Ambient air pollution burden of disease DALYs

As part of a broader project to assess major risk factors to health, the burden of disease resulting from exposure to ambient (outdoor) air pollution was assessed. Ambient air pollution results from emissions from industrial activity, households, cars and trucks which are complex mixtures of air pollutants, many of which are harmful to health. Of all of these pollutants, fine particulate matter has the greatest effect on human health. In high-income countries, urban outdoor air pollution ranks in the top ten risk factors to health, and is the first environmental risk factor.

The burden of disease attributable to ambient air pollution can be expressed as: number of deaths, death rate (both crude and age-standardized), number of disability-adjusted life years (DALYs), DALYs rate (both crude and age-standardized), and number of years life lost (YLLs). Death and DALYs rates are calculated by dividing the number of deaths or DALYs by the total population (or indicated if a different population group is used, e.g. children under 5 years, or children under 15 years). Age-standardized rates adjust for differences in population age distribution by applying the observed age-specific mortality (or DALYs) rates for each population to a standard population. The age-standardized rates can therefore be used to compare the rates of countries without being affected by the differences in age distribution from country to country. Evidence from epidemiological studies have shown that exposure to ambient air pollution is linked, among others, to the important diseases taken into account in this estimate: 1) Lower respiratory infections in general population, children under 5 years of age and children under 15 years of age; 2) Stroke in adults (25 years and over); 3) Ischaemic heart diseases in adults (25 years and over); 4) Chronic obstructive pulmonary diseases in adults (25 years and over); and 5) Trachea, bronchus and lung cancers in adults (25 years and over).

 

Estimates are available by age group and by sex.

Burden of disease is calculated by first combining information on the increased (or relative) risk of a disease resulting from exposure, with information on how widespread the exposure is in the population (in this case, the annual mean concentration of particulate matter to which the population is exposed). This allows calculation of the 'population attributable fraction' (PAF), which is the fraction of disease seen in a given population that can be attributed to the exposure, in this case the annual mean concentration of particulate matter. Applying this fraction to the total burden of disease (e.g. cardiopulmonary disease expressed as deaths or DALYs), gives the total number of deaths or DALYs that results from ambient air pollution.

For deaths, DALYs and YLLs, national figures are summed. For the corresponding rates, the country estimates are summed according to the region of interest and divided by the corresponding regional population.