| Summary: | We investigated the spatial-temporal characteristics of the correlations between observed PM<sub>2.5</sub> and O<sub>3</sub> over China at a national-scale level, and examined the underlying reasons for the varying PM<sub>2.5</sub>−O<sub>3</sub> correlations by using a chemical transport model. The PM<sub>2.5</sub> concentrations were positively correlated with O<sub>3</sub> concentrations for most regions and seasons over China, while negative correlations were mainly observed in northern China during winter. The strongest positive PM<sub>2.5</sub>−O<sub>3</sub> 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> < −0.5) were observed in northern China during January. It was a very interesting phenomenon that the positive PM<sub>2.5</sub>−O<sub>3</sub> correlations prevailed for high air temperature samples, while the negative correlations were generally found in cold environments. Together, the effective inhibitory effect of PM<sub>2.5</sub> on O<sub>3</sub> generation by reducing photolysis rates and the strong titration effect of freshly emitted NO with O<sub>3</sub> contributed to the strongest negative PM<sub>2.5</sub>−O<sub>3</sub> 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 O<sub>3</sub> concentration and active photochemical activity on secondary particle formation.
|
|---|
