Black carbon emissions in gasoline vehicle exhaust: A measurement and instrument comparison

Figures & data

Figure 1. A schematic of the arrangement of the test vehicle, CVS tunnel, filter assemblies, and real-time BC measurement instruments used in this study.

Table 1. Details of the BC instrument properties used in this comparison study

Instrument name	Abbreviation	Manufacturer	Analyte	Operating principle	λ (nm)	Conversion factor	Data capture resolution	Intake flow rate (L/min)	Collection medium	Additional details
Thermal/Optical Carbon Analyzer model 2001	IMPROVE_A	Atmoslytic	EC	Thermal/optical	633	NA	300–1135 sec	60	Quartz fiber filter	IMPROVE_A Protocol
483 micro soot sensor	MSS	AVL	BC	Photoacoustic	808	0.27mg·m^−3 ·mV^−1	1 sec	1.9	In-Situ	NA
Rack Mounted aethalometer AE22	AE22	Magee Scientific	BC	Light attenuation	880	16 m^2·g^−1	5 sec	2.0	Quartz fiber tape	NA
Portable aethalometer AE51	AE51	Magee Scientific	BC	Light attenuation	880	16 m^2·g^−1	1 sec	0.10	Teflon coated glass fiber filter	NA
Sootscan model OT21 transmissometer	OT21_T	Magee Scientific	BC	Light attenuation	880	16 m^2·g^−1	300–1135 sec	60	Teflon filters	NA
Droplet PASS-1	PASS-1	Droplet Measurement Technologies	BC	Photoacoustic	781	4.7 m^2·g^−1	1 sec	1.0	In-situ	NA

Table 2. Details of the six vehicles and the corresponding number of tests used in the analyses

Vehicle	Model year	Injection system	No. of cycles	Engine displacement (L)	Emission category	Odometer reading (mi)	No. of FTP tests			No. of UC tests			No. of US06 tests			No. of ALT tests
							P2 Cert	E6	E10	P2 Cert	E6	E10	P2 Cert	E6	E10	P2 Cert
GDI-C1	2009	CGDI	6	3.0	ULEV II	2019	5	2	0	0	2	0	3	0	0	0
GDI-C2	2009	CGDI	8	4.4	ULEV II	293	6	10	0	1	1	0	0	0	0	0
GDI-W1	2010	WGDI	4	2.0	ULEV II	76	0	5	5	0	1	2	0	3	3	0
GDI-W2	2009	WGDI	6	3.8	LEV II	124,012	0	4	0	0	2	0	0	0	0	4
PFI1	2009	PFI	5	3.7	ULEV II	20,639	4	0	0	4	2	0	6	3	0	0
PFI2	2009	PFI	4	2.5	ULEV II	28,725	0	9	4	0	8	2	2	11	5	0
Notes: Cycles: FTP consists of Phase 1: cold start (505 sec, 5.78 km); Phase 2: transient (869 sec, 6.29 km), 10 = min hot soak; and Phase 3: hot start (505 sec, 5.78 km). The average speed, over the three phases is 34.1 km/hr. US06 consists of a single Phase 1: transient (600 sec, 13 km). The average speed is 77 km/hr. UC consists of Phase 1: cold start (300 sec, 1.9 km); Phase 2: transient (1135 sec, 13.8 km); 10=min hot soak; and Phase 3: hot start (300 sec, 1.9 km). The average speed, over the three phases is 39.6 km/hr.
Fuels: E6 is a 2009 Phase 3 commercial grade summer fuel containing 6% (by volume) ethanol. E10 is a 2010 Phase 3 commercial grade summer fuel containing 10% (by volume) ethanol. P2 Cert is a Phase 2 certification fuel containing MTBE.

