Driver exposure to particulate matter in Bangkok

Figures & data

Table 1. Exposure levels to PM_2.5 * (μg/m³) of four driver types and outside the taxi (a) and four routes (b) in August 2008 and January 2009

	August 2008				January 2009
	Mean	Median	Range	n	Mean	Median	Range	n
(a)
Air-con bus	36	32	23–68	7	84	90	54–113	8
Non-air-con bus	63	58	39–105	7	125	123	104–143	8
Tuk-tuk	86	80	50–131	9	198	179	150–336	8
Taxi (inside)	52	52	34–97	10	110	110	78–155	8
Taxi (outside)	63	55	48–116	8	134	127	99–196	8
(b)
Route No. 4	64	51	31–131	11	108	104	59–201	8
Route No. 12	58	58	23–84	6	153	132	93–336	8
Route No. 29	64	70	32–104	7	129	123	54–222	8
Route No. 93	54	52	27–99	9	127	120	89–195	8
Notes: *PM2.5 levels in January were significantly higher than those in August on each of the driving routes by Mann-Whitney U test; (a) P< 0.01, (b) P < 0.05.

Table 2. Exposure levels to PM_10–2.5 * (μg/m³) of four driver types and outside the taxi (a) and four routes (b) in August 2008 and January 2009

	August 2008				January 2009
	Mean	Median	Range ^#	n	Mean	Median	Range	n
(a)
Air-con bus	6.9	0.05	0.05–23	7	26.3	26	5–50	8
Non-air-con bus	29.4	21	16–60	7	56.7	61	19–73	8
Tuk-tuk	25.1	23	0.05–60	9	46.9	47	23–68	8
Taxi (inside)	2.5	0.05	0.05–15	10	12.6	12	6–20	8
Taxi (outside)	22.1	18	6–50	8	44.5	43	20–77	8
(b)
Route No. 4	21.9	18	0.05–60	11	18.4	15	5–40	8
Route No. 12	7.2	3	0.05–21	6	40.8	40	14–73	8
Route No. 29	9.7	14	0.05–24	7	37.9	35	8–63	8
Route No. 93	16.0	10	0.05–47	9	43.8	47	10–72	8
Notes: *PM10–2.5 levels in January were significantly higher than those in August driving on routes Nos. 12, 29, or 93 by Mann-Whitney U test; (a) P < 0.01, (b) P < 0.01.
^#PM10–2.5 levels below the detection limit were set at 0.05.

Table 3. The proportions of PM_2.5 levels to PM₁₀ levels of four driver types and outside the taxi (a) and on four routes (b) in August 2008 and January 2009

	August 2008				January 2009
	Mean	Median	Range ^#	n	Mean	Median	Range	n
(a)
Air-con bus	0.75	0.75	0.73–0.75	3	0.78	0.77	0.65–0.92	8
Non-air-con bus	0.70	0.73	0.52–0.81	7	0.70	0.67	0.65–0.85	8
Tuk-tuk	0.76	0.76	0.60–0.88	8	0.81	0.79	0.76–0.87	8
Taxi (inside)	0.91	0.91	0.87–0.94	3	0.90	0.90	0.85–0.93	8
Taxi (outside)	0.76	0.77	0.65–0.92	5	0.76	0.77	0.64–0.89	8
(b)
Route No. 4	0.72	0.72	0.60–0.87	8	0.86	0.86	0.72–0.93	8
Route No. 12	0.82	0.82	0.74–0.91	3	0.79	0.80	0.66–0.90	8
Route No. 29	0.82	0.73	0.75–0.88	7	0.77	0.77	0.65–0.93	8
Route No. 93	0.73	0.73	0.52–0.94	6	0.75	0.76	0.65–0.90	8
Note: ^#PM10–2.5 levels below the detection limit were excluded.

Table 4. Total carbon (TC) exposure levels in the PM_2.5 and three relevant proportions (TC levels to PM_2.5 levels, organic carbon [OC] levles to PM_2.5 levels, and OC levels to TC levels [mean ± SD]) in August 2008 (a) and January 2009 (b)

	n	TC*	TC/PM2.5	OC/PM2.5	OC/TC*
(a) August 2008
Air-con bus	7	31 ± 7	0.95 ± 0.33	0.46 ± 0.16	0.50 ± 0.7
Non-air-con bus	7	57 ± 26	0.89 ± 0.20	0.42 ± 0.11	0.48 ± 0.04
Tuk-tuk	9	75 ± 14	0.93 ± 0.27	0.54 ± 0.17	0.59 ± 0.06
Taxi (inside)	10	52 ± 10	1.07 ± 0.31 ^#	0.50 ± 0.19	0.46 ± 0.08
Total	33	55 ± 22	0.97 ± 0.28	0.49 ± 0.16	0.51 ± 0.08
(b) January 2009
Air-con bus	8	54 ± 8	0.67 ± 0.13	0.44 ± 0.10	0.65 ± 0.04
Non-air-con bus	8	71 ± 14	0.57 ± 0.12	0.34 ± 0.08	0.60 ± 0.07
Tuk-tuk	8	123 ± 22	0.65 ± 0.15	0.47 ± 0.13	0.72 ± 0.06
Taxi (inside)	8	77 ± 18	0.71 ± 0.08	0.43 ± 0.07	0.62 ± 0.05
Total	32	81 ± 30	0.65 ± 0.13	0.42 ± 0.11	0.65 ± 0.07
Notes: *All of the exposure levles to TC and OC/TC differed significantly among the four driver types by Kruskal-Wallis rank-sum test (P < 0.01).
^# The reason for TC > PM2.5 is described in the Discussion.

Table 5. Exposure levels (mean ± SD) to total carbon (TC), organic carbon (OC), and elemental carbon (EC) in the PM_2.5 of the drivers on the four driving routes in Bangkok in August 2008 (a) and January 2009 (b)

	n	TC	OC	EC	P Value*
(a) August 2008
Route No. 4	12	58 ± 24	33 ± 14	25 ± 10	0.003
Route No. 12	7	56 ± 21	26 ± 14	29 ± 10	0.499
Route No. 29	8	64 ± 19	29 ± 11	35 ± 12	0.123
Route No. 93	10	48 ± 19	24 ± 14	24 ± 7	0.386
Total	37	56 ± 21	29 ± 13	28 ± 10	0.690
(b) January 2009
Route No. 4	8	82 ± 40	56 ± 33	26 ± 8	0.012
Route No. 12	8	91 ± 32	56 ± 25	36 ± 11	0.012
Route No. 29	8	79 ± 23	44 ± 15	35 ± 11	0.017
Route No. 93	8	73 ± 27	44 ± 21	29 ± 7	0.012
Total	32	81 ± 30	50 ± 24	31 ± 10	<0.001
Notes: *Difference between OC and EC levels by Mann-Whitney U test.

Figure 1. Bangkok bus routes and Pollution Control Department stations. PCD = Pollution Control Department, Ministry of Natural Resources and Environment.