Table 2.

Median concentrations of water-soluble metals and total organics in ambient fine particles and their corresponding DTT solution concentrations and DTT responses.

Species	Median Particulate Concentration (ng m−3-air)	Concentration Relative to PQNa		Concentration Referenceb	Median Concentration in DTT solution (μM)	DTT Response (μM min−1)
		Mass Basis	Mole Basis
Water-Soluble Metals
Fe	7.0	23	84	c	1.37	0.062
Mn	2.0	6.5	24	c	0.40	0.39
Cu	1.9	6.1	20	c	0.33	0.65
V	0.55	1.8	7.2	c	0.12	0.012
Ni	0.50	1.6	5.7	c	0.093	0.010
Pb	3.8	12	12	c	0.20	0.013
Co	0.035	0.1	0.4	c	0.0065	0.0017
Quinones and PHEN
BQN	0.63	2.0	3.9	d	0.064	0.0081
PQN	0.31	1	1	e	0.017	0.23
1,4-NQN	0.11	0.4	0.5	e	0.0077	0.0041
1,2-NQN	0.02	0.1	0.08	e	0.0012	0.0049
PHEN	0.7	2.3	2.6	f	0.043	0.0033

^aEach concentration was divided by the concentration of PQN, either on a mass basis (ng m⁻³-air) or a mole basis (nmol m⁻³-air). The mole basis relative concentrations are most relevant here since our DTT results are expressed using species concentrations on a molar basis (e.g., Table 1).

^bAs described in Sect. S2 of the Supplement, we examined multiple studies to determine typical particulate concentrations of each species. The reference listed in this column is the study that contained the median average value for a given species. Concentrations in the DTT solution were determined assuming that 32.8 m³ of air was sampled onto a filter and the whole filter PM mass was added to 3.0 mL of DTT reaction solution.

^cConnell et al. (2006) for PM_2.5 collected in Steubenville, Ohio during 2000–2002.

^dDelhomme et al. (2008) for PM_2.5 collected in Tempe, Arizona during 2005.

^eCho et al. (2004) for PM_2.5 collected in Riverside, California in May through July 2001.

^fThe maximum PHEN concentration reported for PM_2.5 (range: 0.043 to 0.7 ng m⁻³) in Atlanta, GA and Missoula, MT during January to April (Ward et al., 2005; Li et al., 2009b).