Abstract
Ozone (O3) pollution has become the major new challenge after the suppression of PM2.5 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.
Highlights
The Pearl River Delta (PRD), the largest city cluster in South China, has long suffered from severe air pollution due to rapid urbanization and intensive anthropogenic activities
We found that global Moran’s I index (GM) values were almost constant regardless of fluctuations in meteorological conditions
The results show that stations with similar O3 levels aggregated distributed more in PRD
Summary
The Pearl River Delta (PRD), the largest city cluster in South China, has long suffered from severe air pollution due to rapid urbanization and intensive anthropogenic activities. There has been insufficient investigation into the relationships between O3 and meteorological conditions in the perspective of space, especially the long-term spatiotemporal evolution Meteorological variables, such as solar radiation, can control the photochemical reaction and affect net O3 production directly, while high temperatures are conducive to O3 production by increasing emission of natural sources biogenic volatile organic compounds (BVOCs), hydroxyl radical (OH) concentrations in the atmosphere, and decomposition of peroxyacetyl nitrate (PAN) [29,30,31]. The aggregated distribution of stations affected by local impacts will be strengthened when non-local sources are added It is unclear whether the aggregation is affected by meteorological conditions, areas with high precursor levels are more sensitive to meteorological variations [35].
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