William Nazaroff, PhD – Pollutant Dynamics in Indoor Air and Exposure Science

Air Date: 12-2-2016|Episode 439

This week we welcome one of the top IAQ researchers in the world William “Bill” Nazaroff, PhD. Dr. Nazaroff is a Daniel Tellep Distinguished Professor at the University of California Berkeley and has served as a Faculty Senior Scientist at Lawrence Berkeley Laboratory…

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This week we welcome one of the top IAQ researchers in the world William “Bill” Nazaroff, PhD. Dr. Nazaroff is a Daniel Tellep Distinguished Professor at the University of California Berkeley and has served as a Faculty Senior Scientist at Lawrence Berkeley Laboratory. His research centers on air quality engineering, emphasizing two themes: pollutant dynamics in indoor air and exposure science.  On the first, his primary interest is to better understand the physics and chemistry that control the concentrations, fates, and effects of pollutants in indoor environments.  On the second topic, he and his group apply basic knowledge about air pollutants to build a quantitative and mechanistic understanding of the relationship between emissions from sources and consequent human exposures.  His group pursues research through a combination of laboratory and field experiments, modeling, and data analysis.  In recent years, in addition to maintaining vigorous activities in the two primary areas, he has had a growing concern about and interest in the themes of sustainability, climate change, and energy-use efficiency.  He has recently been pursuing research opportunities in these newer thematic areas, especially when opportunities arise that intersect with his primary research themes.

Z-Man’s Blog:

Pollutant dynamicist

William Nazaroff, PhD is one of the top IAQ researchers in the world. Dr Nazaroff is the Daniel Tellep Distinguished Professor at the University of California, Berkeley and has served as a Faculty Senior Scientist at Lawrence Berkeley Laboratory. A dynamacist is a person who investigates and researches. Bill describes himself as a “pollutant dynamicist”. His IAQ interest piqued in 1978, beginning with an undergraduate research assistantship on radon and energy efficiency. Radon poses the greatest radiation exposure risk to the public. Interest in radon has declined in the scientific community due to attained understanding.  But it’s still an important practical problem to address.

Nuggets mined from today’s episode:

What IAQ issue receives the attention it deserves? 

No issue in IAQ gets the attention it deserves.

Please tell listeners what is meant by the pollutant dynamics of indoor air?Think about the composition of air in buildings.  What are the physical, chemical, and biological processes that control this composition?  That’s pollutant dynamics.  As a scholar, I want to improve our understanding of this system.  As an engineer, I’d also like to build knowledge about how best to control it.

What do people commonly assume about the pollutant dynamics of indoor air that is wrong?

Among the few who give it any thought, a key challenge is finding the right balance between complexity and simplicity.  A quote from Einstein applies: “make the thing as simple as possible, but not simpler.”  Indoor air quality has vast unexplored richness and complexity.  At the same time, physical laws still apply: energy is conserved, material is conserved, the ideal gas law holds.

How much do the pollutant dynamics of indoor air quality change by type of building? In other words is it different in residential vs. commercial and institutional buildings?

At the most fundamental level, the dynamics don’t change: gas molecules and airborne particles don’t have a clue what kind of building they occupy.  What does matter, though, is the set of processes that are important.  So, when we make the system “as simple as possible” what we include and exclude can vary a lot with building type.  One example: mode of ventilation (natural + infiltration in residences vs mechanical in commercial and institutional).  Another example: indoor pollutant sources, which can vary considerably across building classes.

What is a key concept about pollutant dynamics of indoor air that you would like to be sure all IEQ consultants understand?

Maybe the best response to this question is to point to an editorial I wrote for Indoor Air, “Four principles for achieving good indoor air quality.”  (Vol 23, pages 353-356, 2013, freely available for download at the journal website).  I posed the question: do we know enough to articulate simple rules for achieving good indoor air quality?  The (trial set of) rules are four principles expressed in 12 words: Minimize indoor emissions; keep it dry; ventilate well; protect against outdoor pollution.

What are we breathing?

