Over the last few days a south/southeasterly airflow has brought a mixture of pollution from the continent and sand from the Sahara. This has led to poor air quality over the UK and high pollution levels for some parts.
The forecast for Thursday remains moderate to high across the northwest, especially around the Wirral and Merseyside, but conditions are set to change over the coming 24 hours.
A weather front will move in from the southwest during Thursday night, bringing cleaner and fresher air for Friday.
The sunshine will appear less hazy and visibility in general will be better by the end of the week.
Although moderate levels of pollution are likely to remain in the air for a time on Friday they will continue to decline.
By Sunday low levels are expected across the whole of the UK.