Fig.1

Distribution and elevation of national meteorological observation stations and environmental monitor stations in the Beijing-Tianjin-Hebei region"

Fig.2

Variations of radiation fog days (a), minimum visibility during radiation fog (b), and visibility at 08:00 (c) in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.3

Monthly variations of radiation fog days in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Table 1

High-low temperature differences on radiation fog days in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.4

Box chart of frequency variations in high-low temperature differences on radiation fog days in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.5

The relationship between the high-low temperature differences on radiation fog days and relative humidity at 14:00 on the day before radiation fog days in the whole year (a), winter (b) and summer (c) in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Table 2

Wind speed variations before and after radiation fog in the Beijing-Tianjin-Hebei region from 2002 to 2020  m·s-1"

Fig.6

Box plots of wind speed frequency variations before and after radiation fog in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.7

Surface wind rose plots at 14:00 (a) and 20:00 (b) on the previous day and at 08:00 on the radiation fog day (c) in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.8

Vertical profile of relative humidity on radiation fog days in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.9

Wind speed at various heights on radiation fog days in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.10

Wind rose plots at the height of 1000 hPa (a), 850 hPa (b), 700 hPa (c), 500 hPa (d) on radiation fog days in the Beijing-Tianjin-Hebei region from 2002 to 2020"

Fig.11

Three types of inversion layer with grounded the bottom of the inversion layer (a), the deep inversion layer deep (b) and not grounded the bottom of the inversion layer (c) on radiation fog days"

Fig.12

Variations of height (a) and thickness (b) of inversion layer on radiation fog days"

Table 3

Comparisons of air quality and major pollutant concentrations on and one day before radiation fog days in Hebei province from 2013 to 2018"