As a pollutant dynamicist Bill is interested in the composition and complexity of the air we breathe indoors. He concentrates on 3 Ps: 1) Pollutants, 2) People and 3) Places.  “Pollutants” of interest include many specific categories or classes: inorganic vs. organic; volatile vs. semivolatile vs. condensed-phase; and, in the particle phase, biological vs. abiotic.  Regarding “people,” building occupants are the recipients of exposures, their activities contribute to emissions, and even their presence influences the chemical composition of the spaces they occupy.  As for “places,” at a global scale, we are challenged to consider about a billion distinct units.  How can we bring order to this richness?  What categorizations make the most sense?  What should we aim to understand mechanistically and what statistically?

There was recently an EPA conference on exposure assessment can you tell listeners some of the important take away points from that conference?

This past February, a 2-day workshop was held in Washington DC on the “Health Risks of Indoor Exposure to Particulate Matter.”  Here’s a link to the video presentations and to the published summary.  There is also a useful one-page infographic, which can be downloaded here.  (A copy is attached.)  Among the take-away messages:

  • Particles that we breathe indoors come from both outdoor air and from indoor emissions.
  • There are diverse indoor sources, including pets, cooking, candles, cleaning activities, smoking, desktop printers, mold, and chemical reactions (involving components from cleaning products and air fresheners)
  • Particles vary widely in size and we should at least be thinking in three size categories: ultrafine, fine, and coarse.
  • Exposure to high levels of particulate matter do adversely affect health.
  • Major methods for controlling particle exposure are source control, ventilation, and filtration.
  • Particles indoor come from a combination of indoor and outdoor sources.
  • Different of different sizes behave and are controlled differently. Particles from outdoors change indoors. Particles are not inert.

How much do we know about the exposure of building occupants to dampness agents in residential andcommercial buildings?

We know that indicators of dampness and moisture are correlated with increased risk for adverse respiratory effects.  These indicators include visible mold, visible water damage, and moldy odors.  What we don’t know, though, is what causes the health problems.  Microbial exposures are a leading candidate, but proving the case has so far been an unsolvable challenge.  Chemical exposures may contribute, too.  It seems that this is a situation in which exposures are complex, the details may matter, and our technological capability for truly characterizing exposures isn’t yet strong enough to meet the challenge.

Why the interest in the microbiome?

This surge of interest can be traced to the emerging ability to measure aspects of microbiology in much greater detail and much less expensively than before.  We already knew that the indoor environment was important for transmission of certain infectious diseases (tuberculosis, Legionnaires disease, as two examples).  We have also learned that moisture and dampness contribute to respiratory health problems.  Now we are beginning to learn about the many ways in which the human microbiomes are important for our health and wellbeing.  And, we are just beginning to understand the roles that the indoor environment might play contributing to the formation and maintenance of the human microbiome.

Exposure assessment of remediation workers?
The industrial hygiene professional community predates the indoor air research and professional practice community. PPE and appropriate containment are critical concepts to protect both remediation workers and building occupants.

Please opine on ozone and hydroxol generators? 

I haven’t seen enough careful research done to know whether such machines make sense for restorative efforts.  However, I do believe it is a bad idea to use chemical oxidation processes for routine IAQ improvement.  The hydroxyl radical is a key actor in atmospheric photochemical smog.  The nature of atmospheric chemistry initiated by the hydroxyl radical is to convert molecules that are relatively innocuous (alkanes and alkenes for example) into compounds that are health harmful (aldehydes and organic acids, among others).  In nature, OH-initiated chemistry[1] is key to the removal of lots of impurities from the atmosphere, so ultimately that is a good thing.  The problem with applying that process indoors is that the good ultimate outcome can’t be controlled.  The net effect is more likely than not to be bad.

What other pollutant-surface interactions are most important in the study of IAQ

There are at least three categories of interesting and important interactions:

  • Oxidative reactions.  Example: ozone decomposition by reaction on indoor surfaces.  Ozone is destroyed (a good outcome), but the byproducts of the reaction, which can include a range of aldehydes, can be emitted back into the air (a bad outcome).
  • Sorptive interactions.  Example: tobacco smoke odors adhere to indoor surfaces when concentrations are high and then come back off (desorb) when concentrations are low.  The net effect is a persistence of exposure.
  • Deposition and resuspension of particles.  Example: allergens such as mold spores are emitted into indoor air, they settle onto upward facing surfaces (floor, tables), and are later resuspended, e.g. by occupant activities, leading to a renewed exposure opportunity.

