Assessing coordinated multi-pollutant mitigation and balanced economic development in urban agglomerations using a hierarchical multi-objective optimization model

Urban agglomerations face growing pressure to reconcile economic growth with coordinated control of multiple pollutants. To support regional environmental planning, this study developed a three-stage multi-objective hierarchical optimization model (TMHOM) and applied it to the Pearl River Delta urban agglomeration. Based on life cycle assessment, production-stage carbon, nitrogen, and phosphorus (CNP) emissions were quantified for major products and linked to city-level production activities. By integrating regional aggregated control, urban internal allocation, intercity adjustment, and rolling-horizon optimization, TMHOM was used to evaluate long-term emission-reduction pathways together with intercity development equity. Results showed that emissions peaked around 2023 and declined thereafter under the optimized pathway. By 2030, total output value increased by 51.06%, while total CNP emissions decreased by 20.23% and emission intensity declined by 47.19%, indicating a decoupling of economic growth from environmental pressure. Beyond emission control, the optimized pathway suggested that conditional reallocation of energy-related and industry-related production from core cities to mid-sized cities could improve regional balance and reduce the concentration of environmental burdens, subject to adequate receiving-city capacity. Scenario comparison further showed that the full three-stage framework provided a more balanced performance across emission reduction, output growth, and regional equity, while sensitivity analysis confirmed its robustness under plausible market fluctuations. The study provides a quantitative decision-support framework for coordinated multi-pollutant control and sustainable development in rapidly urbanizing regions.