Synergistic Approach Towards the Implementation and Effectiveness of the Graded Response Action Plan (GRAP) on Air Quality in Delhi NCR

Urban ecosystems in megacities like Delhi are shaped by interactions between emissions, built structures, and seasonal meteorology, making policy evaluation vital for understanding environmental resilience and health risks. This study assesses the effectiveness of the Graded Response Action Plan (GRAP) which is Delhi’s tiered emergency framework that mandates escalating pollution-control measures during periods of severe air quality deterioration, across 2022-23, 2023-24, and 2024-25 by analysing high-resolution air quality variations at two contrasting urban settings; residential zone (Dwarka) and industrial cluster  zone (Mundka). Multi-pollutant datasets (PM₂.₅, PM₁₀, NO₂, SO₂, CO, and O₃) were examined across Pre-, During-, and Post-GRAP periods to capture seasonal dynamics and ecosystem-specific responses.

Across all years, particulate pollution showed sharp winter escalation, with PM₂.₅ rising from 40–90 µg/m³ in the Pre-GRAP window (defined as the 45 days prior to GRAP enforcement) to 130–230 µg/m³ during-GRAP, and PM₁₀ increasing from 150–300 µg/m³ to 300–400 µg/m³, with maxima exceeding 600–800 µg/m³ at specific sites. GRAP which typically is implemented for 6 to 8 months each year depending on prevailing pollution levels, which was then evaluated using this ±45-day framework to capture baseline and recovery phases. These particulate levels far exceed WHO and national limits, posing severe respiratory and cardiovascular risks. NO₂ often doubled during GRAP (reaching 50–70 µg/m³), while O₃ showed expected winter suppression (<20 µg/m³) and strong post-winter recovery (30–50 µg/m³), clearly reflected in the 45-day Post-GRAP period. Unlike other pollutants, SO₂ showed inconsistent GRAP influence, increasing during-GRAP and decreasing post-GRAP, indicating a significant policy gap especially in industrial zone where sulfur emissions persist. This is concerning because SO₂ forms sulfate aerosols, contributing to secondary PM and amplifying health impacts.

Although pollutants declined post-GRAP, they rarely returned to Pre-GRAP baselines, especially at industrial sites. Findings show that GRAP mitigates extreme peaks but remains insufficient, underscoring the need for ecosystem-specific, year-round emission controls particularly targeting sulfur sources to strengthen urban environmental health.