Incentivizing for maximum efficacy and scalability

Our current goal is to design the best possible parameters to incentivize the most scalable solutions in emissions removal technology. We would like to pose a question to the community - based on a very insightful comment from @akb on our last post:

Assuming the technology presents a given area to the polluted air (e.g. as a fan’s intake, or a static surface), it has to extract pollution at a comparable rate to that of the (local) emissions source, or the rate of pollutant delivery (by wind and diffusion). For example, a canyon type street (with no wind) might have to extract pollutants at a similar rate to the total vehicle emissions on that street - but if only part of the street has the clean air technology fitted then it might have to extract pollutants at a faster rate. Admittedly, this complicates matters because we have to know how the technology will be deployed spatially. So rate of extraction might be required, e.g.: micrograms of pollutant per unit surface area (of the technology’s interface) per minute.

We would like you to take your favorite potential solution - filter towers, streetlight fans, electrostatic nets, bioreactors, hybrid solutions etc - and imagine how it might compete in the given competition. How could/should we measure microgram of pollutant removed per unit of surface area?

Hi @hopkepk , @bartc , @djaffe , @Joonas , @dwcollins1960 ,
We are keen to know your thoughts on Terry’s question. Join the discussion.

Thinking about this further, and in the context of the approaches proposed above… Some technologies might be reliant on surface area, whereas others might not. For example, an electrostatic sheet would be surface area related, whereas we might have other different approaches that suck in vast quantities of air at point sinks with little surface area (or several point sinks along a road for example).

So it might be that comparing efficiencies per unit surface area are useful for the former types of approaches (surfaces), but not the latter (points). For point sinks, the rate of extraction per unit of energy consumed (grams per kWh) might be useful (and this could also be applied to surface area technologies too; in addition to the other surface based metric).

Area by itself is not a sufficient parameter. It must go along with velocity. In the example above, a flat surface that is contacted by air (or gas) may be only a low velocity device. That means the total volume of air treated is low. For a point source with a high volume or air (or gas), the volumetric flow rate would still be quite high, even with modest velocity. For an active device (ie not something that is static and waiting for air or gas to come in contact), some kind of fan is typically needed to move the air (or gas). Fans are rated on a volumetric basis (ie cu. ft. per min.). Also, the ambient air standards are rated on mass per unit volume. Therefore, I would suggest that the proper metric would be the mass removed per volume of air or gas treated.

This should work for point sources or ambient air. Even so-called hot spots can use this parameter. The only warning is that the result will not translate directly into an overall reduction in ambient air concentration, unless we treat something like 10% of the total volume of air in the US on an annual basis. If the current ambient air standard of 12 micrograms/Nm3 represented the uniform average concentration across the entire US at all altitudes, the total amount of particulates in the atmosphere would be about 3 million tons. Given that the input to the atmosphere from all sources (natural and man made) is on the order of 500 million tons, the current processes, both natural and man made) are removing some 99.4% of the total inputs. The real question becomes finding the best way to remove the next 1 million tons from the air. It might be to focus on the few remaining non-attainment areas and treat large volumes of that air.

Just a thought, using a line of drones, showering the highly populated ( outdoor ) area with negative ions. Each drone has a negative ions generator and a set of electrostatic charged positive and negative plates. When the drones a sent to the area, Two actions will happen. Billions of negative ions attracting to positively charged dust particles make them so heavy and precipitated to ground. The two charged plates are coated with TIO2. The dirty air pulled in from the drone’s propellers separating air into + and - charge, negatively charged particles attracted to positive plate and vice versa. Because the plates are coated TIO2. The once dirty air exited from the drones will be simply clean CO2 and water. I will put on my website: click Xprice to view. I was working indoor air quality control. This outdoor concept has not been tested. 11-13-19

The useful comments above about surface area, velocity, and volume of air treated make sense, and it got me thinking further about how we would measure these (and other) metrics.

For prototypes that produce an airflow into their technology (e.g. fan based) it would be possible to have an airflow monitor fitted to measure the actual airflow. If this is desired then we should tell the participants in advance that this is one of the requirements (and we would probably want to use standardised/identical monitors).

