Quantifying the health effects of air pollution

Air pollution epidemiological studies tend to relate effects on health to concentrations of air pollutants

Where associations between exposure to air pollutants and health effects/ deaths are identified, the strength of evidence and whether they are likely to be causal is considered. The relationship between effects and concentration is represented by a coefficient.

Several studies have estimated the effects of air pollution on GP appointments, working days lost, hospital admissions for respiratory and cardiovascular reasons and the death rate. 

After reviewing the evidence COMEAP has made a number of recommendations of coefficients for short- and long-term exposure to a number of air pollutants, see tables 1 and 2 below.

Using coefficients, data on concentrations of the specified pollutant and baseline rates for the health outcome the size of the effects on health caused by the pollution can be quantified see section calculating burden and impact below.

 

Air pollution epidemiological studies tend to relate effects on health to concentrations of air pollutants

Where associations between exposure to air pollutants and health effects/ deaths are identified, the strength of evidence and whether they are likely to be causal is considered. The relationship between effects and concentration is represented by a coefficient.

Several studies have estimated the effects of air pollution on GP appointments, working days lost, hospital admissions for respiratory and cardiovascular reasons and the death rate. 

After reviewing the evidence COMEAP has made a number of recommendations of coefficients for short- and long-term exposure to a number of air pollutants, see tables 1 and 2 below.

Using coefficients, data on concentrations of the specified pollutant and baseline rates for the health outcome the size of the effects on health caused by the pollution can be quantified see section calculating burden and impact below.

 

Coefficients for quantifying short-term exposure to air pollution

    

Pollutant

 

Health Endpoint

Coefficient

PM10

Deaths (all causes)

 

 

Respiratory hospital admissions

 

 

Cardiovascular hospital admissions

+0.75% per 10 µg/m3   increase of PM10

24 hour mean

 

+0.8% per 10 µg/m3   increase of PM10

24 hour mean

 

+0.8% per 10 µg/m3   increase of PM10

24 hour mean

 

Sulphur dioxide

(SO2)

Deaths (all causes)

 

 

Respiratory hospital admissions

+0.6% per 10 µg/m3  increase of SO2

24 hour mean

 

+0.5% per 10 µg/m3   increase of SO2

24 hour mean

 

Nitrogen dioxide (NO2)

Respiratory hospital admissions

+2.5% per 50 µg/m3   increase of NO2

24 hour mean

Ozone (O3)

Deaths (all causes)

 

 

Respiratory hospital admissions

+ 3.0% per 50 µg/m3   increase of O3

8 hour mean

 

+ 3.5% per 50 µg/m3   increase of O3

8 hour mean

 

 

Table 1 Estimates of coefficients to quantify short-term exposure to pollutants

Quantification calculations should use either all-cause mortality or cause-specific i.e. cardiopulmonary mortality or lung cancer mortality

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

Respiratory conditions 

In 1998 COMEAP were asked by the Department of health to advise on the number of people in the UK whose health was affected by exposure to air pollution.The committee recommended estimates of the effects of short-term exposure to air pollution on deaths and admissions to hospital for respiratory conditions. 

Cardiovascular conditions

In 2001 COMEAP recommended an estimate for the effects of short-term exposure to particles on admissions to hospital for cardiovascular conditions.
 
See links for COMEAP related documents below.
 

Coefficients for quantifying long-term exposure to PM2.5

  

Health Endpoint

Coefficient

 

All-cause mortality

 

 

 

 

 

 

1.06

95% confidence interval 1.02-1.11

 

(+ 6% per 10 µg/m3 increase in PM2.5)

 

 

For impact assessment of all cause mortality and assessing policy interventions designed to reduce levels of air pollutants

Use the full distribution of probabilities  see report for details

 

1.01 and1.12 as the 12.5th and 87.5th percentiles of the probability distribution

For sensitivity analysis

1.00 and 1.15  

 

For reports on quantification of risks from long-term exposure to particulate air pollution represented by PM2.5

Cardiopulmonary mortality

 

1.09 95% confidence interval 1.03-1.16

 

 

Lung cancer mortality

1.08 95% confidence interval 1.01-1.16

 

 

All coefficients expressed in terms of relative risk per 10 µg/m3 increase in PM2.5 (annual average concentration).

