An extensive filter-based ambient aerosol measurement was carried out at a region that is mostly affected by fog almost every winter. A few fogwater samples were also collected during the study period. Water soluble organic matter (WSOM) was extracted in the aqueous media. The filter extracts and fogwater were analyzed for their chemical constituents using a High Resolution-Time of Flight-Aerosol Mass Spectrometer (HR-ToF-AMS). Data from the HR-ToF-AMS were used in positive matrix factorization (PMF) for the source apportionment to understand the sources of WSOM. Three major sources were identified, namely water soluble biomass burning organic aerosol (WS-BBOA), water soluble oxygenated organic aerosol (WS-OOA), and water soluble primary aerosol (WS-PA). The contributions of WS-BBOA and WS-OOA to WSOM were lower during foggy episodes than during clear (nonfoggy) episodes. The wet scavenging and removal of the aerosols from these sources were the prime causes of their lower contributions. The contribution of WS-PA to WSOM was higher during foggy episodes than during nonfoggy episodes. The higher contribution of this source is attributed to the accumulation of aerosol generated from this source, due to poor dispersion and the calm conditions prevalent during foggy episodes. Surprisingly, the contribution of WS-PA to WSOM was highest among the three sources during both foggy and nonfoggy episodes.