Spatial analysis of NO₂ and SO₂ exposure in relation to residential areas and healthcare accessibility in Sri Lanka using Sentinel-5P and GIS

Air pollution represents a growing environmental and public health challenge globally, with nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) among the most damaging pollutants to human respiratory and cardiovascular health. In Sri Lanka, rapid urbanization and industrial expansion have intensified exposure, particularly in the Western Province and industrial zones such as Puttalam and Kalutara, while the limited ground-based monitoring network constrains national spatial assessment. This study integrates Sentinel-5P TROPOMI satellite data with residential and healthcare facility location data through GIS-based spatial analysis to assess NO₂ and SO₂ exposure risks and spatial disparities in healthcare access across Sri Lanka. Tropospheric column densities from Near-Real-Time (NRTI) and Offline (OFFL) products for December 2024 were extracted via Google Earth Engine and converted to parts per billion (ppb) using an altitude-corrected conversion, then overlaid with residential town and hospital locations from the Humanitarian Data Exchange (HDX). Six districts, Colombo, Gampaha, Kalutara, Galle, Kegalle, and Ratnapura, recorded mean OFFL NO₂ exceeding 1.0 ppb, collectively containing 133 residential town points representing approximately 9.8 million people. SO₂ concentrations were highest in Kegalle (4.25 ppb), Kalutara (4.08 ppb), and Colombo (4.00 ppb). Healthcare facility coverage, screened as the ratio of hospital to residential town points, was markedly lower in Batticaloa (0.40), Puttalam (0.58), and Monaragala (0.55) than in Colombo (2.22), independent of each district’s absolute SO₂ level. The OFFL dataset provided spatially consistent estimates suitable for long-term planning, whilst NRTI captured finer spatial variation. These results demonstrate the utility of combining satellite air quality data with GIS infrastructure layers as a cost-effective screening tool for identifying exposure risk and healthcare preparedness gaps, with direct relevance to environmental planning and public health policy in Sri Lanka.