Correlations between PM_2.5 and Ozone over China and Associated Underlying Reasons

• Main Authors: Jia Zhu, Lei Chen, Hong Liao, Ruijun Dang
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Atmosphere
• Subjects: PM_2.5; ozone; correlation; temperature
• Online Access: https://www.mdpi.com/2073-4433/10/7/352

We investigated the spatial-temporal characteristics of the correlations between observed PM_2.5 and O₃ over China at a national-scale level, and examined the underlying reasons for the varying PM_2.5&#8722;O₃ correlations by using a chemical transport model. The PM_2.5 concentrations were positively correlated with O₃ concentrations for most regions and seasons over China, while negative correlations were mainly observed in northern China during winter. The strongest positive PM_2.5&#8722;O₃ correlations with correlation coefficients (<i>r</i>) larger than +0.7 existed in southern China during July, and the strongest negative correlations (<i>r</i> &lt; &#8722;0.5) were observed in northern China during January. It was a very interesting phenomenon that the positive PM_2.5&#8722;O₃ correlations prevailed for high air temperature samples, while the negative correlations were generally found in cold environments. Together, the effective inhibitory effect of PM_2.5 on O₃ generation by reducing photolysis rates and the strong titration effect of freshly emitted NO with O₃ contributed to the strongest negative PM_2.5&#8722;O₃ correlations in northern China during January (i.e., in cold environments). The strongest positive correlations in southern China during July (i.e., at high temperature), however, were mainly attributed to the promoting effect of high O₃ concentration and active photochemical activity on secondary particle formation.