| In recent years, the Pearl River Delta(PRD) region has experienced severe photochemical smog pollutions characterized by high levels of ozone, arsing from its rapid urbanization and industrialization. The nonlinear relationship between ozone and its precursors Volatile Organic Compounds(VOCs) and Nitrogen Oxides(NOx) which associated with meteorological conditions, emission distributions and land use types has made ozone become one of the focuses in regional air pollution control work.A methodological framework for systematically characterizing the nonlinear relationship between ozone and its precursors was established including comparison of model-ready source profiles, chemical mechanisms and study on the Empirical Kinetics Modeling Approach. This framework was applied to analyze the relationship between ozone and its precursors, characterize the ozone formation regime and evaluate the impacts of different precursor reduction ratios on ozone control.First, based upon chemical speciated source profiles of major VOCs sources in the PRD region, i.e., on-road mobile source, industrial solvent usage source and non-industrial solvent usage source, local model-ready source profiles of the CB05 and the SAPRC-07 chemical mechanisms were developed and compared with the USEPA SPEICATE. Results showed that:(1) under the SAPRC-07 chemical mechanism, differences between local and USEPA SPECIATE profiles in different sources were more significant than CB05;(2) local and SPECIATE profiles were generally consistent in shoe-making industry, furniture-making industry, gasoline light duty vehicles and motorcycles,(3) while obvious discrepancies were observed in PCB-manufacturing industry, light-duty diesel vehicles, LPG taxis and nonindustrial solvent usage source.On the basis of model-ready source profiles, potential influences between major chemical mechanisms on the modeling performance were considered and then local source profiles were compared with SPECIATE profiles. Results showed that:(1) modeling results using the CB05 mechanism were easier to reproduce the ozone variation and(2) using local profiles can be helpful for capturing ozone values.Second, ozone isopleths in typical areas on elevated and normal ozone days were established based upon monitoring pollutant concentrations, city characteristics, land use types and different emission reduction combinations comprehensively. Ozone isopleths were applied to identify the nonlinearity of ozone and its precursors and characterize the ozone formation in typical areas under different pollutant conditions. Results showed that there were temporal and spatial differences in the ozone formation regimes during severe polluted days:(1) for typical urban areas in Guangzhou and Foshan as well as industrial areas in Shenzhen and Dongguan, the ozone formation regime appeared to be borderline in precursor limitation, leaning toward NOx limitation in summer while more VOC limitation in autumn;(2) for suburban areas in the vicinity of Nanshan, the ozone pollution was mainly VOC-limited in both seasons;(3) for rural areas in the southwest of Jiangmen, the ozone was much equated with NOx-limited in summer and become borderline in autumn.Finally, the ozone response to different precursor reduction combinations was investigated based on ozone isopleths on elevated ozone days. Due to the complicated relationship of O3-VOCs-NOx, none of reduction combinations had overwhelming advantages than others. Results in this study showed that among the three reduction ratios of precursors, the ratio of 1:2 and 3:1(VOC/NOx) are the optimal options in theory for ozone reduction in summer and autumn, respectively, while the ratio of 1:1(VOC/NOx) may be more applicable for ozone control in the PRD region when taking feasibility into consideration. |
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