## 1 Introduction  
An increasing trend in fog frequencies over South Asia has been observed during the winter season for the last few decades, which has resulted in large disruptions in the daily lives of people across the region [1]. Winter fog creates huge economic losses comparable to other extreme weather events such as hurricanes, storms, and tornadoes [2]. For instance, fog leads to poor visibility which hinders all means of transportation on a massive scale [1].  
Light wind, clear sky, high moisture and stable atmospheric conditions are more suitable for fog formation [3; 4]. Soil moisture is also considered as an important factor in remote sensing for fog monitoring [5]. In Pakistan, the Indus River and its tributaries along with soil moisture are considered as major sources air moisture and provide favourable conditions for fog formation. Additionally, large-scale dynamics play a vital role as El Nino conditions in the year 2004 influenced greater air pressure over Pakistan, increasing stability and resulting in favourable conditions for fog during winter months [1].  
Atmospheric aerosols are considered as a vital part of the energy balance system of Earth. As being one of the most important components of the atmosphere, they act as a seed for cloud/fog formation, resulting in precipitation. While an increase in their concentration in the atmosphere also causes negative effects on different natural processes: suppression of the precipitation rate of clouds, reduction of visibility and the cause of various health impacts [6; 7; 8; 9; 10]. Persistent fog happens over Pakistan during each winter, with high air pollution as a leading factor. Industrialization, urbanization, coal-based power generation, vehicular emissions and biomass burning are the main sources of air pollutants [11; 12; 13]. Fog also persists when large concentrations of aerosols are present, which characterize a low activation super saturation point [14]. When aerosol loads are elevated, they are considered to be an important factor contributing to persistent fog episodes. The increasing trend in fog occurrence over urban cities has been observed as mainly caused by a high pollution load resulting from multiple sources [15].  
Aerosols cause smog, air pollution [13; 16] and various impacts on cloud microphysics, global carbon, sulfur, nitrogen and hydrological cycles in both direct and indirect ways [17; 18; 19], and originate from sources with different properties [20]. Different types of aerosols have diverse properties on the symbol and extent of aerosol radiative forcing [21]. Black Carbon (BC) is considered as an absorbing aerosol that contributes to global warming [22; 23] and the extent of its impact varies in different parts of the world [22; 23]. Suspended dust particles alter the propagation of short and long wave radiation through atmospheric scattering and absorption methods [24] and warm the atmosphere due to absorption [25]. Aerosol also have impacts on social aspects like human health and ecological processes [26].  
Satellite remote sensing is an emerging field for global atmospheric monitoring of different parameters and their impact on climate, such as aerosols [27; 28]. Various studies have been conducted to explore aerosol trends [29; 30; 31; 32; 33; 34] and their effects at both the global and regional scales [35; 36] by utilizing satellite instruments. Additionally, AOD using AERONET data over the Lahore and Karachi stations has been successfully used to distinguish the origin of the aerosols [37; 38; 39; 40]. Low values of the Single Scattering Albedo (SSA) over Lahore (0.83- 0.91) compared to Karachi (0.88-0.97) were observed which indicates that absorbing aerosols are more dominant over Lahore station than Karachi [41].