Characterization of thermal decomposition of oxygenated organic compounds in FIGAERO-CIMS

Figures & data

Table 1. Chemical compounds tested in this study.

Type	Group	Compound	Molecular formula (MF)	O:C	H:C	OSC	OOA type
Alcohols	4	Xylitol	C5H12O5	1.00	2.40	–0.40	OOA
	4	Meso-Erythritol	C4H10O4	1.00	2.50	–0.50	LO-OOA
	4	Mannitol	C6H14O6	1.00	2.33	–0.33	OOA
Monoacids	–	Behenic acid	C22H44O2	0.09	2.00	–1.82	LO-OOA
	–	Stearic acid	C18H36O2	0.11	2.00	–1.78	LO-OOA
	–	Palmitic acid	C16H32O2	0.13	2.00	–1.75	LO-OOA
	–	Tridecanoic acid	C13H26O2	0.15	2.00	–1.69	LO-OOA
	–	Decanoic acid	C10H20O2	0.20	2.00	–1.60	LO-OOA
	–	Acetic acid	C2H4O2	1.00	2.00	0.00	MO-OOA
	–	Formic acid	CH2O2	2.00	2.00	2.00	MO-OOA
Diacids	–	Dodecanedioic acid	C12H22O4	0.33	1.83	–1.17	LO-OOA
	–	Sebacic acid	C10H18O4	0.4	1.8	–1	LO-OOA
	–	Azelaic acid	C9H16O4	0.44	1.78	–0.89	LO-OOA
	–	Suberic acid	C8H14O4	0.5	1.75	–0.75	LO-OOA
	1	Succinic acid	C4H6O4	1	1.5	0.5	MO-OOA
	–	Malonic acid	C3H4O4	1.33	1.33	1.33	MO-OOA
	–	Oxalic acid	C2H2O4	2	1	3	MO-OOA
Polyacids	3	1,3,5-Cyclohexanetricarboxylic acid	C9H12O6	0.67	1.33	0.00	MO-OOA
	3	Benzene-1,3,5-Tricarboxylic acid	C9H6O6	0.67	0.67	0.67	MO-OOA
	3	1,2,3,4-Butanetetracarboxylic acid	C8H10O8	1.00	1.25	0.75	MO-OOA
	3	Tricarballylic acid	C6H8O6	1.00	1.33	0.67	MO-OOA
Multifunctional	2	5-Oxoazelaic acid	C9H14O5	0.56	1.56	–0.44	OOA
	2	4-Oxoheptanedioic acid	C7H10O5	0.71	1.43	0	MO-OOA
	4	Sucrose	C12H22O11	0.92	1.83	0	MO-OOA
	2	1,3-Acetonedicarboxylic acid	C5H6O5	1	1.2	0.8	MO-OOA
	1	Oxaloacetic acid	C4H4O5	1.25	1	1.5	MO-OOA
	3	Citric acid	C6H8O7	1.17	1.33	1	MO-OOA
	1	Malic acid	C4H6O5	1.25	1.5	1	MO-OOA
	1	Tartaric acid	C4H6O6	1.5	1.5	1.5	MO-OOA

Note: The “Type” column defines the functionality of the compound. A subset of the chemicals is also categorized into four “Groups” (numbered as 1 to 4) to evaluate the effect of chemical structure on thermal decomposition behavior. All compounds are categorized into LO-OOA, OOA, or MO-OOA based on their OS_C, using the cutoff OS_C values reported in Ng et al. (2011).

Figure 1. Visualization of chemical structures of the compounds in each “Group” (Table 1). A: Succinic acid, B: Malic acid, C: Oxaloacetic acid, D: Tartaric acid, E: 5-Oxoazaleic acid, F: 4-Oxoheptanedioic acid, G: 1,3-Acetonedicarboxylic acid, H: Benzene-1,3,5-Tricarboxylic acid, I: 1,3,5-Cyclohexanetricarboxylic acid, J: Tricarballylic acid, K: 1,2,3,4-Butanetetracarboxylic acid, L: Citric acid, M: Meso-Erythritol, N: Xylitol, O: Mannitol, P: Sucrose.

Figure 2. All compounds tested plotted onto the Van Krevelen diagram. A compound with OS_C $\le$ –0.5 is categorized as LO-OOA and a compound with OS_C $\ge 0$ is categorized as MO-OOA. If a compound’s OS_C is –0.5 < OS_C < 0, the compound can be either LO-OOA or MO-OOA and is categorized as OOA.

