Tong Lin, Wenfeng Huang, Beverly Guo, Peter J. McKinney, Jianshun Zhang
• Investigated NPBI effect on particle and toluene removal and by-product formation. • NPBI improves the removal of particles with a stronger effect for smaller ones. • In-space and in-duct systems relative same effect on removal of particles • Low-MERV filter efficiency benefits the most from the ionization effect. • Increase in surface deposition were observed, but no particle agglomeration. This study examined the performance of NPBI on particle removal across particle sizes, evaluates toluene removal as a representative VOC, and investigates reaction products and by-product formation. Also, it evaluated the same NPBI device in both in-duct and in-space configurations. The impact of NPBI on particle deposition, filtration efficiency, and ion-induced particle agglomeration was assessed, focusing on particles sized between 0.5 to 2.5 µm. The results demonstrated that NPBI significantly improves particle removal for particles size up to 2.5 µm, with the greatest benefit observed for smaller particles. NPBI's impact was notable for low-MERV filters such as MERV-8, where the combined efficiency of the MERV-8 filter with the ionizer matched that of a MERV-10 filter, and the efficiency of a MERV-10 filter with the ionizer was comparable to that of a MERV-13 filter. Filtration effectiveness increased over time due to enhanced filter charging. Both in-space and in-duct configurations showed similar particle removal performance. In the in-space configuration, ozone levels increased from 0.6 to 6.5 ppb during ionizer operation, though no other harmful by-products were detected. In contrast, no noticeable change in ozone levels was observed in the in-duct configuration. Across all experiments, no noticeable particle agglomeration effects were detected. NPBI modestly enhanced toluene decay, with an increase in the decay constant of 0.17 h⁻¹. These findings suggested that NPBI technology effectively enhanced particulate filtration efficiency without generating noticeable harmful by-products, making it a viable solution for improving indoor air quality without increasing the pressure drop across particulate filters.