Janssen et al. the estimated effect of a 1-μg/m 3 increase in PM10 (0.05%). Studies on BCP and PM2.5. Less, but more recent, information was available from studies in which both PM2.5 and BCP were measured. Three studies provided estimates of PM2.5 and EC, both for all-cause mortal- ity and for cardiovascular mortality. Only two studies provided estimates for respira- tory mortality [Cakmak et al. 2009a; Klemm et al. 2004; Mar et al. 2000; Ostro et al. 2007; see Supplemental Material, Tables C1–C3 (http://dx.doi.org/10.1289/ehp.1003369)]. In pooled analyses, a 1-gμ/m 3 increase in PM2.5 was associated with a 0.19% increase (95% CI: 0.03, 0.35%) in all-cause mortality and a 0.29% increase (95% CI: 0.07, 0.50%) in cardiovascular mortality. For EC, a 1-μg/m 3 increase was associated with a 1.45% increase (95% CI: 1.32, 1.57%) in all-cause mortality and 1.77% increase (95% CI: 1.08, 3.08%) in cardiovascular mortality. Thus, expressed per mass unit, effect estimates are much larger (7–8 times) for EC than for PM2.5. However, if the ratio of the IQR for PM2.5:EC (~ 11) is taken into account, effect estimates were similar. Available information on the effect of PM and EC on hospital admissions or emer- gency department visits was even more limited than for mortality, and no pooled estimates could be calculated [Cakmak et al. 2009b; Ostro et al. 2009; Peng et al. 2009; Tolbert et al. 2007; Zanobetti and Schwartz 2006; see Supplemental Material, Table D1 (http:// dx.doi.org/10.1289/ehp.1003369)]. When expressed per 1-gμ/m 3 increase, effect estimates were generally 10–30 times higher for EC than for PM2.5. However, IQRs for EC were lower by a similar factor. For example, the ratio of the IQRs for PM2.5:EC from Zanobetti and Schwartz (2006) (8.9:1.0) was similar to the ratio of the effect estimates for pneu- monia with a 1-μg/m 3 increase in EC:PM2.5 (0.054:0.0037), suggesting comparable effects with a comparable change in exposure. Two-pollutant models of PM mass and BCP. In total, six papers included results of two-pollutant models that included a meas- ure of PM mass as well as BCP. They also included findings on mortality as well as hos- pital admissions and emergency department visits (Table 2). With one exception, effect estimates for BCP either increased or decreased ≤ 33% after adjusting for PM mass. In con- trast, adjusting for BCP substantially reduced most effect estimates for PM mass (effect esti- mates became negative in three of nine studies and decreased by > 50% in five of the six other studies), suggesting that the effect of BCP is more robust than the effect of PM mass. Studies on BCP and other PM compo- nents. In addition to the effects of BCP com- pared with PM mass, the relative health effects of BCP compared with other PM components are of interest. Specifically, we were interested in evaluating whether effects of BCP remained significant after the authors had adjusted for other potentially relevant components such as metals. Eight studies that reported effect estimates for EC and PM mass also reported estimates for PM components, including OC, sulfate, and metals (Cakmak et al. 2009a, 2009b; Klemm et al. 2004; Mar et al. 2000; Ostro et al. 2007, 2009; Peng et al. 2009; All-cause mortality Amsterdam, 1996 Amsterdam, 2001 Athens, 2001 Barcelona, 2001a Birmingham, 2001 Cracow, 2001 Le Havre, 2001a London, 1999 London, 2001a Netherlands, 2000a Paris, 2001b Paris, 2001a,c Rouen, 2001a W. Midlands, 2001a Pooled (random) PM10 BS –2 –1 0 1 2 3 4 Percent change per 10-µg/m3 increase (95% CI) Figure 1. Single-city, single-pollutant estimates for PM10 and BS and all-cause mortality. Year indicates year of publication. References: Amsterdam, 1996 [Verhoeff et al. (1996)]; Amsterdam, 2001 [Roemer and van Wijnen (2001a)]; Athens, Barcelona, Birmingham, Cracow, London, and Paris, 2001 [Katsouyanni et al. (2001)]; Le Havre, Paris, and Rouen, 2001 [Zeghnoun et al. (2001)]; London, 1999 [Bremner et al. (1999)]; the Netherlands, 2000 [Hoek et al. (2000)]; West Midlands, 2001 [Anderson et al. (2001)]. aCities included in the pooled estimate. bZeghnoun et al. (2001). cKatsouyanni et al. (2001). 1694 ovlume 119 | number 12 | December 2011 • Environmental Health Perspectives Sarnat et al. 2008). In general, effects per IQR increase in exposure were greater for EC than for most of the six other frequently reported components [Supplemental Material, Table E1 (http://dx.doi.org/10.1289/ehp.1003369)]. For cardiovascular mortality and morbidity, four of five studies reported significant asso- ciations with an IQR increase in OC, four of four reported significant associations with potassium, and three of four reported signifi- cant associations with zinc. Estimated effects of an IQR increase in EC on cardiovascular mortality and morbidity were significant in all five studies. For respiratory mortality and morbidity results were more diverse, with the strongest effects observed for EC in two stud- ies (Cakmak et al. 2009a, 2009b) and for OC and sulfate in three studies (Ostro et al 2009; Peng et al. 2009; Sarnat et al. 2008), and no significant (p < 0.05) effects for any of the measured components in a sixth study (Ostro et al. 2007). Three studies also reported estimated effects based on multipollutant models that included a variety of PM components [see Supplemental Material, Table E2 (http:// dx.doi.org/10.1289/ehp.1003369)]. Two studies conducted in Santiago, Chile, reported significant associations with mortality (total, cardiac, and respiratory) and hospital admis- sions (all nonaccidental and respiratory) for EC, OC, and 10–15 of 16 individual elements based on single-pollutant models, but effect estimates for only EC and OC remained sig- nificant after adjustment for all other pollut- ants measured (Cakmak et al. 2009a, 2009b). In a study on emergency department visits for cardiovascular and respiratory disease in 119 U.S. urban communities (Peng et al. 2009), seven major PM components were considered (sulfate, nitrate, silicon, EC, OC, sodium ion, and ammonium ion). These seven components in aggregate constituted 83% of the total PM2.5 mass, whereas all other com- ponents contributed < 1% individually. In single-pollutant models, cardiovascular admis- sions were significantly associated with same- day concentrations of five of seven major PM components, including EC. In multipollutant models with all seven components, only EC remained significant. For respiratory admis- sions, only same-day OC concentrations were significant, both in single-pollutant and in multipollutant models. In a study of associa- tions between hospital admissions for cardio- vascular and respiratory diseases in 106 U.S. counties that related admissions to the fraction of 20 elements to the total PM2.5 mass rather than the concentration, RRs for cardiovascular and respiratory hospitalizations were high- est in counties with high PM2.5 content of nickel, vanadium, and EC (Bell et al. 2009). Here, nickel was the most robust compo- nent in multipollutant analyses, especially for