A Composite Environmental Quality Index: An Analysis of Air, Water (CEQI-AW) in Delhi from 2022 to 2025

Urban environmental degradation in India’s metropolitan centres poses escalating challenges for public health, economic productivity, and sustainable urban governance. Among these regions, the National Capital Region (NCR) especially Delhi continues to be one of the most environmentally stressed urban agglomerations, experiencing chronic air pollution, deteriorating water quality. Although several domain-specific assessments exist, there remains a critical gap in developing an integrated and empirically grounded framework that jointly evaluates air, water, and captures their combined influence on urban environmental quality. This study fills that gap by constructing the Composite Environmental Quality Index – Air, Water (CEQI-AW) for Delhi, using 2022–23 as the base year (Index = 100). The index facilitates both monthly and annual comparisons of environmental quality from 2022–23 onward, drawing on publicly available real-time monitoring networks, administrative datasets, and spatial environmental information.
The framework consists of three pillars: Air Quality Index (AQI), Water Quality Index (WQI). Monthly data from April 2022 to March 2023 are used to construct the base-year composite index, and subsequent months up to the latest available period are incorporated for temporal trend analysis. Air quality indicators are sourced from Central Pollution Control Board (CPCB) and Delhi Pollution Control Committee (DPCC) continuous monitoring stations and include concentrations of PM₂.₅, PM₁₀, NO₂, SO₂, CO, and O₃. Water quality parameters are compiled from CPCB’s Yamuna monitoring network, Delhi Jal Board treatment plant reports, and Central Ground Water Board (CGWB) groundwater assessments, covering indicators such as BOD, COD, DO, TDS, fecal coliform, nitrate, fluoride, and heavy metals. 
The study employs a hybrid weighting method: equal weights are assigned across the two pillars for transparency, and within each pillar, a simple geometric mean is used to construct item-level indices. The CEQI-AW is then computed for each year from the base year (2022–23) through 2024–25, enabling an assessment of inter-annual and seasonal variation.
Preliminary findings reveal that while some districts in Delhi show modest improvements in air quality during targeted winter interventions, environmental quality remains under significant strain. The year-on-year comparison for winter season (especially November, December and January) shows the highest variation in air quality in Delhi, driven by severe winter smog episodes and meteorological stagnation. Water quality exhibits distinct seasonal fluctuations, with the summer months (May and June) showing peak contamination until dilution and runoff effects during the monsoon lead to temporary improvement. Overall, the composite index exhibits an upward but uneven trajectory, heavily influenced by air quality volatility. The results highlight the need for season-specific policy interventions—winter mitigation for air pollution, summer strategies for water contamination, to effectively address environmental challenges in Delhi.