Aerosol Inorganic Composition at a Tropical Site: Discrepancies Between Filter-Based Sampling and a Semi-Continuous Method

Figures & data

TABLE 1 Overview of aerosol samplers and analytical techniques employed for the measurement of the aerosol species NH₄ ⁺, NO₃ ⁻, Cl⁻, and SO₄ ²⁻ at FNS during LBA-SMOCC 2002

Abbreviation	Sampler	Sampling height	Institution*	Analyses
WAD/SJAC	Wet-annular denuder/Steam-Jet Aerosol Collector (PM2.5 or TSP)	5.3 m	MPI-C	NH4 ^+ (FIA), NO3 ^−, Cl^−, and SO4 ^2− (IC), on-line (Trebs et al. 2004)
DFP	Denuder-filterpack (PM2.5 or TSP)	5.3 m	UPR—ITES, MPI-C	NH4 ^+, NO3 ^−, Cl^−, and SO4 ^2−(IC)
SFU	Stacked filter units (PM2.5 and PM10)	4 m	USP, WIS, UGent	NH4 ^+, NO3 ^−, Cl^−, and SO4 ^2− (IC), elemental S (PIXE)
HiVol	HiVol sampler (PM2.5 only)	1.8 m	UGent, WIS	NH4 ^+, NO3 ^−, Cl^−, and SO4 ^2− (IC)
UPR—ITES: University of Puerto Rico—Institute for Tropical Ecosystem Studies (San Juan, Puerto Rico).
USP: University of São Paulo (Brazil).
WIS: Weizmann Institute of Science (Rehovot, Israel).
UGent: Ghent University (Belgium).

TABLE 2 Filter blanks of the aerosol species NH₄ ⁺, NO₃ ⁻, Cl⁻, and SO₄ ²⁻ expressed as average percentage [%] of typically observed concentrations at FNS during LBA-SMOCC 2002

Blanks	NH4 ^+[%]	NO3 ^−[%]	Cl^−[%]	SO4 ^2−[%]
DFP-Teflon	28	33	8	21
SFU-IC	5	15	35	15
SFU-PIXE	—	—	—	50
HiVol	10	10	—	10

FIG. 1 Box-and-whisker plots showing statistical distributions of concentrations during daytime (D) and nighttime (N) for aerosol ions (a) NH₄ ⁺, (b) NO₃ ⁻, (c) Cl⁻, and (d) SO₄ ²⁻ measured with the WAD/SJAC, DFP (Teflon filters), SFU (polycarbonate filters), and HiVol sampler (quartz-fiber filters) during the dry (biomass burning) season (12–23 Sep.) at FNS during LBA-SMOCC 2002 (HiVol samples were analyzed for PM_2.5 only, elemental S is presented as SO₄ ²⁻ equivalent assuming that the measured S concentration is entirely attributable to aerosol SO₄ ²⁻).

TABLE 3 Summary of results (median, 25th percentile and 75th percentile of all samples) for aerosol ions NH₄ ⁺, NO₃ ⁻, Cl⁻, and SO₄ ²⁻ measured with the WAD/SJAC, DFP, SFU and HiVol sampler during the transition period (07–31 Oct) and the onset of the wet season (01–14 Nov) at FNS during LBA-SMOCC 2002

		NH4 ^+ (ng m^−3)			NO3 ^− (ng m^−3)			Cl^− (ng m^−3)			SO4 ^2− (ng m^−3)			S ^(3) (PIXE) (ng m^−3)
Season	Sampler	m	P 0.25	P 0.75	m	P 0.25	P 0.75	m	P 0.25	P 0.75	m	P 0.25	P 0.75	m	P 0.25	P 0.75
Transition period	WAD/SJAC	409.3	242.1	553.0	217.4	174.7	340.5	33.9	27.7	46.3	457.3	366.4	596.4	—	—	—
	DFP ^(1)	247.3	144.5	411.6	166.0	130.0	327.3	13.7	7.9	20.9	647.2	603.7	866.4	—	—	—
	SFU	470.6	136.2	796.2	187.6	105.2	314.1	20.5	13.7	25.8	889.5	371.6	1572.4	1036.6	329.9	1835.4
	HiVol ^(2)	854.3	817.0	888.0	182.1	71.0	525.6	15.4	12.9	17.5	1383.4	1376.1	1444.8	—	—	—
Wet season	WAD/SJAC	340.3	259.8	367.9	135.4	120.3	165.0	48.6	27.8	57.8	411.0	282.2	551.8	—	—	—
	DFP	30.5	18.5	59.9	< LOD	< LOD	< LOD	25.7	13.9	124.2	136.3	118.9	138.0	—	—	—
	SFU	189.7	166.1	219.3	60.4	9.4	67.2	7.4	4.2	9.8	349.6	311.3	372.5	349.9	333.9	395.4
	HiVol	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—

