Investigation on the Time Factor of CO-Based Emission Factors for Sustainable Development of Urban Tunnels in China

Figure 4

The sampling points distribution in the four urban tunnels. (a) Henglong Mountain Tunnel. (b) Cejiexian Subway. (c) Jiuweiling Tunnel. (d) Dameisha Tunnel.

(a)

(b)

(c)

(d)