Stick to Proven Technologies for Air Cleaning in Schools: The case of ionization technologies

Posted on by jvincent

We’ve been getting a lot of inquiries from school leaders, parents and others about how to clean the air inside schools. As we’ve written about, too many schools have stale and stagnant indoor air, which as we all now know is a recipe for COVID-19 spread.

ASHRAE and others have very clear and solid guidance for cleaning indoor air – from sophisticated mechanical solutions to simple inexpensive ways to improve natural ventilation. This visualization of ventilation patterns in a classroom, created by the New York Times, is really helpful in understanding how air moves inside classrooms with students and teachers present.

We implore school leaders to follow these recommendations, particularly ASHRAE’s – they are a leader in the field and base their recommendations on rigorous research. Much of that research comes from decades of work, but others come from brand new research in response to COVID-19.

The key for school leaders is to STICK TO PROVEN TECHNOLOGIES. Do not waste your school district’s precious and limited resources on unproven technologies.

Ionization technology in one such technology. Despite claims made by some companies, the peer-reviewed research on their effectiveness finds little evidence that they clean much air (especially in real world settings). The California Department of Public Health's September 2020 paper, THE ROLE OF BUILDING VENTILATION AND FILTRATION IN REDUCING RISK OF AIRBORNE VIRAL TRANSMISSION IN SCHOOLS, ILLUSTRATED WITH SARS-COV-2, states specfiically, "Do not use air cleaning devices that generate harmful pollutants (i.e., ionization devices or ozone generators), or devices of unproven effectiveness" (page 3).

A colleague from a national organization working with school districts from across the country emailed us saying:

“I have heard of LEAs considering purchasing ionization air cleaners, among a whole host of other options to improve facilities (all anecdotal)… I think a lot of vendors are looking at these federal funds as an opportunity to market their products and solutions to districts to address COVID-19 and safely reopen schools. Our members are being inundated with a lot of proposals from companies.”

But perhaps more importantly, there is evidence that introducing ions into the air can be harmful to people.

This Mother Jones interview with Delphine Farmer, an atmospheric chemist at Colorado State University who is currently studying bipolar ionization, is really useful. Are Schools’ Fancy New Air-Scrubbing Devices Really Effective—and Safe? A scientist airs her concerns about the surge of products that supposedly kill airborne viruses.

This Twitter thread on electronic air cleaning systems (including ionization) by Marwa Zaatari, member of the ASHRAE Epidemic Task Force, is especially informative.

Bottom line: the evidence of the benefits and/or harms of ionization technology to clean indoor air is very mixed as of now. Scientists strongly recommend sticking to proven technologies. See below:


Lastly, here are three brand new peer-reviewed studies on ionization technology. All three find that evidence that ionization devices, negative or bipolar, are “playing chemistry with the indoor air” and may result in significant adverse health effects.


Evaluating a commercially available in-duct bipolar ionization device for pollutant removal and potential byproduct formation. Yicheng Zeng, Prashik Manwatkar, Aurélie Laguerre, Marina Beke, Insung Kang, Akram Ali, Delphine Farmer, Elliott Gall, Mohammad Heidarinejad, Brent Stephens. Building and Environment, 2021.
Negative ions offset cardiorespiratory benefits of PM2.5 reduction from residential use of negative ion air purifiers. Liu W, Huang J, Lin Y, Cai C, Zhao Y, Teng Y, Mo J, Xue L, Liu L, Xu W, Guo X, Zhang Y, Zhang JJ. Indoor Air, 2021. doi: 10.1111/ina.12728
Different cardiorespiratory effects of indoor air pollution intervention with ionization air purifier: Findings from a randomized, double-blind crossover study among school children in Beijing. Dong W, Liu S, Chu M, Zhao B, Yang D, Chen C, Miller MR, Loh M, Xu J, Chi R, Yang X, Guo X, Deng F. Environmental Pollution, 2019.  doi: 10.1016/j.envpol.2019.113054


A far wiser bet is to avoid “additive” technologies until there is an independent body of research supporting their safety and efficacy. Instead, stick to proven air cleaning technologies for now - we know they work: add air cleaning filters (e.g., ASHRAE MERV 13 rated or higher) and using AHAM CADR rated portable air cleaners.

School Reopening & Ventilation: Which California Schools Will Get Priority for AB 841 Funds to Upgrade their Building Ventilation Systems?

Posted on by Jeff Vincent and Mona Al-Abadi

DISCLAIMER: This blog discusses AB841 and provides an initial analysis to identify the schools likely to be eligible for funding priority. AB 841 funds are being administered by the California Energy Commission's California Schools Healthy Air, Plumbing, and Efficiency Program (CalSHAPE). For the most up-to-date info, visit the program's website: Make no mistake about it: safely reopening schools amidst the COVID-19 pandemic requires that our school buildings have adequate fresh air ventilation and/or filtration to reduce transition risk. It is not the only mitigation measure needed, but it is an essential one. Why? Because COVID-19 is a respiratory virus that spreads…

School Facility Funding is the Most Inequitable Aspect of California Education Finance: Why do the two new school bond bills barely tackle it?