FIG. 2 Average relative differences (assuming the WAD/SJAC is the reference) between the mean of concentrations determined from integrating samplers (DFP, SFU, and HiVol) and concentrations measured with the WAD/SJAC for the dry season (day- and nighttime), transition period and wet season at FNS during LBA-SMOCC 2002. Error bars indicate standard deviations of differences.

TABLE 4 Correlation coefficients (r²) and reduced major axis analysis (RMA) regression results (Y = (A ± σ_A) + (B ± σ_B)*X, where σ_A and σ_B are the standard errors of intercept A and slope B, respectively) for WAD/SJAC, DFP, SFU, and HiVol samplers. Correlations for the DFP sampler refer only to concentrations determined on the Teflon filters. Results are shown for (a) the late dry (biomass burning) season (day-and nighttime listed separately); (b) the transition period and the onset of the wet season (clean conditions) at FNS during LBA-SMOCC 2002 (fields were left empty if values were smaller than the limit of detection or N < 3)

(a)
		Dry season-DAY				Dry season-NIGHT
Combination			A ± σ A	B ± σ B			A ± σ A	B ± σ B
X − Y	Compound	r^2	[ng m^− 3]	[1]	N	r^2	[ng m^− 3]	[1]	N
WAD/SJAC-DFP	Aerosol NH4 ^+	—	—	—	—	0.62	986 ± 659	1.5 ± 0.5	3
WAD/SJAC-SFU		0.25	−549 ± 743	1.9 ± 0.7	5	0.01	−490 ± 972	2.6 ± 1.0	6
WAD/SJAC-HiVol		0.30	403 ± 800	2.1 ± 0.8	5	0.01	−326 ± 879	2.3 ± 0.9	6
SFU-HiVol		0.10	375 ± 911	1.7 ± 0.7	5	0.99	118.9 ± 79	0.9 ± 0.04	6
WAD/SJAC-DFP	Aerosol NO3 ^−	—	—	—	—	0.88	2044 ± 433	1.2 ± 0.2	3
WAD/SJAC-SFU		0.33	−126 ± 257	0.6 ± 0.2	5	0.01	−897 ± 564	1.2 ± 0.4	7
WAD/SJAC-HiVol		0.01	−501 ± 1489	3.0 ± 1.4	5	0.01	−839 ± 312	0.6 ± 0.2	6
SFU-HiVol		0.35	96 ± 1035	4.8 ± 1.7	5	0.88	152 ± 50	0.5 ± 0.07	6
WAD/SJAC-DFP	Aerosol Cl^−	—	—	—	—	0.85	33 ± 34	0.9 ± 0.2	3
WAD/SJAC-SFU		0.40	−3 ± 9	0.2 ± 0.1	4	0.69	−0.2 ± 11	0.5 ± 0.1	5
WAD/SJAC-HiVol		0.77	−147 ± 88	3.6 ± 0.8	5	0.34	7 ± 5	0.1 ± 0.04	6
SFU-HiVol		0.58	−65 ± 117	18 ± 5.9	4	0.01	9 ± 5	0.2 ± 0.1	4
WAD/SJAC-DFP	Aerosol SO4 ^2−	—	—	—	—	0.03	433 ± 1554	2.1 ± 1.2	3
WAD/SJAC-SFU		0.40	−989 ± 870	2.9 ± 0.7	5	0.23	−110 ± 1146	2.6 ± 0.9	6
WAD/SJAC-HiVol		0.50	171 ± 910	2.2 ± 0.7	5	0.34	2163 ± 1752	4.2 ± 1.4	6
SFU-HiVol		0.01	1125 ± 887	0.83 ± 0.36	5	0.91	−1981 ± 608	1.6 ± 0.2	6
SFU(IC)-SFU(PIXE)		0.95	−46 ± 292	1.2 ± 0.12	5	0.98	−1992 ± 309	1.9 ± 0.1	6
(b)
		Transition period				Wet season
Combination			A ± σ A	B ± σ B			A ± σ A	B ± σ B
X − Y	Compound	r^2	[ng m^− 3]	[1]	N	r^2	[ng m^− 3]	[1]	N
WAD/SJAC-DFP	Aerosol NH4 ^+	0.18	−145 ± 150	1.1 ± 0.4	7	0.01	−373 ± 258	1.3 ± 0.7	3
WAD/SJAC-SFU		0.19	−449 ± 353	2.1 ± 0.8	6	0.89	169 ± 10	0.18 ± 0.1	3
WAD/SJAC-HiVol		0.68	10 ± 196	1.7 ± 0.4	5	—	—	—	—
SFU-HiVol		0.13	426 ± 196	0.8 ± 0.4		—	—	—	—
WAD/SJAC-DFP	Aerosol NO3 ^−	0.96	−356 ± 62	1.5 ± 0.1	5	—	—	—	—
WAD/SJAC-SFU		0.01	−91 ± 123	0.9 ± 0.4	6	0.02	−27 ± 81	1.0 ± 0.6	3
WAD/SJAC-HiVol		0.50	−209 ± 170	1.5 ± 0.5	5	—	—	—	—
SFU-HiVol		0.55	11 ± 99	1.4 ± 0.5	4	—	—	—	—
WAD/SJAC-DFP	Aerosol Cl^−	0.72	−16 ± 9	0.8 ± 0.2	4	—	—	—	—
WAD/SJAC-SFU		0.60	−11 ± 11	0.7 ± 0.3	4	0.04	4.6 ± 2.5	0.03 ± 0.02	3
WAD/SJAC-HiVol		0.29	1.8 ± 2.1	0.3 ± 0.1	4	—	—	—	—
SFU-HiVol		—	—	—	—	—	—	—	—
WAD/SJAC-DFP	Aerosol SO4 ^2−	0.47	−127 ± 235	1.6 ± 0.4	8	0.17	104 ± 14	0.06 ± 0.03	—
WAD/SJAC-SFU		0.65	−679 ± 445	2.6 ± 0.6	6	0.11	165 ± 98	0.5 ± 0.2	4
WAD/SJAC - HiVol		0.98	−119 ± 110	2.4 ± 0.9	5	—	—	—	—
SFU-HiVol		0.63	653 ± 322	0.9 ± 0.9	4	—	—	—	—
SFU(IC)-SFU(PIXE)		0.98	871 ± 59	1.1 ± 0.1	7	0.64	54 ± 71	0.9 ± 0.2	7