What is “exposure science?” Please provide an example of a recent achievement in this areaThe idea in this paper (https://www.ncbi.nlm.nih.gov/pubmed/24328315Dermal uptake of organic vapors commonly found in indoor air.Weschler CJNazaroff WW) represents a paradigm shift for exposure science.  Although the skin is a good barrier generally, we know that some chemicals can pass through the skin fairly readily.  Dermal uptake (transdermal permeation) has long been a recognized part of the exposure world.  Previously, environmental exposure assessments mainly considered that dermal uptake required direct physical contact to initiate the process.  You touch a contaminated surface, pick up some of the contaminant, it penetrates the skin, you are exposed.  The paper cited makes the point that — for many chemicals — the physical contact isn’t necessary.  There is a direct source-to-air-to-human-skin exposure pathway that is meaningful and in fact that can exceed the inhalation pathway.  New experiments at the Technical University of Denmark are proving the case for some phthalates and for nicotine.

Other important points:

  • Mechanical ventilation — Moderate quality filters provide moderate particulate removal; we can (and should) do better.
  • Ammonium nitrate is comprised of nitric acid and ammonia. A moderate fraction of the fine particle mass in California is ammonium nitrate. Ammonium nitrate is temperature reactive changing from a solid to a gas at higher temperature. The outdoor-indoor relationship for ammonium nitrate particles shows greater complexity because of this temperature dependence than for inert constituents, such as ammonium sulfate.
  • Filtration techniques work well on removal of particles not on gasses. There is no inexpensive and broadly effective gas removal method.
  • In Singapore, higher MERV rated filters are proving to provide demonstrable health cost benefits.
  • On IAQ research: People who study indoor pollutants typically have a component that they are focused upon and particularly good at. There is much to be learned from looking elsewhere.
  • Primary gaps in knowledge: Gap 1) what we know and what we practice, and Gap 2) what’s important to know and what we do know. Communication is central to closing the first gap, between research and practice. Researchers need to listen to practitioner’s opinions on what’s important.
  • For every $1 spent on IAQ research, $100 is spent studying atmospheric chemistry. Bill attributes this to no one governmental agency having central responsibility for indoor air quality regulation and maintenance.
  • Four Principles of IAQ: 1) Minimize indoor emissions, 2) keep it dry, 3) ventilate well, 4) protect against outdoor pollution.
  • Sleep environment. Many bedrooms are improperly ventilated. CO2 levels above 1,000 ppm commonly occur while occupants are sleeping. CO2 can impair rest, dreaming and next day performance.
  • Some gas phase molecules are sticky. Those with high molecular weight, chemical cluster, or semi volatile (phthalates, pesticides, and flame retardants) molecules migrate to surfaces and adsorb. These sticky molecules can later desorband cause delayed exposure (i.e. environmental tobacco smoke and the so-called “third-hand” smoke exposure problem).
  • Some particles such as mold spores, pet dander fall out of the air and settle. They can later become resuspended by occupant movement, renewing their potential to cause exposure.
  • Bake-out as a remedial technique.
  • Vaporized hydrogen peroxide has been successfully used in decontamination applications,such as aircraft interiors.

Bill’s closing thought:

The role of personal care products in IAQ. Growing concern over methyl siloxanes used in personal care products.  These chemicals  provide a silky feeling when applied on skin. The materials have low vapor pressure, slowly evaporate and are showing up in more places indoors and outdoors, too. What are the potential consequences?  This example is one of a growing set of issues of interest about specific chemical compound emissions from building occupants.

Today’s Music:

Air Pollution Song  johnnybaustralia   YouTube

Z-Man signing off

Trivia Question:

Name the graduate of the University of California at Berkeley who was elected to the National Academy of Engineering for his “pioneering theoretical, experimental, and design contributions in the development of reentry systems for U.S. Fleet Ballistic Missiles” and who proposed the merger of aerospace firms resulting in the formation of Lockheed Martin.


Daniel Michael Tellep

[1]Hydroxy group – Wikipedia


A hydroxyl or hydroxy group is a chemical functional group containing one oxygen atom connected by a covalent bond to one hydrogen atom (−OH). … When the −OH group participates in an ionic bond, the [OH] anion is called the hydroxide ion. As a free radical, it is the hydroxyl radical.


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