aspg-38-4533-1793997058 20261106203058 American Scientific Publishing Group admin@americaspg.com American Scientific Publishing Group Journal of Sustainable Development and Green Technology JSDGT 2836-5399 2026 6 2 Adam Marks Higher Education Leadership Academy, Dubai, United Arab Emirates Two allocations can give the same mean reduction in fine particulate matter (PM2.5) and still leave different cities above the reference concentration. We examine this choice with 2021 records for 40 Spanish cities from the World Health Organization’s January 2024 database. The model minimises population-weighted squared excess above 5 µg/m3 subject to a resource budget, local reduction caps and an optional minimum share for each city, and numerical optimisation confirms its analytical solution. At half of assumed total capacity, optimal allocation and proportional allocation both bring the weighted mean concentration down from 9.882 to 8.404 µg/m3; optimal allocation cuts squared excess loss by 9.44% and between-city excess variance by 83.39% relative to proportional allocation. A minimum share of one-quarter of each local reduction cap extends reductions to every city above the reference concentration and raises squared excess loss by 3.01%. A separate feasibility test puts a common concentration ceiling of 10 µg/m3 within reach at 17.12% of assumed total capacity. A ceiling of 9 µg/m3 would push one city past its local reduction cap. These conditional planning results set targets for later assessment of specific interventions. 2026 53 61 4533 https://creativecommons.org/licenses/by/4.0/ 10.54216/JSDGT.060206 https://americaspg.com/journal/38/article/4533 https://americaspg.com/storage/articles/manuscripts/01M6PY4SZ6R7YG4341DMF7MD4Z.pdf