Table 4.

Association between PM_2.5 levels and daily traffic load of different type of vehicles at traffic station in Chiayi County through the generalized estimating equation approach

Car type	Mean (SD)	Min–Max
Motorcycle (10,000/day)	0.25 (0.32)	0–1.53
Sedan (10,000/day)	0.92 (0.71)	0.05–2.84
Bus (1000/day)	0.16 (0.13)	0–0.7
Truck (1000/day)	0.54 (0.52)	0.01–1.93

	Unstructured structure				Exchangeable structure				Autoregressive structure
Car type	β	SE	p-value	QIC	β	SE	p-value	QIC	β	SE	p-value	QIC
Motorcycle	− 0.66	0.55	0.23	1880.28	0.65	0.61	0.29	1930.55	1.40	0.58	0.02	1920.68
Sedan	1.00	0.19	< 0.01	190.85	− 0.10	0.33	0.76	194.36	0.26	0.34	0.44	194.13
Bus	5.48	1.75	< 0.01	190.92	− 0.64	1.44	0.66	193.61	1.97	1.25	0.16	192.38
Truck	0.98	0.18	< 0.01	190.50	− 0.46	0.54	0.39	195.78	− 0.57	0.43	0.18	193.60