By Brent Stephens on February 15, 2015
My colleague Michael Waring, who directs the Indoor Environment Research Group at Drexel University, recently shared a thought with me. He was thinking about compiling a list of about 20 papers that every graduate student in his group should read and be very familiar with. It’s a great idea, so here I am doing the same.
Below is a list of 20 papers I think every Built Environment Research Group student (BERGer) should read. Narrowing to only 20 papers is tough. In fact, this may forever be considered a rough draft of a list, and it will most certainly change or expand over time. But I have chosen these articles to span a wide range of topics related to energy and air quality in the built environment, including the physics or chemistry of indoor air pollutants, human exposure to indoor pollutants and health effects, and energy efficiency in buildings. There may be other even better articles on each topic, but these were chosen for their combination of impact on research and thought in their areas of inquiry, the usefulness of their methods, their clarity in presentation, and for the references included within them as well as their links to other papers that have referenced them upon publication.
Continue Reading →
Filed under: Building science | Doing research | Energy efficiency | Environmental health | Experimental methods | Exposure measurement | Indoor air pollution | Infectious disease | Literature round-up
By Brent Stephens on November 6, 2013
This post was originally written for microBEnet and is copied here.
First of all, Happy Halloween everyone. I think my costume this year will be a blogger!
For those that don’t know me, I’m Brent Stephens, an assistant professor in the Department of Civil, Architectural and Environmental Engineering at Illinois Institute of Technology in Chicago, IL. I call my research team the Built Environment Research Group and my teaching and research interests are primarily in characterizing energy and air quality in buildings. Some people would also call me a “building scientist,” and it’s that description that brought me to microBEnet. Since Fall 2012, my team and I have been working with Jeff Siegel at the University of Toronto on Jack Gilbert’s Sloan-funded Hospital Microbiome Project. Continue Reading →
Filed under: Doing research | Experimental methods | Local to Chicago | Student awesomeness
By Brent Stephens on June 11, 2013
Much of my work over the last few years has been focused on improving methods to assess our indoor exposures to outdoor airborne pollutants. This is driven in part by the fact that we spend so much time indoors (and so much time at home) and that different pollutants can infiltrate indoors in different ways; at the end of the day, much of our exposure to outdoor air pollution actually ends up occurring indoors. Another motivator is that there are wide variations in some of the fundamental drivers of indoor proportions of outdoor pollutants, particularly in homes, that I don’t think have been captured very well to date. Air exchange rates are certainly higher in leakier buildings and we understand how to model these fairly well (although not as well as you might think), but good data on envelope penetration factors in a large number of homes are limited. We also don’t know a ton about HVAC filtration, system runtimes, indoor deposition rates, and the least academic yet probably most difficult of all to assess: window opening behaviors.
With all that said, we’re working on a handful of projects (and have a few related proposals under review) that would work to improve our knowledge of some of these drivers (as well as our predictive ability). Also, I noticed a couple of papers out in the Journal of Exposure Science and Environmental Epidemiology that continue to move this kind of work forward. I thought I’d share them here.
1. Breen et al. (2013) published a review of the models that can be used to estimate air exchange rates in buildings. They review driving forces (e.g., I/O temperature differences, wind speed, and mechanical ventilation) in conjunction with the leaks/openings through which driving forces can force airflow. Then they review a handful of models with varying levels of details and input parameter needs for estimating air exchange rates in buildings. They finish up with a list of advantages and disadvantages of each method and describe ongoing research needs. This is a very helpful paper for understanding how airflow can be assessed and ultimately used to impact exposure assessment for epidemiology.
2. Hodas et al. (2013) published a study where they used existing epidemiological data for myocardial infarction (heart attack) associations with elevated outdoor particulate matter (PM2.5). However, instead of using only outdoor concentrations, they accounted for variations in indoor proportions of PM2.5 across a variety of homes (related to the paper above!), as well as for time spent at home, in order to explore whether or not accounting for indoor exposures altered the outcome (accounting for differences in air exchange rates only). Interestingly, they didn’t observe differences in the exposure-response outcomes for those with different air exchange rates in their homes, but primarily because they used data from a “case-crossover” study whereby occupants are their own controls. That is to say that they track the same occupants in time with different exposures; therefore, it makes sense that indoor proportions of outdoor PM2.5 may be always consistent within a particular group, so building factors are in a sense controlled for in each “case”. They did however observe differences in the relative odds for heart attack for those in leakier homes, as occupants of leakier homes (with higher air exchange rates and thus higher indoor proportions of PM2.5 that would otherwise have not been accounted for using central site data). They conclude with “These ?ndings also illustrate that variability in factors that in?uence the fraction of ambient PM2.5 in indoor air (e.g., AER) can bias health effects estimates in study designs for which a spatiotemporal comparison of exposure effects across subjects is conducted.” Very much a motivator for the work we’re doing!
