Issue link: https://hi.iaq.net/i/670243
for a threshold for health effects, there is more convincing evidence for effects above a certain level (35 ppb) than below, and this should be adopted as a cut-off point for analysis. The question of a threshold for NO 2 assessment is currently still under review, although a preliminary opinion of COMEAP in the UK is that there is unlikely to be a threshold at the level of the whole population (bearing in mind that this includes people in a variety of health states). 9 • The most-studied effects, on mortality and hospital admissions linked to short-term exposure to fine particles, capture only a small part of the range of the total health effects reported for air pollution. For policy evaluation, this makes it desirable to include other endpoints, but the question arises of how far one should proceed, given increasing uncertainty as one pursues endpoints for which the evidence base is limited. Variable conclusions on this point have been reached by different bodies, noting here that analysis for the European Commission and USEPA has tended to quantify a large number of endpoints, while analysis for the UK government has so far considered fewer. It is notable that the major quantification studies in the UK, European Union and USA have all come to the same conclusions on several of the most important of these questions, specifically that: 1 PM has significant effects on health 2 the mortality effects of long-term exposure to PM should be quantified without threshold and without distinguishing between different types of particle 3 these mortality impacts should be quantified using a response function in the order of a 6% change in impact per 10 μg/m 3 PM 2.5 . 6.2.2 Analysis of impacts in the UK COMEAP 2 provides a detailed account of the quantification of the mortality burden of exposure to PM 2.5 in the UK. Results are shown in Table 1, expressed in terms of deaths and the impact on longevity. The COMEAP report considers the meaning of the estimate of the number of deaths shown in Table 1, noting that effects are principally from cardiovascular disease, which has multiple established and likely causes at the population level, and almost certainly has a complex mixture of factors affecting initiation and progression at the individual level. On this basis, the reported number of deaths should be considered as more of a statistical construct, with air pollution playing some role in bringing forward the deaths of a larger number of people than the 28,861 shown in Table 1. Table 1. COMEAP results for effects of outdoor PM 2.5 exposure on mortality for the UK 2 Measure of mortality Impact Number of attributable deaths 28,861 Attributable deaths per 100,000 aged over 30 years 75 Burden on total survival (life-years lost) 340,000 Difference in life expectancy for the 2008 cohort (days) Females 194 Males 182 © Royal College of Physicians 2016 81 6 The heavy cost of air pollution