Table 2 Estimates of Coefficients to quantify long-term exposure to fine particulate matter (PM2.5). 

 

By 2009, the evidence on the effects of long-term exposure had grown to enable COMEAP to recommend quantification of the effects from long-term exposure to particulate matter

In 2010 the mortality effects of long-term exposure to fine particulate matter was quantified.COMEAP used detailed calculations to quantify the effect on mortality of long-term exposure to PM2.5 in the UK, based on data for 2008. See the next section: calculating the burden and impact of air pollution. 

Quantifying the effects of long-term exposure to PM on Morbidity

The calculations of the mortality burden of particulate air pollution and the impact of reductions in pollution are based on cohort studies. These studies deal with the relationship between long-term concentrations of fine particles and risks of death. They tell us little or nothing about the effects of such exposure on indices of ill-health other than death. COMEAP is currently exploring the possibility that long-term exposure to fine particles might be linked with the prevalence of chronic respiratory disease in the population.

 

Calculating the burden and impact of air pollution

 

It is important to understand both the burden to public health imposed by exposure to particles and also the benefits to public health that might be delivered by policies designed to reduce ambient concentrations of particles

 

Impact/benefit to health of reductions in concentrations of fine particles

In considering benefits likely to be delivered by policies designed to reduce concentrations of particles calculating the gain in years of life lived by the population is the most appropriate way of representing the effects.

 

What would be the benefit in terms of mortality of reducing the annual average concentration of PM2.5 by 1 μg/m3?

Each 1 μg/mreduction in annual average concentration of PM2.5, would increase life expectancy from birth by 20 days and the whole population (including new births) would in total live about four million years longer over the next 106 years.

If all particulate air pollution from human activity (traffic, industry etc.) in 2008 was removed and air pollution kept at non-man made levels what would be the benefits in terms of reduction of mortality?

If it were possible to remove all human-made particulate matter, average life expectancy from birth would increase by six months, and the predicted gain would be 36.5 million years of life amongst the UK population over the next hundred years. 

 

Burden imposed by current concentrations of particles

The burden can be represented most vividly as equivalent to a calculated number of deaths per year, but reference to the associated loss of life should also be made.

  

What is the effect of air pollution on death in the UK today?

Using 2008 figures, the burden of particulate air pollution from human activity (traffic, industry etc.) was estimated as a loss of 340,000 years of life in 2008. This loss of life is an effect equivalent to 29,000 deaths in 2008The burden can also be represented as a loss of life expectancy from birth of 6 months (as an average across all births).

The key point is that although the effect of current levels of fine particles (monitored as PM2.5) on health can be calculated as equivalent to 29,000 deaths per year this is NOT to say that 29,000 people die each year solely as a result of exposure to fine particles. The reason for this is that fine particles contribute to, rather than cause entirely, the deaths of individuals.

The major effect of air pollution on deaths is from cardiovascular disease. It is likely that air pollution acts as a contributory factor - along with many others - in affecting mortality. COMEAP therefore speculates that the number of cardiovascular deaths in 2008 (approx 200,000) is more likely the maximum number of early deaths to which air pollution contributed a part.

If this number were affected, the average loss of life due to air pollution would have been less than 2 years each among those affected, though the actual amount could vary between individuals.

  

 

Read COMEAP’s discussion of burden and impact in the 2010 report The Mortality Effects of Long-Term Exposure to Particulate Air Pollution in the United Kingdom, see related comeap documents below

 The quantified health impacts of air pollution can assist with evaluating the costs and benefits of potential policy measures designed to improve air quality. Read about this in the economic costs of air pollution and Policy measures to improve air quality are set out in The UK Air Quality Strategy. See links to these pages below.