Low-cost sensors can be very relevant for FAIRMODE, especially concerning methodologies to combine sensor networks with modelled data and official measurements. Present experiences suggest important roles for data fusion/assimilation approaches, and possibly other techniques with similar scopes. WG6 activities will focus on discussing and understanding the strengths and weaknesses of the different ways low-cost sensors can be used in conjunction to modelling. The focus points are:

• 1 Exchanging best practices about the calibration and subsequent integration of sensor network data in air quality mapping methods (data fusion) and demonstrating the use of sensors in different areas/countries with national models to fuse
• 2 Providing guidance and recommendations on the use of sensors (e.g. citizen science projects), both in terms of calibration, data fusion or communication about related uncertainties
• 3 Exploring how exploitation and validation of an air quality sensor network can contribute to improved air quality modelling, with a focus on city applications.