Negative ions offset cardiorespiratory benefits of PM2.5reduction from residential use of negative ion air purifiers

Negative ion air purifiers (NIAPs), as a less costly alternative to the HEPA filtration, have been increasingly deployed in China and potentially elsewhere. While reducing indoor concentrations of fine particulate matter (PM2.5), NIAPs generate massive amounts of negative ions that may be of health concern. We performed week-long interventions with NIAPs in the dormitories of 56 healthy college students living in Beijing. In a randomized order, each student underwent a true and a sham NIAP session. Cardiorespiratory outcomes were measured before and after each session. The use of true NIAPs reduced indoor PM(2.5)concentrations significantly, while notably increased negative ion levels. Increases in PM(2.5)and negative ion (NI) exposure were independently associated with increased urinary concentration of malondialdehyde, a biomarker of systemic oxidative stress, resulting in a null net effect of NIAP on malondialdehyde. Likewise, no significant net effects of NIAPs were observed for other outcomes indicative of lung function, vascular tone, arterial stiffness, and inflammation. Our findings suggest that negative ions, possibly along with their reaction products with the room air constituents, adversely affect health. The downsides do not support the use of NIAPs as a health-based mitigation strategy to reduce PM(2.5)exposure, especially in residences with PM(2.5)concentrations that are not extremely high.

Automated summary

The study found that while the use of negative ion air purifiers (NIAPs) can reduce indoor particulate matter concentrations, it also increases negative ion levels and urinary concentration of malondialdehyde, a biomarker of systemic oxidative stress. There were no significant net effects of NIAPs on various health outcomes related to lung function, vascular tone, arterial stiffness, and inflammation, indicating that the downsides of using NIAPs do not outweigh the benefits in reducing PM2.5 exposure.