwartz J, Zanobetti A; HEI Health Review Committee. Air pollution
and health: a European and North American approach (APHENA). Res Rep
Health Eff Inst 2009;142:5-90. PMID: 20073322. No DOI available.
 Anderson HR, Atkinson RW, Peacock JL, Sweeting MJ, Marston L. Ambient
particulate matter and health effects: publication bias in studies of
short-term associations. Epidemiology 2005;16:155-63.
PMID:15703529. DOI: 10.1097/01.ede.0000152528.22746.0f
 Atkinson RW, Fuller GW, Anderson HR, Harrison RM, Armstrong B. Urban
ambient particle metrics and health: a time-series analysis. Epidemiology
2010;21:501-11. PMID: 20502338. doi: 10.1097/EDE.0b013e3181debc88
Details of the impact
The European Union (EU) has designated 2013 to be the "Year of Air"
during which a comprehensive review of the air quality policies has been
undertaken. To inform this review, the REVIHAAP (Review of Evidence on
Health Aspects of Air Pollution) project was co-funded by the EU DG
ENVIRONMENT and WHO Regional Office for Europe, to answer 24
policy-related questions about air pollution and health. Included in this
review was consideration of whether new evidence was sufficient to revise
the WHO 2005 Air Quality Guidelines, published in 2006 [A]. Anderson was a
member of the REVIHAAP Scientific Advisory Committee and Atkinson was an
expert advisor and contributor to the report, especially sections on
The following sections of the REVIHAAP July 2013 report [B] refer to the
Air Pollution Epidemiology Database (APED) which is a systematic review
facility established at St George's to provide continuously updated
meta-analyses of time-series evidence, as described in document REF3a.
APED incorporated the results of the underpinning time-series studies into
a cumulative meta-analysis, commissioned specifically for the REVIHAAP
- Pages 52-55 & table 2: Use of ozone coefficients from APED,
including APHENA 
- Pages 74-76 & table 5: Use of NO2 coefficients from APED
- Pages 145-149 & table 11: Use of SO2 coefficients from APED
- Pages 217-218: References (APED cited as Anderson HR et al.
2007, but see REF3a.)
Linked with REVIHAAP, and extending from it, the HRAPIE (Health Risks of
Air Pollution in Europe) review [C] recommends concentration-response
functions for cost-benefit analysis to guide future policies for air
pollutant control. Anderson is a member of the Scientific Advisory
Committee and Atkinson is an advisor and contributor of evidence to
HRAPIE. Coefficients from time-series studies provide the key evidence
base for estimating response functions and cost-benefit analyses for all
Also, the observation that time-series analyses show similar effects of
short-term fluctuations in PM on health outcomes worldwide [D] buttresses
the argument that there is a causal association between respirable
particulate exposures and diverse health outcomes, including
non-respiratory mortality. This conclusion, linking time-series work with
chronic effects of PM, was also reached by the UK Department of Health
COMEAP in 2010 [E].
Results from time-series studies also underpin the 2011 COMEAP subgroup
report on UK Air Quality Standards, on which Anderson was a committee
member [F]. This used APED to update the WHO 2005 Air Quality Guidelines
[A] from which was developed a Daily Air Quality Index (DAQI) with
bandings indicating likely short-term health effects. The DAQI is now
implemented as a public information system online [G] and during periods
of high air pollutant levels, health warnings are incorporated into
national weather forecasts for the UK.
Time-series methods have been extended to studies of the effects of heat
waves and climate change. Although sulphate is a cooling agent, black
carbon and ozone could together exert nearly half as much global warming
as carbon dioxide. The complexity of these health and climate effects of
shorter-lived greenhouse pollutants needs to be recognised in mitigation
policies. Links between strategies to reduce greenhouse gases and public
health outcomes were reviewed in 2009 by a consortium in which Anderson
and Atkinson were involved [H].
Assessment of the relative importance of 67 risk factors, worldwide and
by region, formed part of the Global Burden of Disease 2010 project (GBD).
Anderson co-chaired the GBD subgroup assessing health effects of outdoor
air pollution, which evaluated both ambient particulate pollution and
ambient ozone [I]. An analysis of burden of disease due to air pollution
in the UK found that this had fallen by over 50% between 1990 and 2010,
reflecting mainly improvements in air quality over this time resulting
from effective environmental policies [J].
Sources to corroborate the impact
[A] WHO. Air Quality Guidelines, Global Update 2005. Particulate
Matter, Ozone, Nitrogen Dioxide and Sulfur Dioxide. World Health
Organization, Copenhagen, 2006. ISBN: 92-890-2192-6.
[B] REVIHAAP report (2013).
[Downloaded to PDF 11 July 2013]
[C] HRAPIE report (2013). http://www.euro.who.int/en/health-topics/environment-and-health/air-quality/publications/2013/health-risks-of-air-pollution-in-europe-hrapie-project.-new-emerging-risks-to-health-from-air-pollution-results-from-the-survey-of-experts
[Downloaded to PDF 15 November 2013]
[D] Atkinson RW, Cohen A, Mehta S, Anderson HR. Systematic review and
meta-analysis of epidemiological time-series studies on outdoor air
pollution and health in Asia. Air Quality Atmosphere and Health
[E] Committee on the Medical Effects of Air Pollutants. The Mortality
Effects of Long-Term Exposure to Particulate Air Pollution in the United
Kingdom. Health Protection Agency, 2010. ISBN 978-0-85951-685-3.
[F] Committee on the Medical Effects of Air Pollutants Standards Advisory
Subgroup. Review of the UK Air Quality Index. Health Protection
Agency, 2011. [PDF downloaded 11 July 2013]
[Downloaded to PDF 11 July 2013]
[H] Smith KR, Jerrett M, Anderson HR, Burnett RT, Stone V, Derwent R,
Atkinson RW, Cohen A, Shonkoff SB, Krewski D, Pope CA 3rd, Thun MJ,
Thurston G. Public health benefits of strategies to reduce greenhouse-gas
emissions: health implications of short-lived greenhouse pollutants. Lancet
2009;374:2091-103. PMID: 19942276.
[I] Lim SS, Vos T, Flaxman AD, ... Anderson HR, ... Lopez AD, Murray CJ,
Ezzati M. A comparative risk assessment of burden of disease and injury
attributable to 67 risk factors and risk factor clusters in 21 regions,
1990-2010: a systematic analysis for the Global Burden of Disease Study
2010. Lancet 2012;380:2224-60. PMID: 23245609.
[J] Murray CJ, Richards MA, Newton JN, Fenton KA, Anderson HR, Atkinson C
et al. UK health performance: findings of the Global Burden of
Disease Study 2010. Lancet 2013;381:997-1020 PMID: 23668584.