A chronology of ratios between black smoke and PM10 and PM2.5 in the context of comparison of air pollution epidemiology concentration-response functions

Table 1 Summary of estimates of historical UK average urban BS concentrations, and of individual and summed component concentrations in PM_2.5 and PM₁₀ (μg m⁻³). Summations of components assume individual ranges correspond to 4 sd of uncertainty (i.e. that ranges approximate to a 95% confidence interval) and use standard formulae for combinations of uncertainties. The same approach is used to combine uncertainties in PM_2.5:PM₁₀ splits with the ranges of individual components. Detailed explanation of how these values are derived is given in the Additional file 1. The bottom two rows provide the BS:PM_x ratios implied by this speciated approach and as inferred from the direct measurements discussed in Section 2

PM component	1970s	1980s	Late 1990s	PM_2.5/PM₁₀ split	1970s	1980s	Late 1990s
	BS				BS
	35	18	8		35	18	8
	PM₁₀				PM_2.5
(NH₄)₂SO₄	7–16	7–16	4–7	0.8–0.9	6–14	6–14	3–6
NH₄NO₃ + NaNO₃	3–7	3–10	3–10	0.5–0.7	2–4	2–6	2–6
NaCl	2–5	2–5	2–5	0.2–0.4	0.5–1.5	0.5–1.5	0.5–1.5
Dust	2–4	2–4	2–4	0.2–0.4	0.5–1.5	0.5–1.5	0.5–1.5
EC	8–10	4–5	2–3	0.7–0.9	6–9	3–4	1–2
OM	13–37	6–19	3–9	0.7–0.9	10–30	5–15	2–7
Total PM_x	44–70	33–50	21–31		31–53	23–36	13–20
BS:PM_x ratio (via speciated data)	0.5–0.8	0.35–0.5	0.25–0.4		0.65–1.1	0.5–0.8	0.4–0.6
BS:PM_x ratio (direct measurements)	≈0.7	≈0.5	≈0.3		0.7–1.1	0.5–0.8	0.4–0.65

ISSN: 1476-069X