The Impact of Deliquescence and pH on Cr Speciation in Ambient PM Samples

Figures & data

TABLE 1 Average mass of sampled PM and spiked chromium isotopes in this work

Type	Mass (μg)
^50Cr(III)	0.0220
^53Cr(VI)	0.0088
TSP	1. × 10^3 ± 4.40 × 10^2
PM2.5	7.30 × 10^2 ± 2.5 × 10^2

TABLE 2 Deliquescence RH values for K₂Cr₂O₇, Cr(NO₃)₃, and sodium bicarbonate in this work

Type	T Temperature (°C)	% DRH
Cr (NO3)3	25 ± 1	52 ± 1
K2Cr2O7	26 ± 1	94 ± 1
Sodium bicarbonate	25 ± 1	91 ± 1

TABLE 3 HPLC-ICP-MS operating conditions

	Dionex IonPac CS5A
Column	(250 × 4.0 mm, 5 mm)
Injection volume	100 μL
Flow rate	1.4 mL min^−1
Gradient elution	0.6 to 1.2 M HNO3
Forward power	1400 W
Cool argon gas	13 L min^−1
Auxiliary argon gas	0.85 L min^−1
Nebulizer argon gas	0.89 L min^−1
Data acquisition mode	PlasmaLab Transient Time Resolved Analysis (TRA)
Dwell time	200 ms
Transient acquisition time	300 s
Cones	Xs
Torch	Quartz glass with screen location
Nebulizer	Glass concentric
Spray chamber	Glass impact bead
CCT gas	7% H2 in He (4–6 mL min^−1)
Target isotopes	^50Cr, ^52Cr, ^53Cr
Instrument tuning	Natural abundance In (NO3)3

TABLE 4 Elemental and organic carbon concentrations in ambient PM

Element	Concentration (ng/m^3)	Standard deviation (ng/m^3)
Mg	392.61	363
Al	281.16	175
K	205.79	83.6
Ca	1087.17	922
Cr	21.7	18.3
Mn	11.96	9.76
Fe	390.4	331
Co	0.23	0.23
Ni	27.75	18.3
Cu	9.03	3.97
Zn	15.53	7.2
As	0.43	0.26
Se	0.42	0.23
Sr	2.47	2.26
Ag	1.37	1.71
Cd	0.15	0.044
Sb	0.07	0.042
Ba	4.60	2.57
Tl	0.1	0.05
Pb	4.16	1.4
U	0.32	0.19
OC	4980	781
EC	21.73	30.4

FIG. 1 Water uptake by PM_2.5 at 25°C and different RH values.

FIG. 2 The loss of Cr(VI) at acidic and basic pH and different RH values.

FIG. 3 The conversion of Cr(III) to Cr(VI) at acidic and basic pH and different RH values.