Differences in the OC/EC Ratios that Characterize Ambient and Source Aerosols due to Thermal-Optical Analysis

Figures & data

FIG. 1 Typical NIOSH TOT thermogram. The split point is determined from the laser absorbance in the He-Ox phase to the initial absorbance in the He phase (designated as horizontal dashed line). Char production is defined by attenuation of the laser signal and char evolution defined by the increase in the laser signal prior to EC evolution. FID1 (solid line)–-carbon species at 100% signal, FID2 (dotted line)–-carbon species at 25% signal, laser transmission (solid line), and temperature protocol (dashed line) (color figure available onlne).

TABLE 1 Temperature protocols for the 3 methods

		NIST-EPA			NIOSH			IMPROVE
Step	Atm.	Temp. (°C)	RT (s)	Ramp Rate (°C/s)	Temp. (°C)	RT (s)	Ramp Rate (°C/s)	Temp. (°C)	Est. RT (s)*	Avg. Ramp Rate (°C/s) ^†
OC1	He	200	60	3	310	70	4	120	120	1
OC2	He	400	60	7	475	60	8	250	120	2
OC3	He	600	60	10	615	60	10	450	120	3
OC4	He	785	150	5	870	105	8	550	120	4
Cool	He	550	60	9	550	60	9	550	120	4
EC1	He-Ox	620	60	10	625	60	10	700	120	5
EC2	He-Ox	690	45	15	700	60	12	850	120	6
EC3	He-Ox	760	45	17	775	60	13
EC4	He-Ox	830	45	18	890	110	8
EC5	He-Ox	900	90	10

TABLE 2 Total carbon measurements for NIST-EPA, NIOSH, and IMPROVE protocols. There was no difference for TC between TOT and TOR for the individual protocols

Method	Average ± SD	Range	Method	Average ± SD	Range
Sample type	(μg/cm^2)	(μg/cm^2)	Sample type	(μg/cm^2)	(μg/cm^2)
Cookstove NIST-EPA	35.93 ± 30.25	4.65–109.78	Rural NIST-EPA	11.00 ± 6.34	2.90–36.07
Cookstove NIOSH	35.56 ± 30.04	4.61–106.19	Rural NIOSH	10.86 ± 6.40	2.93–35.62
Cookstove IMPROVE	36.30 ± 31.32	3.74–112.87	Rural IMPROVE	10.48 ± 6.43	2.47–35.46
Diesel NIST-EPA	26.05 ± 7.70	9.72–43.09	Urban NIST-EPA	79.60 ± 39.74	32.02–156.37
Diesel NIOSH	26.91 ± 7.91	12.18–44.41	Urban NIOSH	80.18 ± 42.07	32.04–163.08
Diesel IMPROVE	26.69 ± 7.76	10.19–44.27	Urban IMPROVE	82.19 ± 43.00	32.07–174.25

TABLE 3 Cookstove/fuel/phase combinations

No	Cookstove	Fuel	WBT phase*
1	Open fire (3-stone)	Kiln-dried Douglas fir	S
2	GTZ	Charcoal	H S
3	Philips	Kiln-dried Douglas fir	C H S
4	Philips	Seasoned oak	C H S
5	UCODEA rocket	Seasoned oak	C H S
6	UCODEA rocket	Charcoal	H S
7	VITA	Kiln-dried Douglas fir	C S
8	VITA	Seasoned oak	S
9	WFP rocket	Kiln-dried Douglas fir	C H S
10	WFP rocket	Seasoned oak	C H S

TABLE 4 The percent range and average OC/EC ratios for the 3 temperature protocols using optical transmission (TOT) and reflectance (TOR) for char correction. The optical (p value) t-test statistic compares between TOT and TOR for each protocol for each sample type. The thermal (p value) ANOVA-test statistic compares the different temperature protocols within an optical correction method (transmission or reflection). The p values <.05 are significantly different (shown in bold).