Table 3. Test results, descriptive statistics, and MDLs for four BC measurement instrument

	Time integrated measurements		Real-time measurements
No. test	IMPROVE_A (mg/mi)	OT21_T (mg/mi)	MSS (mg/mi)	AE51 (mg/mi)
1	0.3541	0.2188	0.1608	0.1147
2	0.0068	−0.1264	0.0629	0.0160
3	0.1307	0.0000	0.0938	0.0232
4	0.1997	0.0968	0.1501	0.0900
5	0.0424	0.0328	No data	0.0452
Mean	0.1467	0.0444	0.1169	0.0578
SD	0.1807	0.1269	0.0465	0.0429
df	4	4	3	4
t 0.95	2.78	2.78	3.18	2.78
MDL	0.38	0.35	0.15	0.12
Notes: The ALT cycle consisted of (1) starting the vehicle; (2) accelerating the vehicle to 20 mph; (3) maintaining the speed at 20 mph for 5 min; (4) continuing driving at 20 mph for 20 min while collecting filter samples and making real-time BC measurements; (5) ending sampling and measuring; and then (6) decelerating and turning off the vehicle. The standard deviation (SD) for repeat measurements were calculated in mg/mi and detection limits were derived using the following equation: MDL (mass/mi) = SD(g/mi) × t(0.05, df), where t is the t score of the one-sided Student's t distribution, df is the number of degrees of freedom (N − 1), and 0.05 is the significance.

Table 4. Repeatability data for a) the time-integrated measurement methods OT21_T BC, IMPROVE_A EC, and PM mass and b) the real-time photoacoustic and light attenuation-based BC instruments

