Thanks to Apoorva Mandavilli for this excellent article. Honored to be included along with so many other great colleagues.
Some highlights ...nytimes.com/2023/11/20/hea…2/ "The pandemic raged for six months before global health authorities acknowledged that it was driven by an airborne pathogen. With that revelation came another:"
Nov 21 • 5 tweets • 2 min read
1/ This #CorsiRosenthalBox is used in a soils lab that is VERY dirty (extreme conditions). After 630 hrs of operation on medium flow it retained the same CADR as initial testing prior to placement in field. We will soon do a 2nd analysis after 1,260 hours of operation. More .. 2/ After 630 hours on medium flow setting the system retained initial size-specific CADR ranging from 400 cfm to 700 cfm for particles ranging from 0.3 microns to 3 microns. respectively. Outstanding results (as we see for CR Boxes in other - cleaner - field sites).
Nov 16 • 10 tweets • 2 min read
1/ Canadian's beware. An article in Canada's National Post yesterday contains misleading information RE promotion of round-the-clock hydroxyl radical (OH) generation in homes. I have purposely not included a link here.
2/ OH radicals do not "neutralize" indoor air and should not be seen as "keeping your indoor air clean" or to "improve the air you’re breathing." OH radicals are HIGHLY reactive and lead to a wide range of chemical reaction products (by-products) in indoor air.
Oct 30 • 7 tweets • 2 min read
1/ So appreciate @DrLaPook's continued focus on the importance of indoor air quality & @60Minutes for having @linseymarr & @j_g_allen on the show to discuss the fact that COVID-19 is an airborne infectious disease & has always been despite claims of many "authorities." GR8 job!
2/ Been working on IAQ for decades, doing research & teaching many undergrad & grad engineering classes on it. But few universities even offer 1 course on indoor air quality. As @j_g_allen stated, it's largely been missing from discussions of public health. Univ's included.
Oct 14 • 6 tweets • 1 min read
1/ Just saw that a company w/ a relatively expensive air cleaner is criticizing #CorsiRosenthalBox es. I wonder why? There are more peer-reviewed journal articles on the CR-Box than their product.
2/ Critical or our @ucdavis study that showed CADR that BLOW other systems away, implying the results seem too good and need to be replicated. Would love to see their data, replicated and in a peer-reviewed journal.
Oct 11 • 11 tweets • 2 min read
A bit of preliminary data on the CR Box in the @UCDavisCOE dean's office suite - one of several in our on-campus field study. CADR & effectiveness. 1/
Effectiveness (e) is defined as 1 - Cw/Cwo, where Cw = PM2.5 concentration with the air cleaner in place and Cwo is the PM2.5 concentration without the air cleaner in place. 2/
Sep 21 • 6 tweets • 2 min read
1/ After more than 15 mos & 3,300 hours of operation this CR-Box was tested & sent to CR-Box pasture about 2 mos ago. It was just recalled (with no hesitation) for service while its replacement is going through a suite of 2-month lab testing as part of our field study. 2/ Importantly, even after 15 mos and more than 3,300 hours of actual operation this CR-Box maintains an average CADR (high flow) of about 400 cfm (for particles between 0.35 and 3 microns) w/ over 500 cfm for particles greater than 2.3 microns.
Sep 19 • 5 tweets • 1 min read
1/ The Dose Makes the (risk of) Infection
My blog entry from August 2020. Still some unknowns at that time, but the fundamentals have not changed.
corsiaq.com/2020/08/19/the…2/ If you understand that with COVID-19 we have been dealing with an airborne infectious disease for almost 4 years, the concept of inhalation dose & key parameters that define it provides a roadmap for dramatically reducing infections.
Sep 11 • 10 tweets • 3 min read
1/ On the morning of 9/11 my wife & I like so many others were shocked & horrified. My wife reminded me this morning that on that day I was emphatic that large numbers of people would also get sick and die from ...
2/ extraordinary inhalation, dermal, & hand-to-mouth exposure to dust from fallen WTC towers & combustion products thereafter. Cement dust, asbestos, toxic metals, plasticizers, flame retardants, products of jet fuel combustion, products of smoldering building materials, & more.
Sep 10 • 19 tweets • 3 min read
1/ Been hearing of some push back by school districts over fears that fan motors on CR-Boxes may overheat and be a fire hazard. This thread addresses those concerns.
2a/ Resistance on the fan motor was considered in design of the original CR-Box. Clearly, resistance is greater if just one filter is duct-taped to a fan, and I wanted to get away from that simpler concept, even though such a design can be quite effective in right-sized spaces.
