Table 1. Mean OC/EC ratios in PM_2.5 of tunnel studies.

Tunnel	City	Mean OC/EC	Analytical method	Reference
Zhujiang tunnel	Guangzhou	0.49	Thermal optical transmittance	He et al. [9]
Tanglang Hill tunnel	Shenzhen	0.52	Thermal optical transmittance	Liu et al. [23]
Xueshan Tunnel	Taiwan	1.26	Thermal optical reflectance	Zhu et al. [25]
Mount Victoria tunnel	Wellington	1.00	Thermal optical reflectance	Ancelet et al. [17]
Janio Quadios tunnel	Sao Paulo	1.59	Thermal optical transmittance	Brito et al. [18]
Rodoanal Mario Covas tunnel	Sao Paulo	0.49	Thermal optical transmittance	Brito et al. [18]
Sepulveda tunnel	Los Angeles	0.76	Thermal optical reflectance	Gillies et al. [20]
Squirrel Hill tunnel	Pittsburgh	1.00	Thermal optical transmittance	Grieshop et al. [21]
Urban tunnel	Marseille	0.56	Thermal optical transmittance	Haddad et al. [19]
Kaisermühlen tunnel	Vienna	0.30	Thermal two step combustion	Handler et al. [22]
Marquês de Pombal tunnel	Lisbon	0.29∼0.37	Thermal optical transmittance	Pio et al. [24]
Xiangyin tunnel	Shanghai	1.34	Thermal optical reflectance	this study