You will only need to pay the charge if your vehicle does not meet the minimum emission standards for that zone. The minimum emission standards are Euro 4 petrol and Euro 6 diesel, for more information on this, you can visit https://www.gov.uk/guidance/driving-in-a-clean-air-zone. Alternatively you can contact the CAZ CC either by phone on 0300 029 8888 between 08:00-19:00 Monday to Friday and Saturday 08:00-14:00 or by using the online contact form available on gov.uk.