Polycyclic Aromatic Hydrocarbons in Urban Air: Concentration Levels, Patterns, and Source Analysis in Nairobi, Kenya

Figures & data

Figure 1 Sampling sites in the city of Nairobi, Kenya.

Table 1 Sampling information in Nairobi, Kenya

	Sampling period		Temperature °C		Humidity %		Volume
Sampling area	Time	Date	max	min	at 3 pm	at 9 am	L
Traffic	11.30–14.30	25-Aug-03	25	12	49	77	865
Traffic	15.30–19.30	03-Sep-03	23	13	54	85	902
Traffic	13.30–16.30	04-Sep-03	26	11	36	72	879
Traffic	10.00–13.00	06-Sep-03	27	11	39	98	914
Traffic	09.00–12.00	09-Sep-03	23	13	52	71	931
Traffic	09.00–12.00	02-Sep-03	21	13	52	80	463
Traffic	09.00–12.00	05-Sep-03	27	14	36	84	902
Traffic	09.30–12.30	10-Sep-03	29	14	45	80	911
Traffic	10.00–13.00	11-Sep-03	25	12	45	72	892
Traffic	09.00–12.00	12-Sep-03	25	12	57	72	901
Industrial	14.00–17.00	02-Sep-03	21	13	52	80	454
Industrial	10.00–13.00	03-Sep-03	23	13	54	85	902
Industrial	09.00–12.00	04-Sep-03	26	11	36	72	914
Industrial	14.00–17.00	05-Sep-03	27	14	36	84	865
Industrial	12.00–15.00	09-Sep-03	23	13	50	71	889
Industrial	14.00–17.00	10-Sep-03	29	14	45	80	901
Industrial	14.00–17.00	11-Sep-03	25	12	45	72	877
Industrial	13.00–16.00	12-Sep-03	25	12	57	72	470
Residential	19.00–21.30	02-Sep-03	21	13	52	80	767
Residential	19.30–22.00	03-Sep-03	23	13	54	85	762
Residential	19.00–21.00	04-Sep-03	26	11	36	72	492
Residential	17.00–20.00	08-Sep-03	24	13	52	87	853
Residential	17.00–20.00	09-Sep-03	23	13	50	71	895
Residential	19.30–21.00	10-Sep-03	29	14	45	80	707

Table 2 Ranges and median concentrations of 25 PAHs (ng·m ⁻³) in Nairobi, Kenya

	Traffic area (n = 10)		Industrial area (n = 8)		Residential area (n = 6)
PAHs (abbreviation)	Range	Median	Range	Median	Range	Median
Fluorene (Flu)	0.6–16.4	2.1	0.8–9.7	1.8	0.6–7.3	2.5
Dibenzothiophene (Dbt)	0.6–6.6	3.8	2.1–7.9	3.3	2.8–7.8	4.1
Phenanthrene (Phe)	3.2–24.8	9.0	5.3–16.2	7.8	6.1–13.3	7.8
Anthracene (Ant)	0.5–8.1	2.4	1.2–3.3	1.7	1.4–8.7	5.0
3,6-Dimethyl phenanthrene (3,6-dm Phe)	0.5–7.7	3.0	1.0–2.9	1.6	1.0–4.7	1.8
Fluoranthene (Fth)	2.2–18.6	12.3	3.6–14.1	7.6	3.8–16.5	11.9
Pyrene (Py)	2.7–34.0	22.7	5.5–23.2	11.5	5.0–26.6	17.8
Retene (Ret)	0.8–13.3	4.5	1.6–5.7	2.7	1.9–11.0	4.4
Benzo[c]phenanthrene (B[c]P)	0.4–11.0	2.1	0.8–2.8	1.7	1.0–4.0	3.2
Benzo[a]anthracene (B[a]A)	1.0–17.3	10.4	3.1–12.6	6.2	4.9–22.5	10.8
Chrysene (Chy)	1.0–19.0	12.5	3.8–13.7	7.8	4.8–19.0	10.7
Benzo[b]fluoranthene (B[b]Fth)	0.8–35.8	8.1	3.8–31.0	6.4	5.3–9.1	8.1
7,12-dimethyl benz[a]anthracene (7,12-dmB[a]A)	0.1–2.9	0.3	0.2–4.0	0.3	0.3–11.5	0.5
Benzo[j+k]fluoranthene (B[j+k]Fth)	0.6–13.5	4.3	1.8–4.5	3.1	3.4–10.8	4.8
Benzo[e]pyrene (B[e]P)	1.1–21.0	12.4	4.7–11.0	7.1	5.2–11.9	7.3
Benzo[a]pyrene (B[a]P)	0.9–16.1	10.1	2.7–10.8	5.0	4.6–16.1	8.1
3-Methyl cholanthrene (3-Me Chol)	0.1–8.1	0.4	0.4–4.6	0.6	0.1–3.5	0.4
Indeno[1,2,3-cd]pyrene (IP)	1.4–17.0	12.7	4.1–12.9	8.0	6.0–11.0	7.4
Dibenzo[a,h]anthracene (Db[a,h]A)	0.3–9.9	0.8	0.2–1.8	0.6	0.5–2.9	1.4
Benzo[ghi]perylene (B[ghi]P)	1.9–43.1	31.3	9.0–24.6	15.8	7.4–13.8	7.6
Dibenzo[a,l]pyrene (Db[a,l]P)	0.4–10.0	1.6	0.7–3.8	1.2	1.0–3.3	1.8
Dibenzo[a,e]pyrene (Db[a,e]P)	0.3–18.8	2.4	1.1–3.3	1.7	0.8–2.4	1.4
Coronene (Cor)	1.2–29.2	19.1	5.2–14.7	8.9	2.8–8.1	5.1
Dibenzo[a,i]pyrene (Db[a,i]P)	0.2–4.3	0.4	0.2–0.6	0.4	0.0–2.1	0.6
Dibenzo[a,h]pyrene (Db[a,h]P)	0.2–4.5	0.4	0.1–1.5	0.5	0.3–2.1	0.6
Total	23.5–328.9	200.9	66.9–185.9	128.2	86.0–201.7	140.9

Figure 2 GC/MS chromatogram showing some of the PAHs detected in a traffic sample.

