4.3.4. The Impact of Related Environmental Policies

During our sample period, some environmental regulatory policies occurred in China, which may affect carbon emissions. To eliminate the impact of these environmental policies on city carbon emissions, in this section we will further control the effect of these policies.

Two major environmental regulatory policies were instituted during the sample period. The first is the Clean Air Action policy (CAA) in 2013. Following Zhu and Xu (2022), we manually collect cities' air pollution targets and generate the variable CAA [5]. Following Zhu and Xu (2022), we measure CAA: CAA = Ln(air pollution targets) \* Post(year ≥ 2013) [5]. Adding CAA variables to the baseline model (1), the result is shown in column (4) of Table 5. The Treat\*Post is still significantly negative with the city carbon emissions (LnCO2), suggesting that the basic conclusion is robust even if we control the effect of the Clean Air Action policy on city carbon emissions.


**Table 5.** Other robustness check of the effect of city cluster policy on CO2 emissions.

Note: *t* statistics are shown in parentheses; \*\*\* represent significance at the 1% levels, respectively.

The second is the provincial carbon emissions trading policy implemented in 2013 http://www.tanpaifang.com/tanjiaoyi/2012/0219/41.html (accessed on 5 May 2022). We set a policy dummy variable CET that equals one if the province is eventually included in the carbon emission system list by the end of our sample period, and zero otherwise. Adding CET variables to the baseline model (1), the result is shown in column (5) of Table 5. The Treat\*Post is still significantly negative with the city's carbon emissions

(LnCO2), suggesting that the basic conclusion is robust even if we control the effect of carbon emissions trading policy on city carbon emissions.

Finally, we control the impact of both the Clean Air Action (CAA) and the carbon emissions trading policy (CET). The result in column (6) of Table 5 shows that the core explanatory variable Treat\*Post is still significantly negative with the city carbon emissions. Although considering the interference of these two environmental regulatory policies, the city cluster policy can still significantly reduce the city carbon emissions.
