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Aerosols cut winter ozone but raise it in summer

Aerosol haze over China changes ozone in opposite directions in January and July by altering mixing and sunlight.

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What two ADE pathways on ozone are isolated?

Changes in atmospheric dynamics (∆Dynamics) and changes in photolysis rates (∆Photolysis).

Which months represent winter and summer?

January and July 2013.

How is model ozone evaluated?

Against observations from 74 cities on China’s urban air-quality platform.

What is the winter combined ADE impact on daily-max ozone?

An overall reduction across China by up to 39 μg m−3.

What is the July combined ADE impact?

Surface daily-max ozone increased by up to 4 μg m−3, mainly from dynamics.

How does winter northern China ozone chemistry respond to extra NOx from a stable PBL?

VOC-limited: extra NOx enhances NO titration and inhibits ozone.

How does July chemistry differ?

Most of China is NOx-limited, so extra NOx from ADE-induced stability facilitates ozone formation.

Did including ADEs improve ozone bias?

Yes: they moderately reduced the January high bias and July low bias in most regions.

When does ozone correlate negatively with PM2.5 in winter?

When PM2.5 exceeds 120 μg m−3, strong ADE suppression of ozone appears.

What process analysis tools were used?

Integrated process rates (IPRs) for seven modeled processes and integrated reaction rates (IRRs) for gas-phase ozone chemistry.

Which heterogeneous chemistry is present but not quantified for ozone here?

N2O5 hydrolysis and related aerosol uptake of NOx/HO2.