Human thermal load in the fog in the Hungarian lowland

Fog is one of the special weather phenomena of the Hungarian lowlands in autumn and winter. It has been studied from many points of view (for example frequency, type, predictability), but not yet from the point of view of human thermal load. The aim of this work is to fill this gap. We observed a total of 132 fog events at Martonvásár (Hungary, Central Transdanubian region) in the period 2017-2023. During our observations, we documented the period of its existence, air pressure, air temperature, air humidity and wind speed. Based on the meteorological and human (body mass, body length, sex, age, person walking at a speed of 1.1 m/s) data, we estimated the thermal load of the foggy environment using a clothing thermal resistance (r_cl)-operative temperature model. The model is very simple, based on the calculation of the energy balance of the human body covered with clothing. The main results are as follows. In the fogs that cause the greatest lack of heat, the r_cl is around 2.5 clo, the operative temperature is around -7 ℃.  In fogs with a much smaller heat deficit, the r_cl is around 0.5 clo, and the operative temperature is around 15-17 ℃. In the vast majority of cases, r_cl varies between 1-2 clo. We were able to make sure that the thermal load of the fog is mostly determined by the temperature and radiation conditions. Further observations are needed. For instance, one should observe the smallest thermal deficit, in which fog can still exist.