Beyond Single Pollutants: Quantifying Urban Population Exposure to Concurrent Air Pollution Hazards in big cities of Gujarat, India

Urban populations are frequently exposed to complex mixtures of air pollutants, a critical public health challenge as compound exposures often produce nonlinear, synergistic health impacts greater than the sum of individual risks. This study presents a high-resolution, satellite-based assessment of population exposure to concurrent exceedances of multiple air pollutants in Gujarat’s major metropolitan areas—Ahmedabad, Surat, Vadodara, and Rajkot—from 2019 to 2024.

We leverage advanced remote sensing data from the TROPOspheric Monitoring Instrument (TROPOMI) on Sentinel-5P and the Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua to monitor key pollutants, including Aerosol Optical Depth (AOD), Nitrogen Oxides (NOx), Sulfur Dioxide (SO2) and Methane (CH4) as a proxy for particulate matter. By analyzing spatiotemporal patterns, we identify and characterize episodic events where multiple pollutants simultaneously exceed baseline thresholds, creating potential ‘pollution cocktails’.

These multi-pollutant exceedance events are then integrated with high-resolution gridded population data to quantify the number and demographic distribution of residents exposed to compounded air quality risks. The methodology enables a shift from single-pollutant monitoring to a holistic exposure assessment framework.

Preliminary findings reveal significant temporal and spatial heterogeneity in compound exposure events, strongly influenced by urban form, industrial activity, and meteorological conditions. The analysis identifies recurring pollution hotspots and temporal patterns (e.g., seasonal, episodic) where populations face elevated health risks from concurrent pollutants. The results underscore that mitigation strategies focused on single pollutants may underestimate population health risks in these urban centers.

This study provides a critical evidence base for designing targeted, health-centric air quality management policies. By mapping compound exposure risks, it empowers urban planners and public health officials in Gujarat to prioritize interventions, optimize monitoring networks, and develop early warning systems that address the real-world, multi-pollutant environments experienced by urban populations, thereby strengthening resilience and advancing sustainable urban development goals.

Key Words: Compound Risk, Air Pollution, Satellite Data, Population Exposure