Fig. 1. Schematic diagram of the experimental setup of the MAX-DOAS instrument

Fig. 2. The measurement routes taken and Hengshui city structure during this campaign

Fig. 3. NO₂ fitting case of a measurement spectrum

Fig. 4. NO₂ time series (a) and correlation (b) between the stationary and mobile MAX-DOAS during the inter-comparison measurement

Fig. 5. Spatial distribution of NO₂ VCDs and the wind information during this campaign
The black arrow represents the wind field information, and the red five-pointed star represents the location of the stationary MA-DOAS

Fig. 6. Comparison of NO₂ between the stationary and mobile MAX-DOAS during the mobile measurement on February 9, 2018
Yellow shadow: the time when the vehicle approaching the stationary MAX-DOAS;Gray shadow: time when the vehicle reached the eastern region of Hengshui

Fig. 7. Spatial distribution of tropospheric mean NO₂ VCDs measured by OMI satellite from 16th Jan 2018 to 15th Feb 2018. The 0~100 m 24 h backward trajectories of air masses are also shown to illustrate the transportation of atmospheric NO₂ during the measurement campaign
The green, brown and pink lines indicate the clusters in different directions

Table 1. Driving direction, wind field and weather conditions during this campaign

Table 2. Parameter settings used for NO₂ DSCD retrieval

Table 3. NO₂ Mean VCDs of each area of Hengshui during the mobile MAX-DOAS measurement (10¹⁵ molecule·cm^-2)

Table 4. NO₂ emissions, input and output flux from outer route of Hengshui (10²⁴ molecs^-1)