Spatio-Temporal Variability of Atmospheric and Ground Level NO2 in Bangladesh

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Abstract
Anthropogenic air pollution represents a significant threat to both environmental and human health, with nitrogen oxides (NOx) playing a substantial role in the formation of photochemical smog, acid rain, eutrophication, and respiratory diseases. In Bangladesh, NOx 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 NOx-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.

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