Current
petrol: Euro 1
diesel: Euro 5(PM) (Euro 4 with a diesel particulate filter only when the Euro 5 PM standard is met)
Bi-fuel diesel-gas: Euro 3

passenger cars 1 October 2019 (others 1 October 2020)
petrol: Euro 2

1 October 2021 (others 1 October 2022)
petrol: Euro 3
diesel: Euro 6

1 October 2024 (others 1 October 2025)
petrol: Euro 4
diesel: Euro 6 purchased before 31.01.2018

1 October 2027 (others 1 October 2028)
petrol: Euro 5
diesel: Euro 6 purchased after 31.01.2018

1 October 2029 (others 1 October 2030)
diesels: are banned up to and including Euro 6D. This would mean diesels are likely to be banned. It may potentially be that if Euro 7 diesel exists by then it may be permitted into the Area C. Further clarification will be given when available.

1 October 2030
petrol: Euro 6

are given below. The dates for "others" such as residents, taxis, buses... are in each case 1 year later (see here for further details).