Evaluating air cleaner effectiveness in schools: a comprehensive review and protocol of a cluster-randomized controlled trial of physicochemical and microbial markers - Esmée Rianne Janssen; Kimberly J. Linde; Marcel G. L. C. Loomans; Wietske Dohmen; Lützen Portengen; Lili Xia; Jan F. L. Diepens; Dick J. J. Heederik; Twan van Hooff; Inge M. Wouters; Lidwien A. M. Smit (Frontiers in Public Health, 2026)