Literature round-up

Literature round-up: June 2015

It’s been forever since I’ve done one of these literature round-up posts, but you could say that about a lot of post types on here….

Regardless, here are a few recently published papers that I find really interesting:

  • Ji and Zhao, 2015, PLoS ONE, Estimating Mortality Derived from Indoor Exposure to Particles of Outdoor Origin – this is a really important effort to combine outdoor air pollution data (PM2.5 and PM10) with a mechanistic understanding of how outdoor particles infiltrate into indoor environments (where we spend most of our time) and estimate the impact of indoor exposure to particles of outdoor origin on mortality. Basically: in the US, Europe, and China, our indoor exposures to outdoor PM account for about 80 or 90% of the mortality associated with outdoor PM. This is something I’ve been thinking about and saying for several years now, so I love to see the work that Bin Zhao and his group are doing at Tsinghua University!
  • Bouslimani et al, PNAS, Molecular cartography of the human skin surface in 3D – This one is intense — basically, our bodies are literally covered with both chemicals and microbes, but the chemical makeup of skin surfaces aren’t well understood in total. This paper swabbed the hell out of some peoples’ skin and performed mass spectrometry (for the chemicals) and 16S rRNA sequencing (for the microbes) and made a 3D map of the data. They ended up with some wild human chemical/microbial plots like this:


  • Langevin et al, Building and Environment, Simulating the human-building interaction: Development and validation of an agent-based model of office occupant behaviors – This is very cool work that develops and validates an agent-based model of occupant behavior using data from a long-term field study in an office. Basically the ‘agents’ in the model can reasonably accurately mimic the real life occupants and make decisions about whether or not to turn on a fan, heater, or open a window based on their current thermal comfort levels and sensations. This is really important work to see published.
  • Jiao et al, ES&T, Field Assessment of the Village Green Project: An Autonomous Community Air Quality Monitoring System – cheap air quality sensors, low cost air quality monitors, or whatever you want to call them are HUGE right now. It really seems like people want to know what they’re breathing and want to be able to understand it accurately and inexpensively. It’s a sort of holy grail for any field. This paper reports a field assessment of a solar-powered air monitoring park bench that could measure ozone, PM2.5, and meteorological parameters and stream the data to the public. They were able to collect a bunch of data in Durham, NC, and had relatively decent correlations with nearby federal equivalent method (FEM) monitors (in English: regulatory monitors). Very cool.

20 papers every BERG student should read

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.

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Energy and environmental literature round-up, November 2013

I haven’t posted one of these literature round-ups since June. The last one was right before I post in which I said “I’m going to start blogging more!” That turned out to be completely false, but now that our semester is wrapping up, I thought I’d try to jump back in! So here are a few recent papers related to building science, energy, environment, and health that have sparked my interest:

