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

Figure 2

Diurnal variations in traffic volume and speed during the sampling period. Left axes show the number of vehicles during the morning transit (07:00–10:00), afternoon period (12:00–15:00), evening transit (17:00–20:00), and night period (22:00–24:00) from July 17 to July 27, 2015. The right axes show the corresponding average speed of the total fleets.