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The air isn't usually this bad. But it has gotten worse recently. Photo Courtesy of Los Angeles Metro Archive.

Air Quality

Air Filters Used In LA Schools Linked To Higher Test Scores

NYU Assistant Professor of Economics Michael Gilraine studied what happened when a number of schools in the Los Angeles area had air filters installed as a safety measure after a very large natural gas leak occurred. Gilraine’s research uncovered an unexpected benefit, and he answered some questions about his research for CleanTechnica.

Air pollution is a very serious threat to human health. Each year, hundreds of thousands of premature deaths are linked to this global problem. Various illnesses result as well. Another problem, but one that typically receives less attention, is cognitive decline. A number of research studies have come out in recent years documenting this link. It’s very obvious, if not extremely so, that intelligence is central to human functioning at all levels of human societies.

Los Angeles air pollution

Photo courtesy of Los Angeles Metro Archive.

Without it, we wouldn’t last long. So, when we also begin to figure out that not only does air pollution cause a vast amount of damage to our physical well-being, it also harms our mental capacity, this very deleterious impact should be taken quite seriously.

NYU Assistant Professor of Economics Michael Gilraine studied what happened when a number of schools in the Los Angeles area had air filters installed as a safety measure after a very large natural gas leak occurred. The 2015 Aliso Canyon gas leak had many parents and school administrators concerned about how the potential exposure might impact children in schools. A number of schools had air filters installed to prevent this exposure. Gilraine’s research uncovered an unexpected benefit, however. He answered some questions about his research for CleanTechnica.

How many schools received the air filters?

A. A total of 18.

What kind of air filters were used and how much did they cost?

A. Costs were around $700 per filter and it seems 1,756 filters were delivered. I spent a decent amount of time trying to get the exact plug-in air filter they used. Unfortunately, SoCalGas was the entity that purchased the air filters and so LAUSD had no documentation on it and SoCalGas was unwilling to share due to the ongoing litigation. I also emailed several principals, who confirmed they received the filters, but were unsure on the exact model (one said they had the filters still in storage, so if I flew out to LA I could likely figure it out…).

I can definitely tell you that the plug-in air purifiers came from the following list of filters that the California Air Resource Board approved for the leak. Indeed, according to a press release from BlueAir, SoCalGas purchased 210 of the Blue Air filters on that list in early January 2015, making me think that they likely put those filters in the schools (in fact, that number is the exact same as the number of air filters delivered to Granada Hills High School) but I cannot confirm that is the exact model used as SoCalGas could have ordered filters from multiple companies. The key (according to an someone who knows air filters who I talked to) is that they appeared to have purchased filters with a reasonably deep carbon layer in addition to its HEPA particle filter.

How old were the students in those schools at the time?

A. The main analysis is restricted to elementary schools (and grades that were tested by the state standardized tests), so really covers grades 4 and 5 (9-11). Some supplemental analysis looked at middle schools (grades 6-8) although there were very few middle schools in the area, making it tough to draw conclusions.

What, in a lay person’s view, does this figure mean.. can it be converted to a percentage increase?

“…air filter exposure led to a 0.20 standard deviation increase in mathematics and English scores.”

A. The 0.20 standard deviation test score increase is around the same found in a (quite well-known) RCT run in the late-1980s called Project STAR that reduced class sizes from (around) 22 to 15 students.

Converting standard deviations into percentage gains are tough as the percentage gain depends where the student is in the distribution. For a news article on a prior research project of mine, I converted test score gains into months of learning. The 0.20 standard deviation gain would be roughly two and a half months of extra learning. I have also seen these numbers put in terms of test score gaps, such as black-white test score gap.

How did you establish a correlation between air filter installation and increased academic scores?

A. Since air filters were just installed in schools within five miles of the gas leak, the basic idea is to compare test score growth in the year the air filters were installed for schools just within five miles of the leak (and thus receive air filters) and those just outside (who do not).

Were the air filters installed in individual classrooms or at the level of the central HVAC system?

A. Plug-in air filters were delivered. These were put in every classroom, office, and common area in every school within five miles of the leak. In addition, these schools also had active carbon filters installed in their HVAC systems if they did not already have them.

What pollutants were removed from the schools’ indoor air?

A. A bit unclear as I do not have detailed pollution measures within the schools (they did test the air within schools, but this testing mostly focused on methane). These air filters are supposed to eliminate particulate pollution (e.g. dust, pollen) and VOCs (e.g. methane).

Was any gas from the leaks detected in the schools?

A.  There is no strong evidence of abnormally high methane levels according to air quality testing done in the schools. The LAUSD did evacuate two schools very near the leak (<2 miles), however, and these schools did seem to have relatively high methane levels (these students were relocated to schools about 7 miles from the leak). These schools were not included in the analysis (indeed, they did not receive filters).

Were any measurements taken related to physical health, like noting a reduction in respiratory illness or asthma, as well?

A. No

Do you think schools with polluted indoor air are potentially experiencing student cognitive issues due to the exposure?

A. This study, along with other excellent work by Sefi Roth, and Claudia Persico, seems to suggest so.
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