  • Improving airflow measurement accuracy in VAV terminal units using flow conditioners – A good friend and colleague of mine Michael Waring at Drexel recently published an article with coauthors on using a simple flow conditioner to make airflow measurements in HVAC systems more accurate, reducing errors from 10-45% (depending on nearby elbows and kinks) to about 5%.
  • Human exposure to airborne particulate matter leads to oxidative DNA damage
  • Both soil and paint contributes to lead levels in Australian homes
  • Particle size distributions form e-cigarettes – Always controversial, this team measured particle concentrations and particle size distributions in mainstream smoke from electronic cigarettes under a range of liquid flavors, liquid nicotine contents, and “puffing times.” Particle size distributions peaked around 120-165 nm, similar to conventional cigarettes. Resulting particle concentrations were actually higher than a conventional cigarette. Flavor didn’t matter.
  • Meta-analysis of high penetration renewable scenarios – A meta-analysis of several studies evaluating the possibility, operability, and implications of high levels of renewable sources of electricity in grid scale power systems shows that in most regions, renewable sources can provide the majority of a country’s or region’s electricity demand, at least on an hourly scale.
  • Systemic and vascular effects of circulating diesel exhaust particulate matter – Diesel exhaust particles (DEPs) were shown to increase inflammatory responses when they enter the bloodstream. Also, DEPs were shown to be quickly sequestered in the spleen and liver in mice.
  • Fine particulate matter from urban areas was shown to generate a higher reactive oxygen species (ROS) response than rural and/or coarse PM – responses were independent on PM chemical composition.
  • Fine and ultra fine particle decay rates in homes – Using time-resolved data over the course of 1 week in 74 homes in Edmonton, CA, Wallace et al. used concentration peaks and subsequent decay periods of both PM2.5 and submicron particles (representative mostly of ultra fine particles), to estimate decay rates. Median and interquartile decay rates were 1.08 per hour (IQR: 0.62-1.75 per hour) for PM2.5 and 1.26 per hour (IQR: 0.82-1.83 per hour) for submicron particles. Air exchange contributed about 25% of these values, on average. Window opening, home age, use of central furnace fans and kitchen/bathroom exhaust fans, use of air-conditioners, use of air cleaners, and indoor-outdoor temperature differences all influence these values.
  • Diversity and distribution of fungi on residential surfaces – Rachel Adams and coauthors sampled fungi from 3 surfaces in homes: drains in kitchens and bathrooms, sills beneath condensation prone windows, and the skin of human occupants. Weedy genera and a large set of fungi likely of outdoor origin were found on the window sills; human foreheads contained a surprising amount of plant pathogens. Indoor fungal richness was generally high, but the authors conclude that most fungi were unlikely to be growing on the surfaces but are more likely to have been deposited/settled from other sources.
  • Asthma and the diversity of fungal spores in air – many studies in the past have found correlations between asthma symptoms and exposure to fungi indoors; this short article highlights some of that past work and suggests that by doing more species identification we will be able to learn more about which fungi species contribute to asthma and inflammation
  • Low fungal diversity in house dust is associated with childhood asthma development – Somewhat contrary to the previous paper, a new study of low-income children whereby house dust was collected at age 1 and asthma status determined 6 years later. Although the study had a small sample size of 13 cases and 28 controls, decreasing fungal diversity within the genus Cryptococcus was significantly associated with increased asthma risk. No fungal taxon (species, genus, class) was positively associated with asthma development. Hmm…
  • PVC flooring at home and development of asthma in young children – Last article on asthma this time… in a 10-year follow up study of children in Sweden revealed that children who had PVC floorings in their bedroom at baseline (when hey were 1 to 5 years old) were more likely to develop asthma during the following 10 year period than compared to children without PVC flooring. Exposure to PVC flooring – and the phthalate plasticizers emitted – during pregnancy may be critical to development of asthma in children later on.

Literature round-up: Improving assessments of indoor exposures to outdoor air pollution

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.


Literature round-up, December 2012

Well, I had grand visions of posting links to new literature that I find interesting on a more regular basis than I have been doing. I was shooting for monthly posts, but the last time I posted was back in September! Better late than never I suppose.

Here are a few studies that I’ve come across over the last few months that will hopefully spark some interest:

  • Study on economic impacts of energy service companies – Interesting study on the economic impacts of energy service companies (ESCOs). ESCOs are generally private companies that operate on a model of selling energy performance upgrades to building owners whereby the building owners are motivated to do so because of they are promised long-term energy savings. This study shows that the ESCO industry continued strong growth even through the recession. Additionally, energy payback times are getting longer, suggesting that low-hanging fruit is being plucked in these areas and that more complex (and more expensive) systems with longer rates of returns are being utilized more (Energy Policy).
  • Factors influencing variability in infiltration of PM2.5 – Wonderful paper dissecting a bunch of indoor-outdoor airborne particle measurements that were made in and around about 40 homes in Canada a few years ago. This same team reported their initial findings in several recent papers, but this one tries to explain why some homes had far higher or lower indoor levels of outdoor PM2.5 and ultrafine particles (UFPs). These folks do great work and they show that (quite intuitively) window-opening behaviors, presence and operation of HVAC systems and filters, and the age of homes predicted a good portion of the variation across homes (Atmospheric Environment).
  • Household light makes global heat – This study presents some new lab and field measurements of kerosene wick lamps, which are a significant source of particulate matter emissions, including black carbon (BC), particularly in developing regions of the world. They show tremendously high emission rates of BC, which makes kerosene lamps important in terms of climate forcing and an important contributor to global warming. We’ve already  known a lot about the health and climate impacts of cookstoves in developing regions, but this makes one more important combustion source that needs to be reckoned with. (Environmental Science and Technology).
  • Size and concentration of droplets generated by coughing in human subjects – I’ve been working on a project for the National Air Filtration Association over the last few weeks attempting to quantify what types of effects HVAC filtration may have on the transmission of infectious airborne diseases. In doing so, I’ve come across a few really interesting articles (I’ve already blogged about one of those). In my review, I’ve learned about the aerosols that are expelled from our bodies when we breath, speak, cough, or sneeze. There’s actually a surprising lack of information on the concentrations and sizes of these emitted particles, but this study did a fine job of measuring the particle size distributions of expelled droplets from about 50 human subjects. Very interesting stuff and extremely important for understanding how disease (including influenza and the common cold virus) is transmitted. These researchers showed that a large majority of the droplet nuclei (a fancy word for droplets that have been expelled and then had surrounding liquid evaporated) exist within the 0.7 to 2.1 µm size range (Journal of Aerosol Medicine).