Sep 3 • 4 tweets • 2 min read
1/ College students returning to dorms across North America.
Just a reminder that a "classic" 4-5 MERV-13 filter #CorsiRosenthalBox in a 220 sq. ft x 9 ft can add between 15 to 27 ADDITIONAL equivalent ACH to the space (depending on flow setting, fan, etc.). 2/ That's more than what isolation rooms in hospitals are typically designed to achieve. If the starting point before CR Box is 2 ACH, the reduction in respiratory aerosol particles will be approx 90%. If the starting point is 1 ACH then CR-Box yields approx 95% reduction.
Aug 29 • 11 tweets • 2 min read
1/ In 2020 I worked w/ @Wymelenberg & @HoomanParhizkar to develop an educational tool to help schools see the benefits of various measures for reducing COVID-19 infections in classrooms. The model, named SafeAirSpaces is found at the link below.
safeairspaces.com/safeairspaces-…2/ The model was amended pivoted around a dose-response sub-model with the expert assistance of @ProfCharlesHaas. The complete model & comparison with actual outbreak scenarios is described in this paper.
2/ As stated in the article, it is possible to address airborne infectious agents, e.g., that cause COVID-19 and influenza, as well as other pollutants that improve student and teacher health, productivity, and (thus) effective education for students.
Aug 26 • 13 tweets • 3 min read
1/ Beware - A lot of uneducated and misinformed (at best) garbage being disseminated by those who do not want others to wear masks to reduce their inhalation exposure to virus-laden respiratory aerosol particles.
2/ Masks do not act like sieves with openings too big to capture some particles or small enough to capture others. Filtration mechanisms are more complex than this and have been well defined on this medium many, many times in the past by those educated on the topic.
Jul 30 • 9 tweets • 2 min read
1/ Done looking at data for last few days and on-off experiments for today. Effectiveness = fractional reduction of PM2.5 with CR-Box on vs. before switched on (no control). With CR-Box on highest flow the effectiveness is greater than 0.98 (PM2.5 drops to < 2% of initial).
2/ In terms of background aerosol concentrations in shared air, that's like wearing an N95 mask.
On lowest flow the effectiveness is 0.79 (PM2.5 concentration drops to 21% of pre-control level. Still not bad!
Jul 21 • 6 tweets • 2 min read
1/ #CorsiRosenthalBox Effectiveness and Dynamics
We are doing long-term measurements of CR Box performance in a number of real occupied environments @ucdavis, with intermittent (every 2 months) take-down and detailed lab analysis. Here are results for one office suite. 2/ The CR box is programmed to switch on at medium setting at 8 a.m. each morning and switch back off at 5 p.m. On occasion it gets switched off and back on during the occupied day to ascertain response. The plot above shows 10-min averaged PM2.5 concentrations.
Jul 15 • 10 tweets • 2 min read
1/ Particle Emissions from #NaturalGasStoves
NG stoves is a hot issue. There is abundant & increasing literature related to NOx emissions, & impacts on health & climate change associated w/ natural gas combustion. This thread focuses only on particle emissions from gas stoves.
2/ Cooking with natural gas, including stove burners and ovens, leads to emissions of ultrafine particles (UFP).
Jul 14 • 11 tweets • 2 min read
1/ #Incense Burning
Incense use in the US is increasing. In 2018, the US incense market size was $128 M USD & is forecast to reach $281 M by 2025.
2/ Incense comes in various forms - sticks (common in the US), Joss sticks, cones, coils, rope, powders, and smudge. Numerous health impacts of exposure to incense smoke have been reported. For example, ...
May 12 • 6 tweets • 2 min read
1/ New CDC recommendation on ventilation - as equivalent ACH (eACH). Aim for at least 5 air changes each hour and upgrade to MERV-13 filters. More thoughts below.
cdc.gov/coronavirus/20…2/ It's a good start and should decrease inhalation dose of respiratory aerosol concentrations by between about 20% to 40% in many classrooms (based on my experience w/ typical starting points in schools --some w/ recirculation through MERV-13 filters already achieve 5 eACH).
Mar 29 • 21 tweets • 4 min read
Efficiency vs. Effectiveness - They are Not the Same
Over the past 3+ years there has been a sharp rise in interest related to indoor air cleaners. I have consistently seen confusion over the terms efficiency and effectiveness. This thread is about the difference. 1/
When thinking about air cleaners, make sure not to conflate efficiency and effectiveness.
An air cleaner that is intended to remove aerosol particles from indoor air can be close to 100% efficient at removing particles as they flow through the device. 2/