		PM				IMPROVE_A				OT21_T
No.	Combination	Mean (mg/mi)	SD (mg/mi)	RSD (%)	N	Mean (mg/mi)	SD (mg/mi)	RSD (%)	N	Mean (mg/mi)	SD (mg/mi)	RSD (%)	N
1	GDI_C1, FTP, P2 Cert	0.85	0.31	37	9	0.60	0.20	33	4	0.47	0.03	6.5	3
2	GDI_C1, US06, P2 Cert	3.02	2.94	97	4	0.69	0.26	38	2
3	GDI_C2, FTP, P2 Cert	1.48	0.47	32	7	0.96	0.43	45	3	1.04	0.88	84	2
4	GDI_C2, FTP, E6	3.10	1.18	38	12	2.59	0.95	37	6	1.93	0.24	12	2
5	PFI2, FTP, E6	0.49	0.25	51	8	0.37	0.09	24	2	0.39	0.24	61	5
6	PFI2, FTP, E10	0.35	0.21	59	5	0.38	0.39	102	3	1.16	0.12	11	2
7	PFI2, UC, E10	1.70	0.02	1.0	2	1.38	0.01	0.80	2
8	PFI2, US06, E6	0.58	0.25	44	3					0.42	0.23	55	2
9	PFI2, US06, E10	0.67	0.45	68	3	0.77	0.14	18	2
10	GDI_W2, FTP, E6	3.93	0.72	18	6	2.15	0.15	24	3	2.88	0.52	18	2
11	GDI_W2, U2, E6	10.74	0.31	2.93	2					8.45	0.24	5.0	2
12	PFI1, FTP, P2 Cert	0.42	0.21	50	4	0.45	0.30	67	2	0.37	0.13	36	3
13	PFI1, FTP, E6	0.99	0.38	39	4
14	PFI1, UC, P2 Cert	1.95	0.40	20	4	2.14	1.48	68	2	0.76	0.34	45	4
15	PFI1, UC, E6	2.61	0.95	36	3
16	PFI1, US06, P2 Cert	3.14	0.44	13	6	2.86	0.57	20	2	1.92	0.47	25	4
17	PFI1, US06, E6	7.66	2.04	27	3	5.48	1.22	22	2
18	GDI_W1, FTP, P2 Cert	1.22	0.02	1.56	2
19	GDI_W1, FTP, E6	1.78	0.28	16	10	1.46	0.19	13	6	1.94	0.25	13	2
20	GDI_W1, FTP, E10	1.29	0.72	56	4	1.46	0.45	31	2	1.63	0.44	27	2
21	GDI_W1, UC, E6	5.85	2.37	41	7	4.46	2.27	51	3	5.14	2.71	53	3
22	GDI_W1, UC, E10	4.74	0.41	8.7	2	3.44	0.15	4.2	2
23	GDI_W1, US06, P2 Cert	0.95	0.16	17	2
24	GDI_W1, US06, P2 Cert	1.70	0.64	38	12	1.12	0.22	20	5	1.27	0.23	18	5
25	GDI_W1, US06, E10	0.83	0.47	57	3	0.99	0.53	54	2
Pooled RSD		41%				41%				40%
(b)		MSS				AE51				AE22
No.	Combination	Mean (mg/mi)	SD (mg/mi)	RSD (%)	N	Mean (mg/mi)	SD (mg/mi)	RSD (%)	N	Mean (mg/mi)	SD (mg/mi)	RSD (%)	N
1	GDI_C1, FTP, P2 Cert	0.52	0.03	6.5	8	0.64	0.02	3.7	4	0.82	0.05	6.5	4
2	GDI_C1, US06, P2 Cert					0.27	0.10	38	2	0.41	0.36	86	3
3	GDI_C2, FTP, P2 Cert	0.85	0.49	58	4
4	GDI_C2, FTP, E6	2.19	0.25	11	6
5	PFI2, FTP, E6	0.27	0.07	28	5	0.30	0.08	28	4	0.38	0.13	35	5
6	PFI2, FTP, E10	0.27	0.06	21	4	0.40	0.24	61	3
7	PFI2, UC, E10
8	PFI2, US06, E6	0.37	0.10	26	3
9	PFI2, US06, E10	0.31	0.07	23	3
10	GDI_W2, FTP, E6	2.74	0.23	8.4	2
11	GDI_W2, UC, E6
12	PFI1, FTP, P2 Cert	0.37	0.06	16	4	0.39	0.06	15	3	0.54	0.05	10	3
13	PFI1, FTP, E6	0.63	0.25	39	3
14	PFI1, UC, P2 Cert	1.11	0.10	8.7	3	1.23	0.63	51	2	2.06	0.26	13	3
15	PFI1 UC, E6	1.96	0.03	1.5	2
16	PFI1, US06, P2 Cert	1.33	0.18	14	5	1.26	0.18	14	4	1.24	0.13	10	5
17	PFI1, US06, E6	3.61	0.94	26	2
18	GDI_W1, FTP, P2 Cert	1.02	0.12	12	2
19	GDI_W1, FTP, E6	1.50	0.31	20	6	1.33	0.30	22	3
20	GDI_W1, FTP, E10
21	GDI_W1, UC, E6	5.15	2.21	43	5
22	GDI_W1, UC, E10	3.60	0.30	8.2	2
23	GDI_W1, US06, P2 Cert	0.80	0.23	29	2
24	GDI_W1, US06, P2 Cert	0.94	0.11	12	7	0.66	0.22	34	2
25	GDI_W1, US06, E10	1.29	1.10	85	4
Pooled RSD		30%				31%				35%
Notes: Mean, SD, RSD, and N, represent the mean, standard deviation, relative standard deviation, and number of tests for each combination and method, respectively.

Figure 2. (a) Composite and (b) phase-by-phase emission rate comparison of MSS BC to IMPROVE_A EC.

Figure 3. (a) Composite and (b) Phase-by-phase emission rate comparison of AE51BC and IMPROVE_A EC.

Figure 4. (a) Composite and (b) phase-by-phase emission rate comparison of AE22 BC and IMPROVE_A EC.

Figure 5. (a) Composite and (b) phase-by-phase emission rate comparison of OT21_T BC and IMPROVE_A EC.

