Rapid urban growth and industrial activity have significantly increased air pollution in Chattogram, Bangladesh. Among various pollutants, particulate matter (PM_2.5 and PM₁₀) has emerged as a major concern due to its severe effects on public health and the environment. This study investigates seasonal and temporal variations in air quality and identifies periods of high risk. Data were collected from the Department of Environment, including PM_2.5 and PM₁₀ measurements from 2013 to April 2025 and AQI data from 2022 to April 2025. The analysis focuses on seasonal trends, monthly fluctuations, extreme pollution events, and correlations among pollutants. The study examines which seasons are most polluted and how PM_2.5, PM₁₀, and AQI change over the year. Results indicate that winter experiences the highest pollution levels, while monsoon shows the lowest. Pre-monsoon and post-monsoon show moderate pollution, representing transitional periods with variable air quality. Monthly trends reveal that pollution peaks in January and reaches its lowest point in July, demonstrating clear temporal patterns. Extreme pollution events are most frequent in winter and the pre-monsoon period, emphasizing periods of highest health risk. Correlation analysis shows strong positive associations between PM_2.5, PM₁₀, and AQI (r > 0.80). Machine-learning models demonstrated moderate predictive skill for PM₁₀ forecasting (R² up to 0.65), while PM_2.5 models at Agrabad produced negative R² values, indicating performance worse than a mean-value benchmark; accordingly, long-term PM_2.5 projections at Agrabad are not reported. Exploratory PM₁₀ projections suggest that concentrations may remain above WHO guideline levels through 2030, although these projections should be interpreted cautiously because meteorological drivers were not included in the modelling framework. The findings highlight the need for seasonal interventions to control particulate matter, particularly in winter and pre-monsoon. Measures such as stricter emission regulations, industrial controls, and public awareness campaigns are essential for mitigating health risks. This study provides a comprehensive understanding of air-quality dynamics in Chattogram and offers a framework for targeted pollution-control strategies. Implementing these strategies can improve air quality, protect public health, and support sustainable urban development.

Anthropogenic air pollution represents a significant threat to both environmental and human health, with nitrogen oxides (NO_x) playing a substantial role in the formation of photochemical smog, acid rain, eutrophication, and respiratory diseases. In Bangladesh, NO_x emissions primarily originate from combustion sources such as road transportation, power generation, and industrial activities, while natural sources include lightning, wildfires, and soil emissions. Furthermore, ammonia emissions from fertilizers and livestock exacerbate air quality issues in both urban and rural settings. Despite the acknowledgment of vehicular and industrial contributions, comprehensive and systematic assessments of NO₂ trends across the nation remain scarce. This study presents a complementary, side-by-side assessment of ground-based NO₂ measurements from the Department of Environment (DoE) with atmospheric NO₂ retrieved from the Sentinel-5P TROPOMI Level-3 product via Google Earth Engine (GEE). Spatial distribution patterns of both ground-level and atmospheric NO₂ were analyzed using ArcGIS Pro, along with seasonal and interannual trend assessments from 2018 to 2024. Results indicated pronounced spatial and temporal variability in NO₂ concentrations. The highest levels were consistently recorded over Dhaka and surrounding industrial zones, with moderate accumulation in Chattogram. Winter months (December–February) exhibited hazardous concentrations, with a national maximum of 205.21 µg/m³, while monsoon periods recorded the lowest levels overall, as reflected in its seasonal mean (see below). Seasonal averages indicated the highest concentrations in winter (35.03 µg/m³), followed by pre-monsoon (29.16 µg/m³), with monsoon recording the lowest seasonal mean (19.94 µg/m³). Long-term analysis showed the highest national annual mean NO₂ con-centration in 2018 (44.32 µg/m³), decreasing to 14.81 µg/m³ by 2024, with non-monotonic year-to-year fluctuation in the intervening period (2020–2021 data were unavailable). These findings underscore the necessity for stricter emission regulations and targeted mitigation measures. As a policy recommendation, this may include the implementation of NO_x-selective catalytic reduction (SCR) using NH₃ over metal oxide and zeolite catalysts. This study provides evidence-based insights to support cleaner air initiatives and sustainable environmental management strategies in Bangladesh.