Ozone (O₃) pollution has become the major new challenge after the suppression of PM_2.5 to levels below the standard for the Pearl River Delta (PRD). O₃ can be transported between nearby stations due to its longevity, leading stations with a similar concentration in a state of aggregation, which is an alleged regional issue. Investigations in such regional characteristics were rarely involved ever. In this study, the aggregation (reflected by the global Moran’s I index, GM), its temporal evolution, and the impacts from meteorological conditions and both local (i.e., produced within the PRD) and non-local (i.e., transported from outside the PRD) contributions were explored by spatial analysis and statistical modeling based on observation data. The results from 2007 to 2018 showed that the GM was positive overall, implying that the monitoring stations were surrounded by stations with similar ozone levels, especially during ozone seasons. State of aggregation was reinforced from 2007 to 2012, and remained stable thereafter. Further investigations revealed that GM values were independent of meteorological conditions, while closely related to local and non-local contributions, and its temporal variations were driven only by local contributions. Then, the correlation (R²) between O₃ and meteorology was identified. Result demonstrated that the westerly belonged to temperature (T) and surface solar radiation (SSR) sensitive regions and the correlation between ozone and the two became intense with time. Relative humidity (RH) showed a negative correlation with ozone in most areas and periods, whereas correlations with u and v were positive for northerly winds and negative for southerly winds. Two important key points of such investigation are that, firstly, we defined the features of ozone pollution by characterizing the temporal variations in spatial discrepancies among all stations, secondly, we highlighted the significance of subregional cooperation within the PRD and regional cooperation with external environmental organizations.

Industrial biomass boilers (IBBs) are widely promoted in China as a type of clean energy. However, they emit large amount of volatile organic compounds (VOCs) and the emission characteristics and the underlying factors are largely unknown due to the sampling difficulties. In this study, three wood pellet-fueled and two wood residue-fueled IBBs were selected to investigate the characteristics of VOCs emissions and to discover their underlying impacting factors. The emission factor of VOCs varied from 21.6 ± 2.8 mg/kg to 286.2 ± 10.8 mg/kg for the IBBs. Oxygenated VOCs (OVOCs) were the largest group, contributing to 30.3%-73.6% of the VOCs emissions. Significant differences were revealed in the VOCs source profiles between wood pellet-fueled and wood residue-fueled IBBs. Operating load, excess air, furnace temperature and fuel type were identified as the primary factors influencing VOCs emissions. The excess air coefficient should be limited below 3.5, roughly corresponding to the operating load of 62% and furnace temperature of 630 °C, to effectively reduce VOCs emissions. VOCs emissions also showed great differences in different combustion phases, with the ignition phase having much greater VOCs emissions than the stable combustion and the ember phases. The ozone formation potential (OFP) ranged from 4.3 mg/m³ to 31.2 mg/m³ for the IBBs, and the wood residue-fueled IBBs yielded higher OFP than the wood pellet-fueled ones. This study underscored the importance of OVOCs in IBB emissions, and reducing OVOCs emissions should be prioritized in formulating control measures to mitigate their impacts on the atmospheric environment and human health.