The positive difference Glasgow’s LEZ is already making

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Guest blog from Andrew Malby, Senior Specialist Scientist at SEPA.

On 1 June 2023, Phase 2 of Glasgow’s Low Emission Zone (LEZ) began to be enforced by Glasgow City Council following its introduction on 31 May 2022. The LEZ will improve air quality by discouraging non-compliant vehicles from entering the zone. The LEZ will be enforced through Penalty Charge Notices for the owners of any vehicle being driven in the zone that does not meet Euro 6/VI emission standards for diesel vehicles or Euro 4/IV for petrol vehicles.

This follows a period of five years since the introduction of Phase 1 of Glasgow’s LEZ (bus only) when the bus fleet has been required to meet annual incremental targets to improve emission standards, now reaching 100% EURO VI compliance. Full details of the Glasgow LEZ can be found at

Evidence from 2019 indicated that the number of hours each year when nitrogen dioxide (NO2) concentrations peaked above 100 µg/m3 (micrograms [one-millionth of a gram] per cubic meter air) along a major bus corridor in the city centre were decreasing. This coincided with an increase in the proportion of Euro VI buses on city centre routes.

Air quality across Glasgow and elsewhere was then impacted by the COVID-19 lockdown when baseline traffic levels were substantially reduced. However, bus fleet improvements continued during this time, and now that 100% of bus journeys are fully compliant with the LEZ emission standards there have been further reductions in the number of high hourly peaks of air pollution.

In 2022 the air quality monitoring station on Hope Street recorded an annual average nitrogen dioxide concentration of 39 µg/m3. Except for 2020 when traffic was affected by the lockdown this was the first year it met the annual average* air quality objective for nitrogen dioxide of 40 µg/m3. However, the wider monitoring network indicates that improvements in air quality following Phase 1 of Glasgow’s LEZ are focused on bus corridors, and improvements are now required in all areas of the city for all vehicle classes. This will be achieved with Phase 2 of the LEZ now in force which applies to all other vehicle types except motorcycles/exempted.

The design of Glasgow’s LEZ was finalised by close partnership working between SEPA, Glasgow City Council, Transport Scotland, and relevant stakeholders. The initial stages involved collecting detailed traffic data to understand the different types of vehicles that travelled through the city, including information about their age and emissions of air pollutants.

Computer models were then used to estimate how much air quality could be improved by excluding those vehicles which emit the most air pollution. The models also simulated how traffic movements might change following the implementation of the LEZ. This evidence from SEPA’s air quality models supported the design of the LEZ boundary and the types of vehicles that would be compliant with LEZ emission standards.

SEPA also provided bus operators with online bus data tools to help them maximise their investments in having the cleanest buses within the LEZ and to place these buses on routes where the biggest improvements in air quality were required. Prior to the implementation of the LEZ less than 20% of bus journeys through the zone were made by Euro VI buses, although this was less than 10% on some routes. Operators have now achieved 100% compliance using technology to reduce emissions from existing vehicles and by replacing older buses with new, lower emission and electric vehicles. For example, on Hope Street around 60% of journeys are now made by electric buses.

SEPA will continue to work with Glasgow City Council during ongoing LEZ monitoring where changes in the vehicle fleet on key routes will be regularly assessed. SEPA are also exploring collaboration with academic partners to report on changes to air quality that can be linked to improvements in the vehicle fleet.

The air quality and bus fleet data described here can be explored through an interactive data tool developed by SEPA, available via the link below:

LEZs were introduced to Aberdeen, Dundee, Edinburgh and Glasgow in May 2022, and Glasgow’s LEZ began enforcement on 1 June 2023. Grace periods apply for the other three cities before enforcement begins 30 May 2024 for Dundee and 1 June 2024 for Aberdeen and Edinburgh.

Check if your vehicle is compliant using our vehicle checker here.

*Annual mean