Abstract
BackgroundFor many air pollution epidemiological studies in Europe, ‘black smoke’ (BS) was the only measurement available to quantify ambient particulate matter (PM), particularly for exposures prior to the mid-1990s when quantification via the PM10 and/or PM2.5 metrics was introduced. The aim of this work was to review historic BS and PM measurements to allow comparison of health concentration-response functions (CRF) derived using BS as the measure of exposure with CRFs derived using PM10 or PM2.5.MethodsThe literature was searched for quantitative information on measured ratios of BS:PM10, BS:PM2.5, and chemical composition of PM; with specific focus on the United Kingdom (UK) between 1970 and the early 2000s when BS measurements were discontinued.ResultsThe average BS:PM10 ratio in urban background air was just below unity at the start of the 1970s, decreased rapidly to ≈ 0.7 in the mid-1970s and to ≈ 0.5 at the end of the 1970s, with continued smaller declines in the 1980s, and was within the range 0.2–0.4 by the end of the 1990s. The limited data for the BS:PM2.5 ratio suggest it equalled or exceeded unity at the start of the 1970s, declined to ≈ 0.7 by the end of the 1970s, with slower decline thereafter to a range 0.4–0.65 by the end of the 1990s. For an epidemiological study that presents a CRFBS value, the corresponding CRFPM10 value can be estimated as RBS:PM10 × CRFBS where RBS:PM10 is the BS:PM10 concentration ratio, if the toxicity of PM10 is assumed due only to the component quantified by a BS measurement. In the general case of some (but unknown) contribution of toxicity from non-BS components of PM10 then CRFPM10 > RBS:PM10 × CRFBS, with CRFPM10 exceeding CRFBS if the toxicity of the other components in PM10 is greater than the toxicity of the component to which the BS metric is sensitive. Similar analyses were applied to relationships between CRFPM2.5 and CRFBS.ConclusionsApplication of this analysis to example published CRFBS values for short and long-term health effects of PM suggest health effects from other components in the PM mixture in addition to the fine black particles characterised by BS.
Highlights
For many air pollution epidemiological studies in Europe, ‘black smoke’ (BS) was the only measurement available to quantify ambient particulate matter (PM), for exposures prior to the mid-1990s when quantification via the PM10 and/or PM2.5 metrics was introduced
From the mid-1990s, ambient PM began to be quantified as PM10 and/or PM2.5, the total mass concentration of all particles within rigorously-defined size fractions, and these are the usual measure of PM exposure for epidemiological studies [3]
The analyses presented here of approximate Black Smoke’ (BS):PMx ratios at epidemiologically-relevant monitoring sites is consistent with epidemiology methods; and any ‘sub-population’ intra-urban variability does not negate the potential of deducing information from the relationship between concentration-response functions (CRF) for BS and for PMx at a given site
Summary
For many air pollution epidemiological studies in Europe, ‘black smoke’ (BS) was the only measurement available to quantify ambient particulate matter (PM), for exposures prior to the mid-1990s when quantification via the PM10 and/or PM2.5 metrics was introduced. Prior to the 1990s concentrations of ambient airborne particulate matter (PM) in Europe were largely quantified by the darkness of the particulate material collected on filter papers. In this ‘Black Smoke’ (BS) method, the proportion of white light reflected from the sample (essentially the complement of the darkness) was converted to a mass concentration of PM using a standard equation [1, 2]. The associations between concentrations of black particles and illhealth have been emphasised by the World Health Organisation [11] and others [12]
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