Posted on by jvincent

by Jeff Vincent, co-founder and director of public infrastructure initiatives at CC+S. Will school buildings be safe and healthy enough for my kids to return to school? That’s the key question millions of parents across the country and California are asking. Our awareness of the indoor spaces we enter these days, amidst COVID-19, is elevated. As it should be. The virus that causes COVID-19 is respiratory and highly transmittable through the air. Indoor spaces with numerous people and little or no fresh air ventilation or filtration are the riskiest places to be. A conundrum we collectively face is that this describes many, many of our public school…

New CC+S Study: Are California Public School Kitchens Scratch-Cooking Ready?

Posted on by jvincent

A new Center for Cities + Schools study in collaboration with Conscious Kitchen and The Edible Schoolyard Project. One way to serve healthier school meals is by incorporating “scratch-cooking” techniques, whereby many or most of the ingredients are prepared onsite from a raw and/or minimally processed form, into school food service programs. However, the vast majority of public school kitchens across the U.S. and in California are not designed and/or equipped to scratch cook. Raw and/or unprocessed food ingredients have shorter shelf lives and fewer added preservatives, thus requiring specialized kitchen infrastructure and equipment for receiving, storing, and preparing. To understand…

California School Bonds on the November 2020 Ballot: Are they equitable?

Posted on by Jeff Vincent and José Lopez

By Jeff Vincent and José Lopez, Center for Cities + School at UC Berkeley   In each California election, there are sure to be school bonds on local ballots across the state. November 3, 2020 is no different: 55 school districts have general obligation (G.O.) bonds for school facilities revenue going before voters. Two districts – Gonzales USD in Monterey County and River Delta Joint Union SD in Sacramento County – each have 2 bonds before voters. In total, there is just under $12 billion in local bond authority going before voters across the state to modernize and construct public…

Y-PLAN Peninsula Students Lift Up Affordable Housing Proposals, Their Client Facebook is Listening

Posted on by Tira Okamoto

Redwood City, Menlo Park and East Palo Alto high school students involved in Y-PLAN, an action research initiative based at the UCB Center for Cities+Schools, are making media headlines as their Project Client Facebook unveils a $1 million dollar accessory dwelling unit project in response to the students’ affordable housing proposals. In print, on air, and on TV screens, Y-PLAN student scholars are sharing their stories as young planners making change in their communities. The Peninsula is facing a rapid increase in housing costs. With rising rents and home prices, long-term residents, who are often people of color, are at…

To Live in the Community You Serve: School District Employee Housing in California

Posted on by Sean Doocy

Faced with high turnover and a shortage of qualified teachers, California school districts are aggressively adopting new strategies to recruit and retain teachers and staff. A prominent and ambitious strategy is employee housing assistance – particularly direct creation of new rental housing. Employee housing strategies by school districts have emerged as a direct response to the housing affordability crisis in California (for both rental and ownership). The housing affordability crunch is most acute in employment-rich coastal urban areas like Los Angeles and the Bay Area. Across California, school districts, local governments, state governments, private developers, nonprofits, and foundations have taken…

Opportunity Zones Should Help Modernize Public School Facilities

Posted on by Mary Filardo and Jeff Vincent

Mary Filardo, 21st Century School Fund Jeff Vincent, Center for Cities and Schools In 2017, we founded [Re]Build America’s School Infrastructure Coalition (BASIC), a non-partisan coalition to advocate for a ten-year $100 billion investment as part of the nation’s critical infrastructure package. But reducing inequity in our nation’s public school facilities will take a variety of tools. These tools are needed at the local, state, and federal levels. Could the new federal Opportunity Zone Program help modernize public school facilities in low income communities? One of the provisions of the Tax Cuts and Jobs Act of 2017 was the creation of “Opportunity Zones” (OZs). Opportunity Zones are structured to provide…

School as Anchors of Diversity

Posted on by Kfir Mordechay

Across the metropolises of the United States, gentrification is making neighborhoods hardly recognizable. In a short time, what was once a minor force of urban change, gentrification is now sweeping through many cities like a tsunami. By some estimates over the last 15 years, nearly 20 percent of neighborhoods in the 50 largest cities have experienced major gentrification. From New York to Los Angeles, there has been a large influx of middle class families. Some have even begun to do what had long been unthinkable in the post-war decades of white flight from central cities to the suburbs; enroll their…

TOWERS OF POWER: Snapshot of a Future I Want To Inhabit

Posted on by Shirl Buss, PhD.

I am an urban designer and educator.  One of the most joyful things I do is facilitate architecture and urban planning studios for elementary school children in public schools through Youth in Arts and UC Berkeley’s Y-PLAN. Like many adults today, I am asking myself how—in my professional role—can I positively contribute to the #MeToo movement for and with the children in my life? How might I, when I work with young people, respond proactively to the gender inequities and injustices that we are witnessing every day?  How can I help both boys and girls express their own power, free from the…