Role of Bay of Bengal cyclone in unusual aerosol loading and fog events over the Kerala regions

Atmospheric conditions show significant variations during cyclone advancement and landfall in tropical regions. Here, we investigate the unusual fog event over the Kerala region associated with the Mandous cyclone (December 6-10, 2022) in the Bay of Bengal (BoB). This study also investigates the variations in atmospheric aerosol loading and its potential source identification. Before the landfall of cyclone Mandous, there was a significant increase in aerosol concentration over the Kerala region. Changes in prevailing wind patterns due to BoB cyclones lead to long-range transport of aerosols from the Indo-Gangetic Plain (IGP) and Rajasthan region to the South Indian region. The changes in meteorological parameters during these days are analyzed. Previous studies reported increased aerosol concentration during cyclone formation, but such events still need to be reported in the Kerala region. Unusual fog events in the Kerala region are associated with this increased aerosol loading. From the HYSPLIT back trajectory analysis, it is evident that particulate matter (PM_2.5) has been brought to the Kerala region from multiple places in South Asia during these days. The IGP region contributes the majority of the transported aerosols. The average PM_2.5 mass concentration over the Kerala region shows a sharp increase during these days. Mandous form in winter (December), and the PBL height is low during this season. From analysis, it is clear that all meteorological parameters favor fog formation. The increased loading of atmospheric aerosol and moisture to the Kerala region during the study period was associated with the formation of the Mandous cyclone. Low ventilation coefficient values imply less vertical mixing and a stable atmosphere. So, these conditions lead to the observed abnormal fog events over the Kerala region. This kind of event is rare in South Indian regions but significantly impacts air quality and human health. Large-scale transport during cyclones increases the concentration of PM_2.5 in the south Indian region, leading to a poor Air Quality Index (AQI), significantly affecting human health.