Trend in chemical components and sources of PM2.5 and its relationship with ozone in central PRD, China (2018–2023)

Dongguan, a global manufacturing hub and megacity in the central Pearl River Delta (PRD), China, faces challenges in balancing air quality improvement with economic growth. The dynamic changes in PM_2.5 and their coordination with ozone provide a crucial basis for air quality policy-making, and are applicable to other fast-developing cities worldwide. This study analyzed trends in PM_2.5 composition, sources, and interactions with ozone from 2018 to 2023. While PM_2.5 decreased significantly (3.76 μg m⁻³ yr⁻¹) along with its inorganic components (SO₄²⁻, NO₃⁻ and NH₄⁺, ranging from −0.57 to −0.34 μg m⁻³ yr⁻¹), secondary organic aerosol (SOA) conversely increased (+0.18 μg m⁻³ yr⁻¹). Source analysis revealed that a secondary organic factor based on the positive matrix factorization (PMF) method also showed a rising trend, although notable uncertainty remains. Industrial emissions increased annually with statistical significance (+0.17 μg m⁻³ yr⁻¹). A non-linear relationship between PM_2.5 and ozone was identified, with co-occurrence below 40 μg m⁻³ PM_2.5 and apparent suppression of ozone above this threshold, accompanied by elevated NO₃⁻, NO_x and NO₂/NO ratios. Our results highlight the urgent need to control secondary pollutants and their precursors such as NO_x and VOCs, particularly from industrial sources.