Evaluation of assumptions for estimating chemical light extinction at U.S. national parks

Figures & data

Table 1. Site locations and sample periods

Site	Abbreviation	State	Latitude	Longitude	Altitude (m ASL)	Sample period
Great Smoky Mountains NP^a	GRSM (S)	TN	35.6344	–83.9416	810	7/19/2006–8/17/2006
Great Smoky Mountains NP	GRSM (W)	TN	35.6344	–83.9416	810	1/11/2008–2/9/2008
Mount Rainier NP	MORA	WA	46.7583	–122.1244	434	8/1/2009–8/30/2009
Acadia NP^b	ACAD	ME	44.3771	–68.2610	157	8/1/2011–8/30/2011

Notes: ^aNP, national park. ^bThis study was conducted in Acadia NP on the Schoodic Peninsula 18 km east of the IMPROVE site at Winter Harbor.

Table 2. Average field blank and backup (where applicable) filter OC and WSOC concentrations (µg/sample)

	GRSM (S)^a	GRSM (W)^b	MORA^c	ACAD^d
Field blank OC	26	31	25	12.5
Backup filer OC	—	—	40	40
Average front filter OC	177	107	329	134
Field blank WSOC	280	389	29	8.2
Backup filter WSOC	—	—	45	25
Average front filter WSOC	4380	1320	266	112

Notes: ^aOC measured on front quartz fiber filters; WSOC measured on Zefluor and TIGF filters.

^bOC measured on front quartz fiber filters; WSOC measured TIGF filters.

^cOC and WSOC measured on front and backup quartz fiber filters.

^dOC and WSOC measured on front and backup quartz fiber filters.

Table 3. Average concentrations (µg/m³) during four field studies at three U.S. national parks

	GRSM (S)			GRSM (W)			MORA			ACAD
OM^a	5.2^b	5.4^c	3.4^d	1.9	2.1	2.1	3.3	3.9	3.4	1.5	1.4	1.6
EC	0.51	0.51	0.34	0.25	0.29	0.30	0.23	0.26	0.25	0.16	0.16	0.14
SO4^2-	9.0	7.7	6.4	1.8	1.3	1.3	1.1	1.2	1.1	0.98	0.97	1.2
NO3^-	0.043	0.047	0.12	0.76	0.63	0.80	0.040	0.033	0.17	0.17	0.064	0.13
NH4^+	1.9	1.8	—	0.80	0.67	—	0.37	0.38	—	0.24	0.22	—

Notes: ^aOM assumed to be 1.8OC.

^bAverage for all samples during this study.

^cAverage for samples with corresponding IMPROVE samples.

^dAverage for corresponding IMPROVE samples.

Figure 1. Average concentrations of OM (1.8OC), EC, sulfate, nitrate, and ammonium at GRSM (S), GRSM (W), MORA, and ACAD.

Table 4. Average molar ratios of NH₄⁺ to SO₄^2- during the four studies

	NH4^+a/SO4^2-	NH4^+b/SO4^2-
Site	(molar ratio)	(molar ratio)	Sulfate neutralization
GRSM (S)	1.16 ± 0.21	1.17 ± 0.22	Acidic
GRSM (W)	1.76 ± 0.56	2.4 ± 0.8	Neutralized
MORA	1.80 ± 0.31	1.86 ± 0.30	Neutralized
ACAD	1.00 ± 0.82	1.26 ± 0.51	Acidic

Notes: ^aAssuming NO₃^- was present as NH₄NO₃. NH₄⁺ was corrected by subtracting the amount of NH₄⁺ equivalent to NO₃^- from the measured NH₄⁺.

^bAssuming that all NH₄⁺ was associated with SO₄^2- and that NO₃- was associated with other cations.

Table 5. Measurements of the WSOC/OC ratio in previous studies and in this study

Study	Location	Site Type	Artifact Correction	WSOC/OC (%)
Zappoli et al. (1999)	Aspvreten, Sweden	Background	No	77
Kiss et al. (2002)	K-puszta, Hungary	Rural	No	71
Miyazaki et al. (2006)	Tokyo, Japan	Urban	Yes	20–35
Sullivan and Webber (2006)	Atlanta, GA	Urban	No	42–47
Hallar et al. (2013)	Storm Peak Lab, CO	Remote	Yes	89
This study	GRSM (S)	Rural	No	22
This study	GRSM (W)	Rural	No	21
This study	MORA	Remote	Yes	77
This study	ACAD	Remote	Yes	93

Table 6. The frequency of detection (percent of sample periods) of alternative hydration states

	Particle diameter (µm)
	0.025		0.05		0.1		0.2		0.4		Total
Study	MH	LH	MH	LH	MH	LH	MH	LH	MH	LH	MH	LH
GRSM (S)	15	—^a	10	—	16	—	13	—	7	—	12	—
GRSM (W)	33	17	33	17	33	17	33	17	33	17	33	17
MORA	4	—	5	—	5	—	5	—	4	—	5	—
ACAD	—	—	—	—	—	—	—	—	—	—	<1	—

Notes: MH and LH indicated more hydrated and less hydrated states, respectively. ^aDash indicates that the hydrated state was observed with zero frequency.

Table 7. Average OM/OC ratios in DCM and water extracts during the four studies

			Weighted	WSOC
Site	DCM	Water	average	recovery (%)
GRSM (S)	1.9 ± 0.3	2.4 ± 0.3	2.0 ± 0.3	46 ± 22
GRSM (W)	2.8 ± 0.2	2.4 ± 0.5	2.7 ± 0.3	100 ± 17
MORA	2.1 ± 0.1	2.1 ± 0.2	2.1 ± 0.2	90 ± 13
ACAD	1.8 ± 0.2	2.3 ± 0.1	2.2 ± 0.2	60 ± 7

Figure 2. Hygroscopic growth factors from high to low RH (crystallization scan) at GRSM (S), GRSM (W), MORA, and ACAD.

Figure 3. Average dry size distributions during the four studies. Individual size distributions were normalized to the total number concentration before averaging.

Figure 4. Distribution of modal peaks in SMPS size distributions during the four studies.

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