	TOT		TOR
Method Sample type	Average ± SD	Range	Average ± SD	Range	Avg. TOT/TOR	Optical (p value)
Cookstove NIST-EPA	2.29 ± 2.68	0.28–12.80	1.34 ± 1.15	0.29–5.39	1.71	.1512
Cookstove NIOSH	2.59 ± 3.20	0.24–15.33	1.86 ± 2.00	0.19–9.13	1.39	.1143
Cookstove IMPROVE	1.73 ± 2.17	0.24–11.62	1.26 ± 1.43	0.23–6.67	1.37	.0346
Thermal (p value)	.7772		.2696
Diesel NIST-EPA	2.16 ± 3.87	0.24–22.58	2.06 ± 3.91	0.13–22.58	1.05	.3165
Diesel NIOSH	1.54 ± 2.12	0.27–12.79	1.44 ± 2.16	0.17–12.78	1.07	.3024
Diesel IMPROVE	0.46 ± 0.22	0.10–0.97	0.37 ± 0.25	0.12–0.99	1.24	.0091
Thermal (p value)	.0001		.0001
Rural NIST-EPA	17.68 ± 12.86	2.61–84.43	10.83 ± 21.41	1.63–31.04	1.63	.0001
Rural NIOSH	17.67 ±10.09	3.48–58.16	7.92 ± 4.85	3.88–31.03	2.23	.0001
Rural IMPROVE	13.97 ± 6.21	1.70–25.71	6.48 ± 3.80	1.17–21.70	2.16	.0001
Thermal (p value)	.2230		.2460
Urban NIST-EPA	2.85 ± 0.77	1.41–4.47	2.54 ± 0.74	1.27–4.40	1.12	.2010
Urban NIOSH	2.99 ± 0.76	1.84–5.25	2.79 ± 0.90	1.46–4.75	1.07	.3307
Urban IMPROVE	1.69 ± 0.42	1.05–2.60	2.11 ± 0.65	1.18–3.57	0.80	.0175
Thermal (p value)	.0001		.0293

TABLE 5 The percent range and average EC/TC ratios for the 3 temperature protocols using optical transmission (TOT) and reflectance (TOR) for char correction. The optical (p value) t-test statistic compares between TOT and TOR for each protocol for each sample type. The thermal (p value) ANOVA-test statistic compares the different temperature protocols within an optical correction method (transmission or reflection). The p values <.05 are significantly different (shown in bold)

	TOT		TOR
Method Sample type	Average ± SD	Range	Average ± SD	Range	Optical (p value)
Cookstove NIST-EPA	0.34 ± 0.23	0.00–0.78	0.43 ± 0.21	0.00–0.78	.0391
Cookstove NIOSH	0.34 ± 0.24	0.00–0.78	0.41 ± 0.21	0.00–0.75	.1724
Cookstove IMPROVE	0.39 ±0.24	0.00–0.80	0.50 ± 0.21	0.00–0.83	.0690
Thermal (p value)	.2583		.293
Diesel NIST-EPA	0.48 ± 0.20	0.04–0.80	0.52 ± 0.24	0.04–0.88	.3165
Diesel NIOSH	0.51 ± 0.18	0.07–0.79	0.55 ± 0.21	0.07–0.85	.3024
Diesel IMPROVE	0.70 ± 0.09	0.51–0.91	0.75 ± 0.11	0.50–0.89	.0091
Thermal (p value)	.0001		.0001
Rural NIST-EPA	0.07 ± 0.04	0.00–0.28	0.14 ± 0.06	0.01–0.38	.0001
Rural NIOSH	0.07 ± 0.03	0.02–0.12	0.13 ± 0.05	0.00–0.24	.0001
Rural IMPROVE	0.08 ± 0.05	0.00–0.37	0.16 ± 0.07	0.00–0.46	.0001
Thermal (p value)	.0637		.0587
Urban NIST-EPA	0.27 ± 0.06	0.28–0.49	0.29 ± 0.06	0.21–0.46	.2010
Urban NIOSH	0.26 ± 0.04	0.18–0.42	0.28 ± 0.07	0.19–0.44	.3307
Urban IMPROVE	0.38 ± 0.06	0.16–0.35	0.33 ± 0.06	0.17–0.41	.0175
Thermal (p value)	.0001		.0293

FIG. 2 EC/TC ratios for the different cookstove/fuel/WBT combinations for the conventional methods (NIST-TOT, NIOSH TOT, and IMPROVE TOR) (color figure available onlne).

Bailis , R. , Ogle , D. , Still , D. , Smith , K. R. and Edwards , R. 2004 . The Water Boiling Test (WBT), Version 1.5 , Berkeley , California : University of California, Berkeley .

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