6.2. Pollution some toxic gases of CO, SO2, NO2 in the air in urban areas generally within the allowable limits. However, in some places, and in some time, the concentration of this substance has increased, some cases have exceeded the permitted value. Due to the impact of transport activities, NO2 levels near the road traffic is much higher than other areas. Especially in the densely urban transport such as TP. Ho Chi Minh, the concentration of NO2 in the air is much higher than other urban areas (Figure 12). This proves that NO2 is generated primarily from activities in the city traffic.
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