The meteorological surface variables and boundary-layer structures in the Seoul Metropolitan Area (SMA) were examined during the MAPS-Seoul (Megacity Air Pollution Studies in Seoul) intensive field experimental campaign (18 May to 13 June 2015). Data were obtained from a surface energy balance system and a ceilometer, installed at an UMS-Seoul (urban meteorological observation system network in SMA) Station located in the eastern part of Seoul City. A series of migratory anticyclone passages under a strong El-Niño event meant that the experimental period was much warmer and drier than the climatological ones. The period-mean air temperature was 2.6°C higher compared with recent 30-year (1981 to 2010) climatological one, while only one-eighth of the climatological precipitation was recorded. Twelve mist event days were recorded, as were four of haze, and six of rainfall events. The SMA was found to be affected by the sea-land breeze: westerly winds (sea-breeze) were dominant from the afternoon to the early evening, while easterlies (land-breeze) were dominant before morning. Finally, the vertical profile of attenuated backscatter obtained by a ceilometer indicated that the daily maximum mixing-layer heights (MLHs) on days with mist/haze and much cloud were lower than those on days with no-mist/haze and less cloud, respectively, mainly due to a decrease in the downward solar radiation. However, the effect of mist/haze on the daytime MLH evolution was larger than that of cloud cover. The MLH also showed a similar altitude with the steepest vertical gradient of sulfate and organic aerosol concentration obtained from the airborne measurement on 13 June 2015.