Delfino et al. The first composited quarter­ section was was used to estimate method precision (> 20% Material, Regression Model, Mean Centering digested with concentrated acid using micro­ for all PAHs, hopanes, and na­lkanes). Method (doi:10.1289/ehp.0901407)]. We wave digestion followed by analysis to deter­ Statistical analysis. We analyzed relations decided a priori to adjust for 5­day average mine 52 trace elements using highr­esolution of repeated (within­subject) measures of bio ­ temperature. Magnitudes of association from inductively coupled plasma mass spectrometry markers to air pollutant exposures with linear the mixed models are expressed at pollutant (Finnigan Element 2; Thermo Fisher Scientific, mixed effects models. Random effects were interquartile ranges (IQRs; 25th–75th per­ Waltham, MA, USA) (Herner et al. 2006). estimated at the subject level, nested within centile) to allow strengths of association for We focused our analyses of exposure–response seasonal phase and community, to account different pollutants to be compared by limit­ relationships on key transition metals that can for correlated within­individual repeated ing differences due to units of measurement or generate reactive oxygen species by Fenton­ measures. To focus estimates of associations concentration range. type reactions: vanadium (V), chromium (Cr), at the subject level, we adjusted for between­ We evaluated the covariance structure iron (Fe), nickel (Ni), copper (Cu), manganese community and between­phase exposure using empirical variograms and found models (Mn), lead (Pb), and zinc (Zn). effects as proposed by Janes et al. (2008) by were best fit as an autoregressive­ 1 correla­ The second composited quarter was ana­ using exposures that were meanc­entered across tion structure. We performed residual analy­ lyzed for WSOC using a General Electric community and phase [see Supplemental ses to examine deviations from standard linear Sievers Total Organic Carbon Analyzer (GE Analytical Instruments, Boulder, CO, USA). Table 3. Exposure correlation matrix for outdoor PM0.25 mass and organic components. The remaining composited half was PAH analyzed for organic tracer compounds Pollutant WSOC Total LMW MMW HMW Hopanes n-Alkanes Organic acids by GC/MS along with field blanks, labora­ tory blanks, spiked samples, and standard PM0.25 mass 0.25 0.45 0.44 0.38 0.39 0.31 0.17 –0.18 WSOC 1.00 0.39 0.41 0.29 0.40 0.31 0.15 0.09 reference material (Urban Dust Standard PAHs Resource Material 1649a; National Institute Total 1.00 0.89 0.93 0.81 0.54 0.15 –0.19 of Standards and Technology, Gaithersburg, LMW 1.00 0.79 0.66 0.63 0.24 –0.24 MD, USA). Spike recovery after correction for MMW 1.00 0.67 0.51 0.12 –0.33 internal standard recoveries was in the range of HMW 1.00 0.41 0.20 –0.03 96–110% for PAHs, 99–104% for hopanes, Hopanes 1.00 0.08 –0.26 and 68–136% for n­alkanes. Blank concen ­ n-Alkanes 1.00 –0.06 trations of MMW PAHs, HMW PAHs, and All exposures are mean centered by study community and seasonal phase, and results are Spearman rank correlations. hopanes were below analytical detection lim­ its (~ 10 pg/m3 air). The method detection Table 4. Exposure correlation matrix for outdoor PAH and source apportioned mass. limits for remaining compounds were limited Vehicular Biomass Ship NSS by field and laboratory blanks. Uncertainties PAH emissions burning emissions SOAs RS dust sulfate Sea salt Unknown for each measurement were estimated based Total 0.71 0.22 0.10 0.19 0.24 0.06 0.33 0.33 on analytical uncertainties and uncertainties LMW 0.70 0.14 0.17 0.27 0.39 0.10 0.34 0.31 from the blank correction and were used to MMW 0.66 0.36 –0.01 0.04 0.19 –0.06 0.27 0.30 determine if each measurement was statisti­ HMW 0.66 0.08 0.09 0.27 0.13 0.13 0.19 0.14 cally different from zero. The precision of the Abbreviations: RS, resuspended; NSS, non-sea salt. All exposures are mean centered by study community and seasonal spike and standard reference material analyses phase, and results are Spearman rank correlations. Source apportioned mass data come from Arhami et al. (2010). Table 2. Descriptive statistics of outdoor measurements and indoor/outdoor (I/O) ratios of PM0.25 organic components and transition metals from 47 weeks of 5-day filter composites. Warm season Cool season Exposure Mean ± SD IQR Min/max I/O ratio Mean ± SD IQR Min/max I/O ratio IQR overalla Organic components PM0.25 mass (µg/m3) 9.51 ± 3.46 7.24 4.67/14.7 0.88 8.65 ± 4.51 6.07 3.31/19.3 0.94 7.37 WSOC (µg/m3)b 0.52 ± 0.23 0.31 0.08/1.01 0.95 0.38 ± 0.23 0.39 0.06/0.94 0.94 0.37 PAHs (ng/m3) Total 0.88 ± 0.37 0.47 0.40/1.75 0.84 1.04 ± 0.61 0.73 0.40/2.70 0.99 0.56 LMW 0.38 ± 0.15 0.20 0.19/0.74 0.78 0.33 ± 0.15 0.19 0.17/0.73 1.02 0.19 MMW 0.26 ± 0.12 0.18 0.09/0.50 0.85 0.35 ± 0.24 0.33 0.09/0.96 0.74 0.24 HMW 0.24 ± 0.11 0.18 0.11/0.50 0.97 0.37 ± 0.24 0.32 0.14/1.01 1.04 0.21 Hopanes (ng/m3) 0.27 ± 0.34 0.36 0.06/1.57 1.00 0.25 ± 0.25 0.35 0.06/0.83 0.97 0.35 n-Alkanes (ng/m3) 36.3 ± 23.5 43.2 9.9/81.2 1.39 54.8 ± 111 15.9 11.7/ 500 1.30 29.4 Organic acids (µg/m3) 0.22 ± 0.17 0.30 0.06/0.54 5.05 0.26 ± 0.22 0.26 0.07/0.96 1.24 0.29 Transition metals (ng/m3) V 4.83 ± 2.07 2.10 1.66/11.3 0.75 2.10 ± 1.19 2.40 0.54/4.25 0.77 2.95 Cr 10.2 ± 30.2 2.21 0.00/139 0.89 0.26 ± 0.45 0.49 0.00/1.24 1.00 1.18 Mn 3.09 ± 2.88 3.10 0.00/13.8 0.57 2.02 ± 1.43 1.76 0.27/6.19 0.70 2.24 Fe 144 ± 127 167 0.00/588 0.49 92.5 ± 64.2 74.7 9.39/287 0.74 115 Ni 7.21 ± 18.0 3.51 0.00/82.8 0.83 0.20 ± 0.61 0.816 0.00/1.44 2.27 1.64 Cu 6.45 ± 4.35 5.50 0.35/16.0 0.64 4.69 ± 3.22 4.91 0.43/11.3 0.60 4.69 Zn 6.88 ± 4.16 6.39 0.00/15.8 0.78 6.08 ± 3.51 4.81 1.75/13.0 0.93 5.77 Abbreviations: max, maximum; Min, minimum. aOverall IQR used in regression models to estimate expected change in the biomarker from exposure to the air pollutant. bWSOC (µg C/m3) was multiplied by 1.8 to yield mass of organic components (µg/m3) according to Turpin and Lim (2001). 758 118 | number 6 | June 2010 • Environmental Health Perspectives ovlume