Assessment of Seasonal Air Quality Variations in Biratnagar, Nepal: A Comprehensive Multi-Month Comparative Analysis with Regional Implications

The study involved air quality monitoring of Biratnagar, a big industrial city in Southeastern Nepal, in four seasons in 2021. The analysis based on the measurement of the various forms of particulate matter (PM1, PM 2.5, PM 10 and TSP) indicates a cataclysmic change in season. The most polluted period is during winter, the average of 155.2 AQI is (Unhealthy), but it is dramatically lower than the average in April of 102.6 before the monsoon. The monsoon is a much needed clean up, purifying the air by an average of 80 percent to a level of Good AQI of 20.3 in June. Although the highest pollution often occurs on days (around 175) at night in winter with temperature inversions and dead air, there is always a safe window in the day. The air quality is much better between 10:00 AM and 5:00 PM with the cleanest air quality recorded at 2:00 PM when solar heating enables the atmosphere to blow out the pollutants. The paper contrasts the patterns with other cities in South Asia to spot the special status of Biratnagar in the Indo-Gangetic Plain and recommends a multi-cyclic model of management, integrating the regional control of its emissions and special safety measures of high-risk winter evenings to be adopted.