For mechanically passive surface technologies that have no artificially created airflow, on poor air quality days with no wind (or vertical air currents) the airflow will be low, and in a real-world on-street scenario difficult to measure. Under such conditions pollutants are being dispersed by flowing traffic (turbulent eddy currents) and diffusion. Turbulent air flows, by their nature, do not have a uniform or fixed velocity. This means that real-world airflow velocities will be low and hard to measure on the days when pollution hot spots (e.g. near high traffic flows, junctions, and street canyons) are at their worst - and when the air pollution removal technology is most required (e.g. to keep pollutant concentrations below legal limits).

The above real-world challenges inspired this thought: perhaps we should have two stages in the XPRIZE challenge: laboratory testing followed by real-world testing.

The lab testing allows us to monitor all of the metrics of interest in a controlled environment, which will be the same for all participants. Putting mechanically passive surface technologies in a wind tunnel would allow (an artificial) wind velocity and airflow to be measured, thus allowing measurements to be derived for the quantity of mass extracted per unit volume, if desired. Lab testing has the benefits of providing a well controlled and measured environment, and giving each prototype identical conditions to perform in.

The second phase of real-world testing is clearly of interest to see how prototypes perform in reality under a range of challenging environmental conditions. A one year test across all seasons would also indicate how robust and effective the prototypes are in reality. Looking at the following sketch, we should also put pollution sensors at the head height of pedestrians. [Note that, ironically, young children are often at the most vulnerable height - near the exhaust emissions.]

The micro-grams of pollutant per unit surface area (of the technology’s interface) per minute seems to be a useful metric for those real-world tests on passive surface technologies - for the reasons mentioned above. In the lab it is possible to also use mass extracted per unit volume, as mentioned above.

Another potentially useful metric is mass extracted per unit of energy consumed by the prototype (e.g. grams per kWh). This represents an environmental efficiency type rating. We want to extract a large quantity of pollutants, whilst consuming little energy (because even renewable energy has some environmental impact over its complete lifetime).

It is assumed that air quality monitoring professionals will be used in the lab and real-world trials. They’ll probably want to record additional metrics such as meteorological values (e.g. temperature, pressure, humidity, and wind speed). Note: Prototypes might function at different levels of efficiency as these values change.

Yet another factor to reflect on is the efficiency of a prototype when exposed to different levels (and types) of pollution.

Hi @JosieAtCapture , @ET_Tony , @jwangjun , @Adaryani , @mprakhar ,
Please share your thoughts on how to measure microgram of pollutant removed per unit of surface area. Thanks.

While a passive device would not use much (or any) energy, it’s effectiveness would be poor. Unless air comes in contact with the device, it will not collect any particles. This has been pointed out in several studies relative to indoor particulate concentrations. Filters in HVAC systems only contact air when the fan is running. In most systems, the fan only runs 10 - 15% of the time. Consequently, the indoor particulate concentration doesn’t change very much. If we really want to make a difference, we need to process more air to some kind of cleaning device.

If we do want to evaluate passive devices, then we can estimate the air contact using a diffusion coefficient to estimate the movement of air across the face of the device. This approach may not be entirely accurate, but relative to a fan moving air should be more than adequate. A power plant fan moves 2000 - 3000 tons/hr of air (1 - 1.5 million cubic ft/min). A passive device would be orders of magnitude less. Even a factor of 10 in the estimate for a static device would not make much difference when compared to an active device.

I share your concerns @carlbozzuto about the effectiveness of a passive device. Even an active device (outdoors) might have to face a huge challenge, as you hint at with the numbers.

Hello @swihera , @Ananya_Roy , @Cerruti , @rohan9602 , @yusef , @avidela ,
@DanBowden , @hannusalmela , @Chandra_Bhushan , @alanDRI , @mccubbin , @rgschreib ,
We would love to hear your thoughts. Join the discussion. Thanks,

Any thoughts on how to measure pollution extraction @sagnikdey, @themben , @mlacey , @bontempi , @mskoehle , @hlee