Literature round-up, September 2012

I dig through a lot of literature on air quality (indoors and outdoors), environmental exposures, health effects, as well as energy use, energy efficiency, energy policy, not to mention other scientific and engineering miscellanea. I will try to post links to papers that I find interesting to this blog on a semi-regular basis (shooting for monthly, but we’ll see).

So, for the month of September, I’ve come across the following interesting papers:

  • Residential radon and lung cancer in a Danish cohort – A study of almost 60000 Danish people over ~20 years tracked lung cancer incidence and looked for associations between incidence and modeled radon concentrations in their homes (lots of uncertainty there). Found a slight increased risk for each 100 Bq/m3 (about 2.7 pCi/L), but confidence intervals were very wide, so no statistical significance (Environmental Research).
  • Exposure to VOCs and lung function/heart rate variability in urban cyclists – A study of about 40 healthy Canadian cyclists biking for an hour on either high or low traffic roads was conducted. VOC samples were collected via SUMMA canisters and analyzed by GC-MS; lung function was measured using exhaled nitric oxide (which is a kind of tracer for lung function) and exhaled breath volume; and heart rate variability was measured at the last 5-minutes of each study period. 26 VOCs were identified, but propane, butane, ethane, isoprene, and benzene were those significantly associated with the various health outcomes (Environmental Research).
  • Household mold and allergens and asthma symptoms – A study of about 1200 homes with 5-10 year old children in Connecticut collected spot samples of indoor airborne fungi (later analyzed via agar plate) and allergens in house dust (later sampled by enzyme-linked immunosorbent assay for dust mite, cat, dog, and cockroach allergens). The children kept a diary of asthma symptoms (e.g., times of wheeze, use of medication, etc.) for about a month. The study found significant associations between (a) fungi (Penicillium) and increased wheeze, cough, and asthma severity; (b) pet allergens (dog and cat, although cat at much lower concentrations) and increased cases of wheeze; and (c) cat and dust mite allergens and increased use of asthma medication (Environmental Research).
  • Home dampness, children’s genetic polymorphisms, and asthma – A study about about 6000 school children in Taiwan surveyed parents (via questionnaire) about their children’s asthma and wheeze symptom frequency, as well as the presence of dampness, visible mold, and mildewy odors in their homes. The study also collected mouth swabs of the children, which were analyzed using realtime PCR to detect specific genetic polymorphisms previously known to be linked to asthma. Their analysis shows that children exposed to dampness and mildewy odors at home were more likely to be awakened at night with wheeze symptoms if they carried a specific genetic polymorphism (Environmental Research).
  • Indoor air quality in day cares – A study of about 20 day care centers in Canada measured temperature, relative humidity, carbon dioxide, VOCs (via SUMMA canisters), and formaldehyde in conjunction with surveys of building characteristics and operation. From the measurements and surveys, the study concludes that CO2 concentrations were often quite high (a sign of inadequate ventilation) and that the presence of a mechanical ventilation system, as well as more play area per child (bigger spaces), were associated with lower CO2 levels. But the presence of a mechanical ventilation system alone wasn’t as good of a predictor of indoor VOC levels as CO2 levels, suggesting that it’s better to know more about the actual building’s mechanical system operation than the mere existence of a system. Fair enough (Environmental Research).
  • Penetration of fine particles through rough cracks – A lab study setup a small facility with known crack geometries to simulate airflow through an idealized leak in a building’s exterior wall with different surface roughnesses. This general idealized penetration work has been performed before, and although idealized, this kind of work offers good insight into the material, leak, and flow characteristics that impact particle penetration through envelope cracks and gaps. This study added to these by looking not only at smooth surfaces, but by then installing sandpapers of different roughness characteristics. Their findings showed that the level of roughness didn’t much matter, but that the presence of any roughness at all (versus smooth surfaces) made more particles deposit, particularly those in the ultrafine range (Atmospheric Environment).
