Greening the Atmosphere: Sustainable PM2.5-O3 Compound Pollution Control in a Coastal Industrial City of the Yellow River Delta

Urban air pollution is shaped by the combined influences of emission changes, meteorological variability, and socioeconomic development. This study examined the temporal and seasonal variations in major air pollutants in Dongying, China, from 2019 to 2024 and explored their associations with selected meteorological, socioeconomic, and urban-development indicators. Grey Relational Analysis (GRA), based on five annual observations from 2019 to 2023, was used to quantify temporal similarities between pollutant concentrations and eight selected indicators. The robustness of the GRA rankings was further assessed using alternative distinguishing coefficients and leave-one-year-out sensitivity tests. Distinct temporal and seasonal patterns were observed among the pollutants. PM2.5 exhibited its highest seasonal mean concentration in spring (54.88 μg m−3), a pattern that may be partly associated with enhanced regional dust transport and dust-storm activity. Winter PM2.5 concentrations also remained elevated, consistent with the possible combined influence of heating-related emissions and unfavorable atmospheric dispersion. By contrast, SO2 reached its seasonal minimum in autumn, which may reflect reduced heating-related emissions together with relatively favorable dispersion conditions. The GRA results revealed pollutant-specific temporal associations with the selected socioeconomic and urban-development indicators. Construction floor area ranked highest for PM2.5 in the baseline analysis, indicating the strongest temporal similarity among the indicators considered and suggesting possible associations with construction-related fugitive dust, material handling, and upstream building-material production. Motor-vehicle ownership ranked highest for O3, although this association was less robust in the leave-one-year-out sensitivity analysis. Seasonal variations in PM2.5 and O3 were also consistent with changes in meteorological conditions, atmospheric dispersion, photochemical activity, and emission characteristics. Unlike the predominantly winter-centered particulate-pollution patterns commonly reported for northern inland cities in China, Dongying showed pronounced spring and autumn co-occurrences of elevated PM2.5 and O3, indicating distinctive seasonal characteristics in this coastal petrochemical environment. The relatively low frequency of co-elevated PM2.5-O3 days during 2022–2024, despite continued GDP growth, further indicates that economic expansion and air-quality improvement may occur concurrently under evolving industrial structures, energy mixes, and pollution-control regimes. These relationships are observational and should not be interpreted as evidence of independent causal effects or quantitative source contributions. Overall, the findings extend current understanding of PM2.5-O3 pollution dynamics in coastal industrial environments and provide observational support for season-specific, multi-pollutant air-quality management strategies.