# Extreme heat exacerbates atmospheric ozone pollution: Holistic data-based causal investigation in China

## TL;DR

Extreme heat causes increased ozone pollution in China, requiring combined climate and air quality strategies.

## Contribution

A three-step causal inference framework confirms extreme heat's causal role in ozone pollution.

## Key findings

- Extreme heat significantly elevates ozone levels nationwide in China.
- Causal influence flows from extreme heat to ozone in most provinces.
- Integrated climate adaptation and ozone control policies are urgently needed.

## Abstract

Climate change-induced extreme heat (EH) events intensify atmospheric surface ozone (O3) pollution, posing growing threats to public health and environment. To address the lack of rigorous empirical confirmation regarding the causal impact of EH on O3 despite their observed co-occurrence, this study develops a robust statistical framework to assess this relationship across China. The framework integrates three checkpoints: (1) correlational checkpoint based on linear mixed model; (2) causal checkpoint based on instrumental variable, Heckman two-step selection model, and propensity score methods with generalized bootstrap validation; and (3) directional (of causality) checkpoint based on transfer entropy. Results consistently demonstrate a statistically significant causal effect of EH on elevated O3 levels, with the dominant influence flowing from EH to O3 nationwide and across most provinces in China. These findings support integrated air quality management and climate adaptation strategies, guiding policy interventions to mitigate the compound risks of EH and O3 pollution.

•A three-step causal inference framework for extreme heat and ozone is developed•Extreme heat is a causal driver of elevated ozone pollution across China•Causal effect is confirmed nationally and in most Chinese provinces•Findings necessitate integrated climate adaptation and ozone control policies

A three-step causal inference framework for extreme heat and ozone is developed

Extreme heat is a causal driver of elevated ozone pollution across China

Causal effect is confirmed nationally and in most Chinese provinces

Findings necessitate integrated climate adaptation and ozone control policies

Earth sciences; Atmospheric science