Odor Investigations

 

I do indoor air quality work with schools. Lots of schools are old, and suffer from indoor air quality problems. Odors are a common complaint, but they're a great diagnostic for bad ventilation. Here's a typical situation -- there's a classroom, and across the hall, a bathroom. The bathroom is supposed to have an exhaust fan running all the time, because a bathroom is a potent source of indoor contaminants (and not just from the obvious, but also for the powerful cleaning products used there). If this exhaust fan isn't working,  because maybe the rubber belt connecting the motor to the fan has deteriorated over time, then the air from the bathroom can get sucked into the classroom across the hall. 

This is a problem, obviously. But sometimes it's hard to convince those in charge that it needs fixing. Sometimes nobody knows how to fix it. (Because sometimes, just because you have a job doesn't mean you're good at it.)

When things get real crazy, the workers can convince their employer to get an "air test" in their classroom. This is usually not a good idea, because they will usually not find anything, whether it's there or not, and your problems will thenceforth be dismissed, regardless of their validity. There's other ways of diagnosing indoor air quality problems.

But sometimes it does work. I'm talking about a gas canister sample, sometimes called a TO-15. An environmental specialist will bring a metal canister into your room, twist off the top, and let it suck in the air in your room for a couple minutes. Then they close the canister, bring it back to a lab, release all the air that was sucked in from your room, and analyze it. Then they spit back a long list of the VOC's found, usually scary-sounding chemicals that are actually just your deodorant, hair gel, perfume, etc. But every once in a while, I get a hit on 1,4-Dichlorobenzene, and that's when I can say aha. The air from the bathroom is getting into your classroom. 

The VOC 1,4-Dichlorobenzene is the smell of a urinal cake, also described as "mothball-like." I don't know why it was chosen as THE smell of urinal cakes, but it is, and it doesn't belong in your classroom. 

Had we just fixed the exhaust fan in the first place, we could have skipped all the steps in between. But sometimes things have to be difficult. 

Threat Detection, the Exposome and Olfactory Awareness

Global pandemics are real good for motivating exposure scientists to identify threats in the environment. Add to that the threat detection capabilities of chemosensation (smelling), and you've got some ingredients for a burgeoning field of study that overlaps with olfaction-inspired technologies.

 

Olfaction is for threat detection perhaps above all things, so it is fitting that we see this application become more common. One common use already being implemented by the company Aclima is the distributed air-quality sensor network for pollutants:

 

Early warning sensor sniffs out cities' harmful gas

May 2020, phys.org

 

The IGZO thin-film transistor acts as both an electronic component of the device and also as the NO2-sensing layer. The strongly electron-accepting NO2 molecule is drawn to the electrons on the transistor's surface. The more NO2 molecules that adhere to the IGZO, the more electrons are depleted from its surface, altering its electronic output and triggering an NO2 detection alert.

 

After a detection event, the sensor is reset by reviving the IGZO layer with the light from an integrated blue LED. Similar to a solar cell, the light generates negatively charged electrons and positively charged holes in the IGZO, which neutralizes the adsorbed NO2 and releases it from the surface. "This is the first study to achieve sensing and revival of a semiconducting metal oxide-based thin-film transistor sensor at room temperature," says Surya.

 

*Nitrous oxides (NO2) are a by-product of burning fuel, just like carbon monoxide, carbon dioxide, and sulfur oxides, and all of these are harmful to human health.

 

And here's another related report:

Aerosol-printed graphene unveiled as low cost, faster food toxin sensor

June 2020, phys.org

 

Researchers in the USA have developed a graphene-based electrochemical sensor capable of detecting histamines (allergens) and toxins in food much faster than standard laboratory tests.

 

The team created high-resolution interdigitated electrodes (IDEs) on flexible substrates, which they converted into histamine sensors by covalently linking monoclonal antibodies to oxygen moieties created on the graphene surface by a CO2 thermal annealing process.

 

As an additive manufacturing method that only deposits material where it is needed and therefore minimizes waste, aerosol-jet-printed sensors are low-cost, straightforward to make, and portable. This could potentially enable their use in places where continuous on-site monitoring of food samples is needed to determine and maintain the quality of products, as well as other applications.

