资源环境科技发展态势分析平台

PM_2.5 and O₃ controls are traditionally considered separately because PM_2.5 is usually high in winter while O₃ is generally high in summer. In this study, we explore the opportunity of controlling the two pollutants simultaneously through a better understanding of their intra-seasonal correlation and chemical-coupling behaviors under different meteorological conditions during the late summer and early fall (August–September) episodes in the San Joaquin Valley (SJV), California. A correlation analysis is first used to identify the temporal correlations between O₃ and PM_2.5 and their underlying physical and chemical drivers. Sensitivity analysis is then applied to determine the chemical coupling between PM_2.5 and O₃ and subsequent multipollutant control opportunities under two contrasting meteorological conditions using the Community Multi-Scale Air Quality (CMAQ) model. We find that O₃ and PM_2.5 are positively correlated on the daily timescale because both are sensitive to atmospheric stagnation. However, O₃ and PM_2.5 are negatively correlated on the hourly timescale determined by the negative correlation between hourly NO₃⁻ and O₃, which is mainly due to the opposite effects of T and RH on the diurnal variations of NO₃⁻ and O₃. Reducing NO_x on average lead to O₃ increase, but it can facilitate reducing O₃ at higher O₃ (>75 ppb) locations under the more stagnant conditions. NO_x emission control could become beneficial for both O₃ and PM_2.5 when the NO_x emissions in 2005 are further reduced by 15% under the more stagnant meteorological conditions and by 30% under the more ventilated meteorological conditions.