  • Modeling impacts of US vehicle emissions standards on ozone and PM2.5 – A modeling study by ENVIRON International estimated the potential impacts of light-duty vehicle emissions standards in the U.S. on outdoor air quality, including concentrations of ozone and particulate matter (PM2.5) in the eastern U.S. through 2022. The study predicts that transitioning from “Tier 1” to “Tier 2” standards could reduce daily maximum 8-hour ozone concentrations 14% and maximum 24-hour PM2.5 by 9%. These “tiers” were part of the Clean Air Act Amendments of 1990. Tier 1 vehicles were phased in through the 1990s, and basically included six different emissions categories for vehicles based on weight. Tier 2 vehicles were phased in over the end of the 2000s and included different metrics. The whole tier system is somewhat complex, but here is an idea of what emissions are controlled under the various tiers. Basically, emissions of NOx, organics, CO, PM, and formaldehyde are controlled. Limiting NOx and organics (VOCs) help add to the reductions in ozone predicted by this study (NOx + VOC lead to ozone formation in complex photochemistry), and the PM restrictions directly result in the predicted lower PM2.5 concentrations (Atmospheric Environment).
  • Review of toxicity of ambient particulate matter in terms of size, source, and chemical composition – A really good review of previous studies of ambient particulate matter and health effects, particularly looking at the relative impacts of different sizes, sources, and chemical composition of PM. Basically, there is some evidence out there now that traffic-related PM emissions show some degree of higher toxicity than other constituents (traffic-related constituents include file and ultrafine particles, some metals, and elemental carbon). But overall, this review describes the need for more work with stronger programs involving toxicology and epidemiology in conjunction with better estimates of size, source, and composition of PM (Atmospheric Environment).
  • Building energy simulation: impact of surrounding buildings versus stand-alone buildings – A study used EnergyPlus to simulate ~20 residential buildings as if they were standing alone without any surrounding buildings (something we often do in energy modeling but something that is rare or nonexistent in actual urban environments) or if they were part of a network of other homes in a neighborhood. They simulated buildings in an extreme hot (Miami) and cold (Minneapolis) climate. They found that in both climates, energy used for cooling is greatly over-predicted in the single-building analysis versus the network-analysis (by up to ~60%!), primarily due to shading by other buildings that goes unaccounted for in the single-building analysis. In the cold months in the cold climate, single-building analysis actually under-predicted energy use versus the neighborhood analysis, probably again due to shading (i.e., solar gain helps reduce heating loads in a stand-alone building, lowering the estimate of energy req’d; solar gain is blocked in a network analysis (Building and Environment).
  • Zero peak electric housing – This study used ESP-r to model the possibility of eliminating electrical power draws from a home during the hours of peak demand on the electric grid. It’s a really good concept and this study explores first the use of efficiency and energy-saving measures to reduce demand at peak hours, then looks at what kind of solar PV integration would be necessary to get to zero peak demand. They conclude that almost 50% could be met by architectural design, equipment efficiency, and occupant behavior measures. The rest could be met by a small PV and battery system (Building and Environment).
  • Indoor air quality in commercial reference buildings – The good people at NIST published a study on a bunch of indoor air quality modeling (using CONTAM) for a series of commercial buildings that can be used as reference or “typical” commercial buildings. They modeled indoor CO2, VOCs from indoor sources, and indoor ozone and PM2.5 from outdoor sources. Provides a good reference for others to use in case studies (Building and Environment).
  • Intake fraction for the indoor environment – This study used the metric “intake fraction,” which is a measure of what fraction of a pollutant emitted in a particular environment actually enters a human body (via inhalation, ingestion, or dermal exposure). Indoor sources have much higher intake fractions than outdoor sources because we spend so much time indoors and are in such close contact with indoor sources. So for every gram of a pollutant emitted indoors, more enters our bodies than a gram of the same pollutant emitted outdoors. This study advanced work on intake fractions to explore a suite of typical indoor-generated compounds (with different physical characteristics) released into the air, or from carpets, or from vinyl surfaces. This helps guide exposure assessment by showing the relative importance of types of indoor surfaces for different compounds in terms of exposure to adults and humans (Environmental Science and Technology).