<p>This study represents the extensive investigation of particulate matter (PM) concentrations in indoor environments in India, analyzing PM₁₀, PM_2.5, and PM₁ levels across 109 locations in the Mumbai Metropolitan Region (MMR), India. The monitored locations included residences, offices, restaurants, shopping malls, and cinema theatres, providing comprehensive insights into spatial and temporal variations. Results indicate that indoor PM levels frequently exceed WHO and NAAQS guidelines, with the highest concentrations observed in restaurants and residences. Restaurants recorded the highest mean PM₁₀ (94.2 ± 45.1&#xa0;µg m^-3) and PM_2.5 (38.3 ± 25.7&#xa0;µg m^-3) primarily due to cooking emissions and inadequate ventilation. Residences followed, with mean PM₁₀ and PM_2.5 levels of 83.6 ± 39.3&#xa0;µg m^-3 and 30.7 ± 17.8&#xa0;µg m^-3, respectively. Homes near industrial zones had significantly elevated PM₁₀ levels (116.2 ± 59.0&#xa0;µg m^-3) highlighting the impact of external pollution infiltration. In contrast, private offices and shopping malls with well-maintained HVAC systems exhibited lower PM10 concentrations (65.8 ± 40.0&#xa0;µg m^-3 and 72.1 ± 31.2&#xa0;µg m^-3, respectively). Temporal analysis revealed that peak-hour PM₁₀ concentrations in cinema halls (105.1 ± 52.9&#xa0;µg m^-3) were nearly 1.7 times higher than during non-peak hours (63.8 ± 23.1&#xa0;µg m^-3), largely due to foot traffic and dust resuspension. The findings underscore the urgent need for IAQ regulations, enhanced ventilation strategies, and stricter emission controls to mitigate health risks. This research provides crucial data for policymakers and urban planners, facilitating evidence-based interventions to improve indoor air quality and safeguard public health.</p>