Stable carbon isotopic compositions of low-molecular-weight dicarboxylic acids, glyoxylic acid and glyoxal in tropical aerosols: implications for photochemical processes of organic aerosols

Figures & data

Fig. 1 Map showing the location of the sampling site in Morogoro, Tanzania.

Fig. 2 Typical examples of 5-d backward air mass trajectories arriving at Morogoro during May to August 2011 sampling period.

Table 1. Stable carbon isotope ratios (δ¹³C, ‰) of dicarboxylic acids, glyoxylic acid and glyoxal in PM_2.5 aerosols collected from Tanzania, in July and August 2011

		Dicarboxylic acids
Date	Sample ID	Oxalic C2	Malonic C3	Succinic C4	Phthalic Ph	Glyoxylic acid ωC2	Glyoxal Gly
28/7	TAN01	−20.2	−18.7	−23.4	NA	NA	NA
29/7	TAN02	−15.9	−20.9	−20.6	−27.1	−29.5	−25.4
1/8	TAN03	−18.3	−18.8	−21.8	NA	−21.4	−19.9
2/8	TAN04	−18.1	−20.7	−22.5	NA	−22.6	−18.3
3/8	TAN05	−17.0	−18.9	−20.9	NA	−18.3	NA
4/8	TAN06	−16.9	−20.4	−16.8	−28.7	−24.0	−15.4
5/8	TAN07	−21.3	−18.8	−22.3	−28.2	−24.0	−25.6
6/8	TAN08	NA	−20.8	NA	NA	−24.0	NA
7/8	TAN09	−17.9	−18.8	−23.7	NA	−23.7	−19.2
8/8	TAN10	−18.6	−19.6	−24.0	NA	−17.6	−17.3
	Mean	−18.3	−19.6	−21.8	−27.5	−22.5	−20.2
	±SD	1.7	1.0	2.2	0.8	3.5	3.9

Analytical errors for δ¹³C are within 0.2‰.

NA: Not available.

Table 2. Stable carbon isotope ratios (δ¹³C, ‰) of dicarboxylic acids, glyoxylic acid and glyoxal in PM₁₀ aerosols collected from Tanzania, in May through August 2011

		Dicarboxylic acids
Date	Sample ID	Oxalic C2	Malonic C3	Succinic C4	Azelaic C9	Phthalic Ph	Glyoxylic acid ωC2	Glyoxal Gly
30/5	TAN11	−20.9	−21.9	−27.8		NA	−25.9	−30.5
31/5	TAN12	−23.3	−23.8	−21.5		NA	−29.3	−27.1
1/6	TAN13	−18.2	−20.8	NA		−21.5	−18.2	−23.3
2/6	TAN14	−18.1	−21.8	−19.8		NA	−25.3	NA
4/6	TAN15	−19.8	−18.8	−24.8		−22.7	−29.7	−23.9
5/6	TAN16	−17.3	−18.6	−21.3		NA	−33.0	NA
6/6	TAN17	−15.7	−18.5	−23.6		NA	−27	−30.6
7/6	TAN18	−24.5	−19.5	−21.2		NA	−35.4	−27.8
9/6	TAN19	−23.1	−21.7	−23.9		NA	−22.8	−18.8
12/6	TAN20	−20.1	−19.2	−22.6		NA	−31.1	NA
28/7	TAN21	−19.5	−19.0	−21.4	−29.8	−24.2	−23.5	−17.9
29/7	TAN22	−16.2	−18.5	−26.1	NA	NA	−18.8	NA
1/8	TAN23	−17.3	−17.4	−20.2	−26.7	−25.4	−24.5	−20.2
2/8	TAN24	−17.6	−20.5	−23.4	−26.3	NA	−21.6	−21.1
3/8	TAN25	−26.4	−29.0	−32.2	−33.4	−30.5	−31.6	−29.0
4/8	TAN26	−18.8	−19.3	−21.4	−26.3	−25.3	−24.4	−15.8
5/8	TAN27	−21.5	−20.9	−24.4	NA	NA	−26.9	−20.6
6/8	TAN28	−18.3	−18.9	−25.8	NA	NA	−26.3	−24.8
7/8	TAN29	−24.3	−18.8	−23.5	NA	NA	−36.5	NA
8/8	TAN30	−16.2	−17.1	−18.5	NA	−26.7	−21.3	NA
	Mean	−19.9±	−20.2	−23.3	−28.5	−25.2	−26.7	−23.7
	±SD	3.1	2.7	3.2	3.1	2.9	5.1	4.8

Analytical errors for δ¹³C are within 0.2‰.

NA: Not available.

Fig. 3 Box plot of stable carbon isotope ratios of diacids, glyoxylic acid (ωC₂) and glyoxal (Gly) in PM_2.5 and PM₁₀ aerosols from Morogoro, Tanzania, collected during the campaign. Each box shows the median (black line), the interquartile range (box) and the minimum and maximum values. Open circles show the outliers.

Fig. 4 Relation between concentrations of oxalic (C₂) acid and its relative abundance to total diacids in PM_2.5 and PM₁₀ during 2011 sampling period in Morogoro, Tanzania. Data from Mkoma and Kawamura (2013).

Fig. 5 Plot showing the linear relation of stable carbon isotopic composition (δ¹³C) for (a) C₂, (b) C₃, (c) C₄ and (d) ωC₂ acids with relative abundance of oxalic acid (C₂%) to total diacids in PM_2.5 during 2011 sampling campaign in Morogoro, Tanzania.

Fig. 6 Relation between stable carbon isotope ratios (δ¹³C value) of diacids and WSOC/OC ratio in PM_2.5 during 2011 sampling period in Morogoro, Tanzania.