Figure 3. Fraction of main species (decarboxylation product, dehydration product, parental compound, and other) after undergoing thermal desorption for compounds in each “Type” (functional group) (Table 1). For each type, the compounds are ordered in ascending O:C ratio. For each compound, the reported fraction value is the average of two experimental measurements. Note: Only one measurement is available for sucrose.

Figure 4. Measured number of carbon (measured nC), hydrogen (measured nH), and oxygen (measured nO) plotted against the true number of carbon (true nC), hydrogen (true nH), and oxygen (true nO). The solid line corresponds to a one-to-one line. The data points are color-coded according to the functional groups.

Figure 5. The scatter plots of various parameters including the nC, nO, nH, DBE, T_max, and MW color-coded with the degree of thermal decomposition. The fraction on the y-axis indicates the fraction of parental compound left upon heating and is divided into three categories: (1) minor thermal decomposition (parental compound left: 85–100%, blue), (2) considerable thermal decomposition (parental compound left: 40–50%, purple), and (3) significant thermal decomposition (parental compound left: 0–10%, red).

Table 2. Average effective MF and range of DBE, MW, nO, and T_max for compounds exhibiting three different degrees of thermal decomposition: minor, considerable, and significant.

Degree of thermal decomposition	Parameter	Range
Minor	DBE	0–7
	MW	46–341
	Tmax ($°$C)	18–141
	nO	2–6
	Avg. effective MF	C7.65H13.7O3.9
Considerable	DBE	3
	MW	146–192
	Tmax ($°$C)	72–111
	nO	5–7
	Avg. effective MF	C5.7H7.3O6
Significant	DBE	2–4
	MW	234–342
	Tmax ($°$C)	147–176
	nO	8–11
	Avg. effective MF	C10H16O9.5

Figure 6. Fraction of major species (decarboxylated product, dehydrated product, parental compound, and other) after undergoing thermal desorption for compounds in each “Group” (Table 1 and Figure 1). For each compound, the reported fraction value is the average of two experimental measurements. Note: Only one measurement is available for sucrose.

Figure 7. Fraction of parental compound detected by FIGAERO-CIMS after desorption process vs. the carbon oxidation state of polyacids. Note: succinic acid (diacid) is not classified as polyacid but added in this figure as it shows the effect of adding more acids to the diacid.

Figure 8. Van Krevelen diagrams of the average mass spectra of each OA factor resolved by PMF analysis of FIGAERO-CIMS data acquired at a field campaign in Yorkville, GA (Chen et al. 2020). The data points are colored by T_max. The five factors are daytime more oxidized (Day-MO), daytime organic-nitrate-rich (Day-ONRich), morning less oxidized (MRN-LO), afternoon less oxidized (AFTN-LO), and nighttime organic-nitrate-rich (NGT-ONRich).

Figure 9. Fraction of four species (C₆H₈O₇ (parental compounds denoted as M), C₆H₆O₆ (primary dehydration product), C₆H₄O₅ (secondary dehydration product), and C₅H₆O₄ (decarboxylation product of primary dehydration product)) for ramping rate of 3.3 $°$C min⁻¹, 13.3 $°$C min⁻¹, and 40 $°$C min⁻¹.

Figure 10. Thermal desorption profiles (thermograms) of citric acid for ramping rate of (a) 40 $°$C min⁻¹, (b) 13.3 $°$C min⁻¹, and (c) 3.3 $°$ C min⁻¹.

Table 3. T_max of citric acid (C₆H₈O₇), its primary dehydration product (C₆H₆O₆), secondary dehydration product (C₆H₄O₅), and decarboxylation product of its primary dehydration product (C₅H₆O₄).

Ramping rate $(°$C min^–1)	C6H8O7 Tmax (°C)	C6H6O6 Tmax (°C)	C6H4O5 Tmax (°C)	C5H6O4 Tmax (°C)
40	118 $\pm$ 4	151 $\pm$ 3	164 $\pm$ 7	172 $\pm$ 3
13.3	113 $\pm$ 3	146 $\pm$ 11	159 $\pm$ 3	173 $\pm$ 2
3.3	106 $\pm$ 2	137 $\pm$ 2	140 $\pm$ 2	–

Note: The uncertainty corresponds to standard deviations of two distinctive measurements.

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