FIG. 3 Relative difference (%) (assuming the WAD/SJAC is the reference) between the concentrations of aerosol NH₄ ⁺ and SO₄ ²⁻ measured with SFU (polycarbonate filters) and WAD/SJAC for four days (D) and nights (N) during the dry (biomass burning) season (left Y-axis) along with the measured relative humidity (RH) (averages for respective sampling interval, right Y-axis) at FNS during LBA-SMOCC 2002.

FIG. 4 Absolute aerosol SO₄ ²⁻ difference between SFU (IC) and WAD/SJAC versus aerosol NH₄ ⁺ measured with the SFU sampler at FNS during LBA-SMOCC 2002. SO₂ measured with the WAD is plotted as aerosol SO₄ ²⁻ equivalent possibly formed on the filter. Linear regression was done with data from all seasons (N = 20). Error bars indicate measurement uncertainty.

FIG. 5 Relative difference (%) (assuming the WAD/SJAC is the reference) between the concentrations of aerosol NO₃ ⁻ and Cl⁻ measured with HiVol (quartz-fiber filters) and WAD/SJAC for four days (D) and nights (N) during the dry season (left Y-axis) along with gas phase concentrations (HNO₃ and HCl) (averages of respective sampling interval; measured with WAD; (right Y-axis)) at FNS during LBA-SMOCC 2002.

FIG. 6 Absolute aerosol SO₄ ²⁻ difference between SFU (PIXE) and SJAC versus aerosol K measured by PIXE at FNS during LBA-SMOCC 2002. Error bars indicate measurement uncertainty.

Trebs , I. , Meixner , F. X. , Slanina , J. , Oties , R. P. , Jongejan , P. and Andreae , M. O. 2004 . Real-time measurements of ammonia, acidic trace gases and water-soluble inorganic aerosol species at a rural site in the Amazon Basin . Atmospheric Chemistry and Physics , : 967 – 987 .

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