Following a policy change by The Scottish Government to align ambient particulate matter (PM) pollution with the WHO guidelines (Scottish Government, 2015) a review to help inform this change was commissioned. This showed amongst other results, the ratio of PM2.5/PM10 was lower at 0.63 compared with the national (UK) average of 0.7, this was used to derive an estimated PM2.5 from measured PM10. Although some methods used in this study and in the UK technical guidance were similar, the difference in these ratios would help Scotland in achieving of Air Quality Strategy (AQS) objective of 10 μg m-3. It was recommended from this research that an expansion of the PM2.5 monitoring network be instigated and that the introduction of Local Air Quality Management Areas for PM2.5 be considered.