Table 5. The ratio of MSS BC to IMPROVE_A EC and its correlation to OC:EC as a function of a) driving cycle, and b) fuel type

(a) Driving cycle	Vehicle/fuel	No. of tests	Mean(BC:EC)	SD(BC:EC)	Mean(OC:EC)	Group mean(BC:EC) ± SD	Group mean(OC:EC) ± SD
FTP	GDI_C1/P2 Cert	3	1.08	0.28	1.79	1.03 ± 0.22	2.06 ± 1.43
	GDI_C2/P2 Cert	2	0.88	0.19	1.60
	GDI_C2/E6	2	1.04	0.15	0.57
	PFI2/E6	2	0.76	0.16	4.10
	PFI2/E10	3	1.27	0.76	4.13
	GDI_W2/E6	1	1.41	NA	1.51
	PFI1/P2Cert	2	1.11	0.65	3.34
	GDI_W1/E6	4	1.02	0.10	0.74
	GDI_W1/E10	1	0.73	NA	0.76
UC	PFI_2/E6	1	0.57	NA	2.37	1.03 ± 0.22	2.06 ± 1.43
	PFI_2/E10	1	0.52	NA	1.12
	PFI_1/P2 Cert	1	1.09	NA	1.58
	GDI_W1/E6	2	0.95	0.11	0.54
	GDI_W1/E10	2	1.04	0.04	0.55
US06	PFI2/E6	1	0.45	NA	0.98	0.84 ± 0.27	1.23 ± 0.77
	PFI2/E10	2	0.40	0.06	1.71
	PFI1/P2 Cert	2	0.46	0.01	0.22
	PFI1/E6	2	0.66	0.03	0.23
	GDI_W1/P2 Cert	1	0.62	NA	1.04
	GDI_W1/E6	3	0.80	0.08	0.47
	GDI_W1/E10	2	0.67	0.23	0.68
Note: SD denotes the sample standard deviation of the variables.
(b) Fuel	Vehicle/driving cycle	No. of tests	Mean(BC:EC)	SD(BC:EC)	Mean(OC:EC)	Group mean(BC:EC) ± SD	Group mean(OC:EC) ± SD
P2 Cert	GDI_C1/FTP	3	1.1	0.28	1.8	0.87 ± 0.28	1.6 ± 1.0
	GDI_C2/FTP	2	0.88	0.19	1.6
	PFI1/FTP	2	1.1	0.65	3.3
	PFI1/UC	1	1.1	NA	1.6
	PFI1/US06	2	0.46	0.01	0.22
	GDI_W1/US06	1	0.62	1.0	1.0
E6	GDI_C2/FTP	2	1.0	0.15	0.57	0.85 ± 0.29	1.3 ± 1.2
	PFI2/FTP	2	0.76	0.16	4.1
	PFI2/UC	1	0.57	NA	2.4
	PFI2/US06	1	0.45	NA	0.98
	GDI_W2/FTP	1	1.4	NA	1.5
	PFI1/US06	2	0.66	0.025	0.23
	GDI_W1/FTP	4	1.0	0.097	0.74
	GDI_W1/UC	2	0.95	0.11	0.54
	GDI_W1/US06	3	0.80	0.082	0.47
E10	PFI2/FTP	3	1.3	0.76	4.1	0.77 ± 0.33	1.5 ± 1.4
	PFI2/UC	1	0.52	NA	1.1
	PFI2/US06	2	0.40	0.06	1.7
	GDI_W1/FTP	1	0.73	NA	0.76
	GDI_W1/UC	2	1.0	0.04	0.55
	GDI_W1/US06	2	0.67	0.23	0.68

Table 6. Correlation between instruments for FTP tests where BC < 1.0 mg/mi

	R ^2 (95% CI)
Instrument	EC	MSS	PASS-1	AE51	AE22
EC
MSS	0.41 (0.00–0.80)
PASS-1	0.36 (0.00–0.98)	0.85 (0.44–0.97)
AE51	0.53 (0.00–0.96)	0.92 (0.73–0.98)	0.90 (0.47–0.99)
AE22	0.64 (0.00–0.95)	0.95 (0.81–0.99)	0.83 (0.33–0.97)	0.95 (0.81–0.99)
OT T	0.01 (0.00–0.94)	0.21 (0.00–0.77)	0.44 (0.00–0.87)	0.32 (0.00–0.80)	0.20 (0.00–0.71)

Figure 6. Composite emission rate comparison of PASS-1, AE51, and AE22 BC and MSS BC for FTP tests with BC <1.0 mg/mi.