This study investigates the increasing intensity and frequency of air pollution episodes in Lahore, Pakistan, referred to as "the fifth season" due to their recurrence during the post-monsoon and winter periods. The research utilizes ground-based and satellite observations to analyze time-series data on PM2.5 and AOD, meteorological and topographical data, and satellite data on UVAAI, CO, and fire counts. Key findings include: 1. **Increase in Air Pollution Sources**: There has been a significant increase in air pollution sources, particularly crop residue burning and motor vehicles, contributing to the frequency and intensity of pollution events. 2. **Meteorological and Topographical Factors**: The Indo-Gangetic Plain (IGP) provides ideal conditions for pollutant accumulation due to abundant cloud condensation nuclei and stable meteorological conditions, especially during post-monsoon and winter. 3. **Mann-Kendall Test**: The study confirms annual and seasonal trends in PM2.5 levels, showing a significant decline in major South Asian cities like Lahore, Delhi, Kathmandu, and Dhaka. 4. **Source Attribution**: An Analytical Hierarchy Process (AHP) was used to identify the most contributing factors to smog episodes, with transboundary pollution from open-field agriculture fires being the primary source, followed by vehicular emissions and thermal power generation. 5. **HYSPLIT Trajectory Model**: The model confirms the impact of transboundary emissions, particularly from agricultural fires in India, on air quality in Lahore, as evidenced by back trajectories and AOD data. The study highlights the need for regional cooperation and improved air quality monitoring infrastructure to address the transboundary nature of air pollution in the IGP.This study investigates the increasing intensity and frequency of air pollution episodes in Lahore, Pakistan, referred to as "the fifth season" due to their recurrence during the post-monsoon and winter periods. The research utilizes ground-based and satellite observations to analyze time-series data on PM2.5 and AOD, meteorological and topographical data, and satellite data on UVAAI, CO, and fire counts. Key findings include: 1. **Increase in Air Pollution Sources**: There has been a significant increase in air pollution sources, particularly crop residue burning and motor vehicles, contributing to the frequency and intensity of pollution events. 2. **Meteorological and Topographical Factors**: The Indo-Gangetic Plain (IGP) provides ideal conditions for pollutant accumulation due to abundant cloud condensation nuclei and stable meteorological conditions, especially during post-monsoon and winter. 3. **Mann-Kendall Test**: The study confirms annual and seasonal trends in PM2.5 levels, showing a significant decline in major South Asian cities like Lahore, Delhi, Kathmandu, and Dhaka. 4. **Source Attribution**: An Analytical Hierarchy Process (AHP) was used to identify the most contributing factors to smog episodes, with transboundary pollution from open-field agriculture fires being the primary source, followed by vehicular emissions and thermal power generation. 5. **HYSPLIT Trajectory Model**: The model confirms the impact of transboundary emissions, particularly from agricultural fires in India, on air quality in Lahore, as evidenced by back trajectories and AOD data. The study highlights the need for regional cooperation and improved air quality monitoring infrastructure to address the transboundary nature of air pollution in the IGP.