 

-Aerosol-jet-printed graphene electrochemical histamine sensors for food safety monitoring, 2-D Materials, DOI: 10.1088/2053-1583/ab8919

 

And still further sensorific developments:

Paper-based device provides low-power, long-term method for analyzing sweat

June 2020, phys.org

 

Using a process known as capillary action, akin to water transport in plants, the device uses evaporation to wick fluid that mimics the features of human sweat to a sensor for up to 10 days or longer.

 

"We expected that the flow of the model sweat will be suppressed by the deposition of a salt layer inside the drying pad," Velev said. "By following the flow of model sweat, we found, quite surprisingly, that such a simple paper construct can achieve continuous sweat pumping and disposal for very long periods."

 

"The biological markers or drug metabolites that seep in the patient's sweat over a long period will be captured on the paper pad and preserved in a time-stamped manner to be analyzed later, similar to tree rings preserving the record of tree development," Dickey said.

 

-Principles of long-term fluids handling in paper-based wearables with capillary-evaporative transport, Biomicrofluidics (2020). aip.scitation.org/doi/10.1063/5.0010417

 

Post Script:

The exposome - When our environment drives health and disease

May 2020, phys.org

 

From this press article: The exposome is the sum of all the environmental drivers of health and diseases: a combination of external factors such as chemicals contained in the air, water or food, and of internal components produced by our organism in response to various stress factors.

 

Notes:

Aclima delivers hyperlocal air pollution and climate emissions intelligence at unprecedented block-by-block resolution.

 

 

 

Clean Air Beware

 

Just when you thought you knew what to do, you don't.

 

Ventilation is good (and a necessary part of controlling an airborne virus, by the way), but opening windows will not remove the chemicals from most homes, at least according to this work done with the HOME Chem model house.

 

Our indoor environments are filled with the chemicals that offgas from just about everything that surrounds us, from body care products to scented candles to building materials. Cleaning products are a major culprit here, and also an important consideration while trying to combat a global pandemic via the war against germs, aka chemical disinfectants, aka indoor environmental chemical warfare.

 

For almost any product you bring into your home, or any activity you perform there, chemicals are released into the air. Not all chemicals are bad, but some of them are. The problem is not even in identifying the "bad" things in the air, but in measuring how much things accumulate, no matter what they are -- everything is bad at the right dose.

 

Opening the windows is the most straightforward and effective way of reducing these concentrations. The problem is that at some point those windows must be closed. Experiments done in the "chem house" show that the concentrations of typical chemicals found indoors do drop precipitously when we open the windows.

 

But surprise -- a few minutes after they're closed, the concentrations go right back up to baseline.

The idea is that the chemicals cling to the walls, likely in the macro- and microscopic nooks and crannies on the surface. They act like reservoirs. Volatile organic compounds will offgas into the room, and especially during cleaning activities for example, where they settle onto those surface microtextures, and then re-volatilize into the air continuously.

 

In conclusion, opening windows is good for flushing chemicals out of the indoor air temporarily, but the real effort must be put into keeping them out in the first place. (Sorry Clorox wipes, I’m looking at you, don't act like you don't offgas.)

 

Image source: The Broom Maker, Victor on Flickr, 2019

 

Post Script:

What produces more voc’s, spraying a perfume on your wrist once a day or cleaning your house with a surface disinfectant once a week? *First of all, cleaning and disinfecting are not the same thing, and second of all, you’re probably over-disinfecting.

 

Notes:

Opening the window in your home will not flush out the chemicals in the air

Feb 2020, phys.org

https://phys.org/news/2020-02-window-home-flush-chemicals-air.html

 

Chen Wang et al. Surface reservoirs dominate dynamic gas-surface partitioning of many indoor air constituents, Science Advances (2020). DOI: 10.1126/sciadv.aay8973

http://dx.doi.org/10.1126/sciadv.aay8973

 

A good follow up:

Organic compounds in indoor air like to accumulate in paint

May 2020, Indoor Chem Blog

https://indoorchem.org/2020/05/paint/

 

Measurements and modeling of absorptive partitioning of volatile organic compounds to painted surfaces. Algrim, L. B., Pagonis, D., de Gouw, J. A.,  Jimenez, J. L.,  and Ziemann P. J. Indoor Air, 2020. 00; 1-12 doi.org/10.1111/ina.12654

https://doi.org/10.1111/ina.12654

 

Further reading:

HOME Chem - House Observations of Microbial and Environmental Chemistry

University of Colorado and CU Boulder

https://indoorchem.org/projects/homechem/

 

ISIAQ - International Society of Indoor Air Quality and Climate

https://iaiq.org