Figure 3 Average percentage contribution of the 25 PAHs from sampling areas.

Table 3a Summary of isomer ratios of selected PAHs

	Traffic area		Industrial area		Residential area
Isomer ratios	Range	Average	Range	Average	Range	Average
Fth/(Fth + Py)	0.26–0.46	0.37	0.32–0.45	0.39	0.08–0.42	0.41
B[a]A/Chy	0.76–1.13	0.91	0.61–1.50	0.87	0.77–1.25	1.06
B[a]A/(B[a]A +Chy)	0.43–0.53	0.48	0.38–0.60	0.46	0.43–0.56	0.51
B[e]P/(B[e]P+B[a]P)	0.49–0.69	0.56	0.45–0.69	0.58	0.36–0.63	0.48
B[ghi]P/B[a]P	1.65–4.12	2.81	2.28–3.42	2.89	0.47–3.04	1.39
B[ghi]P/B[e]P	1.16–3.34	2.20	1.27–2.79	2.09	0.63–1.81	1.32
IP/(IP+B[e]P)	0.42–0.56	0.51	0.44–0.60	0.51	0.41–0.59	0.51
Cor/B[e]P	0.46–2.09	1.35	0.82–1.67	1.20	0.32–1.07	0.75
IP/(IP+B[ghi]P)	0.27–0.46	0.33	0.29–0.46	0.34	0.31–0.53	0.45

Table 3b Reference isomer ratios of selected PAHs from previous research

	Traffic sources		Combustion
Isomer ratios	Diesel	Gasoline	Oil	Wood	Others industrial
Fth/(Fth + Py)	0.38 ^a , 0.60–0.70 ^d	0.17 ^a , 0.40 ^b	0.62 ^a
	0.41 ± 0.10 ^k
B[a]A/Chy	0.53 ± 0.06 ^f			0.79 ± 0.13 ^f	0.60 ± 0.06 ^f
B[a]A/(B[a]A +Chy)	0.38–0.64 ^d	0.43 ^b	0.32 ^a	0.50 ^b
B[e]P/(B[e]P+B[a]P)	0.64 ^a , 0.70 ^b	0.87 ^a	0.68 ^a	0.34 ^g
	0.45 ± 0.27 ^k
B[ghi]P/B[a]P	1.16 ^a , 1.2–2.2^b	1.72 ^a , 2.5–3.3 ^b	0.40 ^a		1.69–8.63 ^a
Cor/B[e]P	1.8 ^i , 1.54 ± 0.16 ^j				0.35–0.48 ^h
IP/(IP+B[ghi]P)	0.32 ± 0.22 ^k
	0.35–0.70 ^b	0.21–0.22 ^c	0.82 ^a	> 0.5 ^e
, , , , , , , , , ,

Figure 4 Plot of isomer ratios B[a]A/(B[a]A + Chy) versus IP/(IP + B[ghi]P).

Table 4 Correlations of selected PAHs in the sampling areas

PAH	TA	IA	RA
B[ghi]P - Cor	R = 0.97 n = 10	R = 0.97, n = 8	R = 0.91, n = 6
Py - Fth	R = 0.62, n = 10	R = 0.93, n = 8	R = 0.93, n = 6
Py - B[a]A	R = 0.32, n = 10	R = 0.98, n = 8	R = 0.58, n = 6
Py - B[a]P	R = 0.23, n = 10	R = 0.93, n = 8	R = 0.33, n = 6
Fth - B[a]P	R = − 0.16, n = 10	R = 0.92, n = 8	R = 0.45, n = 6
Chy - B[a]A	R = 0.76, n = 10	R = 0.52, n = 8	R = 0.93, n = 6
Chy - Fth	R = − 0.04, n = 10	R = 0.65, n = 8	R = 0.90, n = 6
IA = industrial area, n = number of samples, R = correlation coefficient, RA = residential area, TA = trafficked area

Figure 5a PCA scores of the individual PAHs normalized by total percentage.

Figure 5b PCA loadings of the individual PAHs normalized by total percentage.

Table 5 PCA loadings for particle bound PAHs in Nairobi

PAHs	Factor 1	Factor 2	Factor 3	Factor 4
Fth	0.73	−0.09	0.25	0.06
Py	0.69	−0.64	0.21	0.04
Ret	0.10	0.53	0.62	0.36
B[a]A	0.87	0.10	−0.39	0.00
Chy	0.76	0.12	−0.36	−0.24
B[b]Fth	−0.58	0.65	0.21	−0.24
B[j+k]Fth	−0.01	0.91	−0.26	−0.05
B[e]P	−0.64	0.23	−0.28	−0.56
B[a]P	0.68	0.02	−0.60	0.20
IP	−0.48	−0.27	−0.12	0.45
Db[a,h]A	−0.14	0.73	−0.23	0.48
B[ghi]P	−0.57	−0.78	−0.17	0.01
Db[a,e]P	−0.57	0.20	−0.40	0.32
Cor	−0.64	−0.68	−0.25	0.13
Variance attributed to each factor
	4.9	3.8	1.6	1.2
Percentage	35.0	27.0	12.0	8.0

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