It doesn't really make sense what you're saying. First you say it's not good but then you question the index. You're clearly using the AQI to base your opinion

It doesn't really make sense what you're saying. First you say it's not good but then you question the index. You're clearly using the AQI to base your opinion on? To answer the ULEZ question you should compare to not having ULEZ there, which is what the GP was talking about.