Vehicle Emission Factors for Particulate and Gaseous Pollutants in an Urban Tunnel in Xi’an, China

Table 2

Mean mass concentrations of pollutants at the outlet and inlet.

Pollutants	Inlet concentration (mg·m^−3)		Outlet concentration (mg·m^−3)
	Average	Standard deviation	Average	Standard deviation
PM2.5	0.048	0.023	0.054	0.023
CO	1.804	1.054	3.895	2.205
NOX	0.544	0.111	0.694	0.099
HC	3.615	0.277	5.129	0.289
VOCs	0.324	0.082	0.441	0.149