3. Baxter et al. (2013) actually preceded the study above by comparing the performance of a few different models for predicting indoor proportions of outdoor PM2.5 in homes — the models largely vary by the way they account for different air exchange rates in homes (related back to the first study here). Again, results suggest that differences in residential exposures may be important for epidemiology studies, and importantly, not captured by outdoor monitors alone. These kinds of studies again motivate me to get out there and develop better ways of assessing some of the inputs to these models (which are not always captured well) with our knowledge of building science to ultimately inform epidemiology studies and improve our decision making for regulatory purposes.
Filed under: Experimental methods | Exposure measurement | Literature round-up | News | Particulate matter
By Brent Stephens on December 13, 2012
I have been spending much of my time recently working on a project for the National Air Filtration Association (NAFA). The goal is to review literature on the transmission of infectious diseases and explore what kinds of impacts that HVAC particle filters may have on the transmission of infectious aerosols. It’s a wonderfully interesting project that I’m happy to be working on. But it has also sent me digging into a world of literature that I previously didn’t know existed.
For example, I’ve known that there has been a long running debate about whether infectious diseases are transmitted primarily via (i) inhalation of airborne aerosols, (ii) contact with contaminated surfaces, or (iii) some imprecise mixture of the two. In digging in this field, I came across a paper today that details an amazingly absurd, yet extremely helpful, set of experiments.
Check out the following statement from Dick et al. (1987). Aerosol Transmission of Rhinovirus Colds. The Journal of Infectious Diseases. 156(3):442-448:
Twenty-seven to 34 men >18 years of age were inoculated intranasally with 560-2400 TCID50 of safety-tested RV16 [i.e., rhinovirus, or a virus that leads to the common cold] by pipette and spray on two successive days. On the third day, eight men with the most severe colds (donors) played stud and draw poker with 12 antibody-free … men (recipients) between the hours of 8 a.m. and 11 p.m.
In experiments A-C the donors and six of the 12 recipients played cards naturally and used cloth handkerchiefs for secretion, cough, and sneeze control, whereas the remaining six recipients in each experiment wore devices that blocked completely all hand-to-head movements.
Did you catch that? A group of men were taken into a lab and injected with cold virus. Then the following day, those men were put together in a room with 12 healthy uninfected men where they played stud and draw poker all day long! The catch was that half of those healthy men were able to touch their faces and behave quite normally; the other half were restrained by these braces such that they couldn’t touch their faces!
This is such an absurd but beautifully constructed experiment to me. I don’t even know if you could get IRB approval for something like this any more. I can just imagine the conversation that led to this experiment. “What if we take a bunch of people, infect them, then make them play poker for 12 hours. Half the people they play poker with can blow their nose, touch their faces, etc., and the other half will be physically restrained — but only to the point where they can’t touch their face… they can still play cards!
In the end, their results are extremely important to the debate on airborne vs. surface transmission of disease. They reported no significant difference between the two groups, suggesting that aerosol transmission must have been the dominant route. Amazing!
Filed under: Experimental methods | Exposure measurement | Infectious disease | Particulate matter
By Brent Stephens on August 24, 2012
Earlier this summer I wrote an article for the summer 2012 issue of Air Media, a publication by the National Air Filtration Association (NAFA). NAFA and its members have been wonderful, accepting supporters of my work. Many members have become friends, and I always enjoy helping out the filtration industry by collaborating with NAFA and its body of members.
You can read my article, “Field Measurements of Filtration Efficiency in Homes,” on page 4 of the current issue. In it I discuss how to perform measurements of particle removal efficiency by HVAC filters in real residential indoor environments and highlight some recent test results.
I really appreciate Al Veeck (of NAFA) and Jim Rosenthal (of Tex-Air Filters) for reaching out and asking me to write this article, as well as my PhD adviser Dr. Jeffrey Siegel for his large contribution to this work.
View Air Media online or download a PDF of the article directly
Filed under: Experimental methods | News | Particulate matter | Publication
By Brent Stephens on May 3, 2012
I posted a link on Twitter the other day (April 30) about a study investigating the inhalation exposure to formaldehyde from the use of personal care products (i.e., lotions, conditioners, shampoos, etc.). Basically, the study involved using a relatively large amount of several products in a simulated bathroom and measuring the resulting concentrations of formaldehyde. In their interpretation of their results, they said:
“Overall, our data yielded evidence that inhalation of FA [formaldehyde] from the use of PCP [personal care products] containing FA-releasers poses no risk to human health.”
I posted the link, then thought about the study a day later, wondering about its methods. So I dug a little deeper, and found the methods and results to be somewhat misleading, depending on your point of view.
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Filed under: Experimental methods